Recent papers

Recent papers
(department members in bold)

 Jezbera J, Jezberová J, Kasalický V, Šimek K, Hahn MW. 2013: Patterns of Limnohabitans Microdiversity across a Large Set of Freshwater Habitats as Revealed by Reverse Line Blot Hybridization. PLoS ONE 8(3): e58527. doi:10.1371/journal.pone.0058527

Among abundant freshwater Betaproteobacteria, only few groups are considered to be of central ecological importance. One of them is the well-studied genus Limnohabitans and mainly its R-BT subcluster, investigated previously mainly by fluorescence in situ hybridization methods. We designed, based on sequences from a large Limnohabitans culture collection, 18 RLBH (Reverse Line Blot Hybridization) probes specific for different groups within the genus Limnohabitans by targeting diagnostic sequences on their 16 S-23 S rRNA ITS regions. The developed probes covered in sum 92% of the available isolates. This set of probes was applied to environmental DNA originating from 161 different European standing freshwater habitats to reveal the microdiversity (intra-genus) patterns of the Limnohabitans genus along a pH gradient. Investigated habitats differed in various physicochemical parameters, and represented a very broad range of standing freshwater habitats. The Limnohabitans microdiversity, assessed as number of RLBH-defined groups detected, increased significantly along the gradient of rising pH of habitats. 14 out of 18 probes returned detection signals that allowed predictions on the distribution of distinct Limnohabitans groups. Most probe-defined Limnohabitans groups showed preferences for alkaline habitats, one for acidic, and some seemed to lack preferences. Complete niche-separation was indicated for some of the probe-targeted groups. Moreover, bimodal distributions observed for some groups of Limnohabitans, suggested further niche separation between genotypes within the same probe-defined group. Statistical analyses suggested that different environmental parameters such as pH, conductivity, oxygen and altitude influenced the distribution of distinct groups. The results of our study do not support the hypothesis that the wide ecological distribution of Limnohabitans bacteria in standing freshwater habitats results from generalist adaptations of these bacteria. Instead, our observations suggest that the genus Limnohabitans, as well as its R-BT subgroup, represent ecologically heterogeneous taxa, which underwent pronounced ecological diversification.

Jezberová J, Jezbera J, Hahn MW. 2013: Insights into Variability of Actinorhodopsin Genes of the LG1 Cluster in Two Different Freshwater Habitats. PLoS ONE 8(7): e68542. doi:10.1371/journal.pone.0068542

Actinorhodopsins (ActRs) are recently discovered proteorhodopsins present in Actinobacteria, enabling them to adapt to a wider spectrum of environmental conditions. Frequently, a large fraction of freshwater bacterioplankton belongs to the acI lineage of Actinobacteria and codes the LG1 type of ActRs. In this paper we studied the genotype variability of the LG1 ActRs. We have constructed two clone libraries originating from two environmentally different habitats located in Central Europe; the large alkaline lake Mondsee (Austria) and the small humic reservoir Jiřická (the Czech Republic). The 75 yielded clones were phylogenetically analyzed together with all ActR sequences currently available in public databases. Altogether 156 sequences were analyzed and 13 clusters of ActRs were distinguished. Newly obtained clones are distributed over all three LG1 subgroups - LG1-A, B and C. Eighty percent of the sequences belonged to the acI lineage (LG1-A ActR gene bearers) further divided into LG1-A1 and LG1-A2 subgroups. Interestingly, the two habitats markedly differed in genotype composition with no identical sequence found in both samples of clones. Moreover, Jiřická reservoir contained three so far not reported clusters, one of them LG1-C related, presenting thus completely new, so far undescribed, genotypes of Actinobacteria in freshwaters.

Šimek K, Kasalický V, Jezbera J, Horňák K, Nedoma J, Hahn MW, Bass D, Jost S, Boenigk J. 2013: Differential freshwater flagellate community response to bacterial food quality with a focus on Limnohabitans bacteria. ISME J. 7(8): 1519-1530. (Featured Article)

Different bacterial strains can have different value as food for heterotrophic nanoflagellates (HNF), thus modulating HNF growth and community composition. We examined the influence of prey food quality using four Limnohabitans strains, one Polynucleobacter strain and one freshwater actinobacterial strain on growth (growth rate, length of lag phase and growth efficiency) and community composition of a natural HNF community from a freshwater reservoir. Pyrosequencing of eukaryotic small subunit rRNA amplicons was used to assess time-course changes in HNF community composition. All four Limnohabitans strains and the Polynucleobacter strain yielded significant HNF community growth while the actinobacterial strain did not although it was detected in HNF food vacuoles. Notably, even within the Limnohabitans strains we found significant prey-related differences in HNF growth parameters, which could not be related only to size of the bacterial prey. Sequence data characterizing the HNF communities showed also that different bacterial prey items induced highly significant differences in community composition of flagellates. Generally, Stramenopiles dominated the communities and phylotypes closely related to Pedospumella (Chrysophyceae) were most abundant bacterivorous flagellates rapidly reacting to addition of the bacterial prey of high food quality.

Kasalický V, Jezbera J, Hahn MW, Šimek K. 2013: The Diversity of the Limnohabitans Genus, an Important Group of Freshwater Bacterioplankton, by Characterization of 35 Isolated Strains. PLoS ONE 8(3): e58209. doi:10.1371/journal.pone.0058209

Bacteria of the genus Limnohabitans, more precisely the R-BT lineage, have a prominent role in freshwater bacterioplankton communities due to their high rates of substrate uptake and growth, growth on algal-derived substrates and high mortality rates from bacterivory. Moreover, due to their generally larger mean cell volume, compared to typical bacterioplankton cells, they contribute over-proportionally to total bacterioplankton biomass. Here we present genetic, morphological and ecophysiological properties of 35 bacterial strains affiliated with the Limnohabitans genus newly isolated from 11 non-acidic European freshwater habitats. The low genetic diversity indicated by the previous studies using the ribosomal SSU gene highly contrasted with the surprisingly rich morphologies and different patterns in substrate utilization of isolated strains. Therefore, the intergenic spacer between 16S and 23S rRNA genes was successfully tested as a fine-scale marker to delineate individual lineages and even genotypes. For further studies, we propose the division of the Limnohabitans genus into five lineages (provisionally named as LimA, LimB, LimC, LimD and LimE) and also additional sublineages within the most diversified lineage LimC. Such a delineation is supported by the morphology of isolated strains which predetermine large differences in their ecology.

Zeng, Y, Kasalický V, Šimek K, & Koblížek M. 2012: Genome sequences of two freshwater Betaproteobacterial isolates, Limnohabitans species strains Rim28 and Rim47, indicate their capabilities as both photoautotrophs and ammonia oxidizers. J Bacteriol 194: 6302-6303.

Betaproteobacterial genus Limnohabitans represents an important part of freshwater bacterioplankton. Here, we report genome sequences of two Limnohabitans isolates, Rim28 and Rim47. They contain a complete photosynthesis gene cluster, RuBisCO, CO dehydrogenase, ammonia monooxygenase, and sulfur-oxidizing genes, which indicates a great metabolic versatility of the Limnohabitans species.

Horňák K, Corno G. 2012: Every Coin Has a Back Side: Invasion by Limnohabitans planktonicusPromotes the Maintenance of Species Diversity in Bacterial Communities. PLoS ONE 7(12): e51576. doi:10.1371/journal.pone.0051576

One of the earliest challenges for ecologists has been to study the impact of invasive species on microbial communities. Although bacteria are fundamental in biological processes, current knowledge on invasion effects by aquatic non-pathogenic bacteria is still limited. Using pure cultures of diverse planktonic bacteria as model organisms at two different carbon concentration levels, we tested the response of an assembled community to the invasion by Limnohabitans planktonicus, an opportunistic bacterium, successful in freshwaters. The invader, introduced at the early stationary growth phase of the resident community, caused a strong decrement of the abundance of the dominant species. This was due to competition for nutrients and a potential allelopathic interaction. Simultaneously, resident species formerly unable to successfully compete within the community, thus potentially exposed to competitive exclusion, increased their abundances. The overall result of the invasion was preservation of species diversity, the higher the lower was the substrate content available. Our study provides new insights into bacterial invasions, offering an alternative interpretation of invasions for community ecology.

Znachor P, Šimek K & Nedoma J. 2012: Bacterial colonization of the freshwater planktonic diatom Fragilaria crotonensis. Aquat Microb Ecol 66: 87-94.

In 2006, the seasonal course of bacterial colonization and silification rates of a colonial diatom Fragilaria crotonensis were studied at 2 distinct depths (surface, 0.5 m and Zeu, the depth of 1% remaining surface photosynthetically active radiation) in the eutrophic Římov Reservoir (Czech Republic). In the study period (July to September), Fragilaria dominated the phytoplankton and formed remarkable subsurface peaks of biomass at Zeu. Diatoms living under light-limited conditions at Zeu displayed lower silification rates measured with the fluorescence probe 2-(4-pyridyl)-5-{[4-(2-dimethylaminoethyl-aminocarbamoyl)methoxy]phenyl} oxazole (PDMPO) and were significantly more colonized by bacteria than at the surface (seasonal means 7.8 and 5.0 bacteria per Fragilaria cell, respectively). In 3 additional experiments using double-stained Fragilaria cells (PDMPO and 4,6-diamidino-2-phenylindole [DAPI]), diatom cells with no PDMPO fluorescence were significantly more colonized by bacteria regardless of the depth, indicating that bacterial colonization reflects the physiological state of the diatoms. As an apparent consequence of a flood event in August, the Fragilaria assemblage was composed of 2 temporally isolated sub-populations differing markedly in the cell length, cell surface area and extent of bacterial colonization. Although both Fragilaria sub-populations showed similar silification rates, the late summer (post-flood) Fragilaria sub-population with smaller cells showed a significantly lower bacterial colonization, while the difference in bacterial colonization between the depths remained consistently significant throughout the study. Our results imply that bacterial colonization of diatom cell surfaces is modulated by both diatom growth and changes in population structure over the season.

Čtvrtlíková M., Znachor P., Nedoma J. & Vrba J. 2012: Effects of temperature on the phenology of germination of Isoëtes echinospora. Preslia 84: 141-153.

Isoëtes echinospora, a submerged aquatic quillwort, is native in northern latitudes and a rare glacial relict in mountain lakes of temperate Central Europe. A relic population of the quillwort in Plešné Lake has recovered recently from a thirty-year period of reproduction failure caused by acidification. Early ontogenetic stages of the quillwort have been considered most vulnerable to environmental changes. Therefore, the objective of this study was to investigate germination phenology of I. echinospora. In two-year experiments, we examined a time course of micro- and macrospore germination and sporeling establishment under (i) natural in situ conditions in Plešné Lake and (ii) various temperatures (6-17°C) in the laboratory. We developed a mathematical model allowing for evaluation of temperature-specific temporal changes in the early ontogeny of I. echinospora. Our experiments clearly showed that spores did not germinate at once but gradually over time if they were exposed to favourable temperatures. Generally, spore germination tended to increase over the season under most temperature regimes while germination was hindered at the lowest temperature. With increasing temperature, microspores germinated earlier and more successfully than macrospores, as described by the model. Sporeling development was also enhanced by higher temperature. However, the highest temperature used in the experiments (17°C) resulted in a marked disorder of the germination phenology of I. echinospora making the spores unavailable for fertilization at the same time. Interactions between temperatures and quillwort reproduction phenology might threaten this species in ongoing climate change.

Kohout P., Sýkorová Z., Čtvrtlíková M., Rydlová J., Suda J., Vohník M. & Sudová R. 2012: Surprising spectra of root-associated fungi in submerged aquatic plants. FEMS Microbiology Ecology 80: 216-235.

Similarly to plants from terrestrial ecosystems, aquatic species harbour wide spectra of root-associated fungi (RAF). However, comparably less is known about fungal diversity in submerged roots. We assessed the incidence and diversity of RAF in submerged aquatic plants using microscopy, culture-dependent and culture-independent techniques. We studied RAF of five submerged isoetid species collected in four oligotrophic freshwater lakes in Norway. Levels of dark septate endophytes (DSE) colonization differed among the lakes and were positively related to the organic matter content and negatively related to pH. In total, we identified 41 fungal OTUs using culture-dependent and culture-independent techniques, belonging to Mucoromycotina, Chytridiomycota, Glomeromycota, Ascomycota as well as Basidiomycota. Sequences corresponding to aquatic hyphomycetes (e.g. Nectria lugdunensis, Tetracladium furcatum and Varicosporium elodeae) were obtained. Eight arbuscular mycorrhizal taxa belonging to the orders Archaeosporales, Diversisporales and Glomerales were also detected. However, the vast majority of the fungal species detected (e.g. Ceratobasidium sp., Cryptosporiopsis rhizophila, Leptodontidium orchidicola, and Tuber sp.) have previously been known only from roots of terrestrial plants. The abundance and phylogenetic distribution of mycorrhizal as well as nonmycorrhizal fungi in the roots of submerged plants have reshaped our views on the fungal diversity in aquatic environment.

Horňák K, Zeder M, Blom JF, Posch T, Pernthaler J. 2012: Suboptimal light conditions negatively affect the heterotrophy of Planktothrix rubescens but are beneficial for accompanying Limnohabitans spp. Environ Microbiol 14: 765-778

We examined the effect of light on the heterotrophic activity of the filamentous cyanobacterium Planktothrix rubescens and on its relationship with the accompanying bacteria. In situ leucine uptake by bacteria and cyanobacteria was determined in a subalpine mesotrophic lake, and natural assemblages from the zone of maximal P. rubescens abundances were incubated for 2 days at contrasting light regimes (ambient, 100× increased, dark). Planktothrix rubescens from the photic zone of the lake incorporated substantially more leucine, but some heterotrophic activity was maintained in filaments from the hypolimnion. Exposure of cyanobacteria to increased irradiance or darkness resulted in significantly lower leucine incorporation than at ambient light conditions. Highest abundances and leucine uptake of Betaproteobacteria from the genus Limnohabitans were found in the accompanying microflora at suboptimal irradiance levels for P. rubescens or in dark incubations. Therefore, two Limnohabitans strains (representing different species) were co-cultured with axenic P. rubescens at different light conditions. The abundances and leucine incorporation rates of both strains most strongly increased at elevated irradiance levels, in parallel to a decrease of photosynthetic pigment fluorescence and the fragmentation of cyanobacterial filaments. Our results suggest that Limnohabitans spp. in lakes might profit from the presence of physiologically stressed P. rubescens.

Jezbera J, Jezberová J, Koll U, Hornák K, Šimek K, Hahn MW. 2012: Contrasting trends in distribution of four major planktonic betaproteobacterial groups along a pH gradient of epilimnia of 72 freshwater habitats. FEMS Microb Ecol: DOI: 10.1111/j.1574-6941.2012.01372.x

The distribution and abundance of Betaproteobacteria and three of its genera - Limnohabitans (R-BT065 lineage), Polynucleobacter (including subclusters Polynucleobacter necessarius and Polynucleobacter acidiphobus/Polynucleobacter difficilis), and Methylophilus - across the epilimnia of 72 limnologically diverse freshwater habitats were investigated using fluorescence in situ hybridization. Moreover, seasonal development of Betaproteobacteria subgroups along the longitudinal axis of a reservoir was followed. Betaproteobacteria comprised on average 29.1%, Polynucleobacter 11.6%, P. necessarius 10.1%, P. acidiphobus/ difficilis 0.5%, Limnohabitans 8.9%, and Methylophilus 0.9% of total bacterioplankton cells in the investigated habitats. Polynucleobacter necessarius and Limnohabitans coexisted in the majority of habitats but showed contrasting abundance patterns along the pH gradient of habitats (pH, 3.8-8.5). The observed distribution patterns could theoretically be explained by different preferences for substrate sources, that is, substances of humic origin in acidic waters and algal-derived substances in alkaline waters. However, substrate utilization patterns observed in laboratory experiments indicate no coherent groupspecific differences in substrate preferences. Interestingly, similar distribution patterns were revealed for Limnohabitans and P. acidiphobus/difficilis, suggesting similar ecological adaptations of these distantly related taxa. Our findings further emphasize that at least two taxa of freshwater Betaproteobacteria represent ecologically diversified groups. Investigations at higher phylogenetic resolution are required for obtaining further insights into their ecology.

Hahn MW, Scheuerl T, Jezberová J, Koll U, Jezbera J, Šimek K, Vannini C, Petroni G, Wu QL. 2012: The Passive Yet Successful Way of Planktonic Life: Genomic and Experimental Analysis of the Ecology of a Free-Living Polynucleobacter Population. PLoS ONE 7(3): e32772. doi:10.1371/journal.pone.0032772


The bacterial taxon Polynucleobacter necessarius subspecies asymbioticus represents a group of planktonic freshwater bacteria with cosmopolitan and ubiquitous distribution in standing freshwater habitats. These bacteria comprise ,1% to 70% (on average about 20%) of total bacterioplankton cells in various freshwater habitats. The ubiquity of this taxon was recently explained by intra-taxon ecological diversification, i.e. specialization of lineages to specific environmental conditions; however, details on specific adaptations are not known. Here we investigated by means of genomic and experimental analyses the ecological adaptation of a persistent population dwelling in a small acidic pond. The investigated population (F10 lineage) contributed on average 11% to total bacterioplankton in the pond during the vegetation periods (ice-free period, usually May to November). Only a low degree of genetic diversification of the population could be revealed. These bacteria are characterized by a small genome size (2.1 Mb), a relatively small number of genes involved in transduction of environmental signals, and the lack of motility and quorum sensing. Experiments indicated that these bacteria live as chemoorganotrophs by mainly utilizing low-molecular-weight substrates derived from photooxidation of humic substances. Evolutionary genome streamlining resulted in a highly passive lifestyle so far only known among free-living bacteria from pelagic marine taxa dwelling in environmentally stable nutrient-poor off-shore systems. Surprisingly, such a lifestyle is also successful in a highly dynamic and nutrient-richer environment such as the water column of the investigated pond, which was undergoing complete mixis and pronounced stratification in diurnal cycles. Obviously, metabolic and ecological versatility is not a prerequisite for long-lasting establishment of abundant bacterial populations under highly dynamic environmental conditions. Caution should be exercised when generalizing the obtained insights into the ecology and adaptation of the investigated lineage to other Polynucleobacter lineages.

Šimek K, Kasalický V, Zapomělová E, Horňák K. 2011: Alga-derived substrates select for distinct betaproteobacterial lineages and contribute to niche separation in Limnohabitans strains. Appl Environ Microbiol 77: 7307-7315.

We examined the proportions of major Betaproteobacteria subgroups within bacterial communities in diverse nonaxenic, monospecific cultures of algae or cyanobacteria: four species of cryptophyta (genera Cryptomonas and Rhodomonas), four species of chlorophyta (genera Pediastrum, Staurastrum, and Chlamydomonas), and two species of cyanobacteria (genera Dolichospermum and Aphanizomenon). In the cryptophyta cultures, Betaproteobacteria represented 48 to 71% of total bacteria, the genus Limnohabitans represented 18 to 26%, and the Polynucleobacter B subcluster represented 5 to 16%. In the taxonomically diverse chlorophyta group, the genus Limnohabitans accounted for 7 to 45% of total bacteria. In contrast, cyanobacterial cultures contained significantly lower proportions of the Limnohabitans bacteria (1 to 3% of the total) than the cryptophyta and chlorophyta cultures. Notably, largely absent in all of the cultures was Polynucleobacter necessarius (Polynucleobacter C subcluster). Subsequently, we examined the growth of Limnohabitans strains in the presence of different algae or their extracellular products (EPP). Two strains, affiliated with Limnohabitans planktonicus and Limnohabitans parvus, were separately inoculated into axenic cultures of three algal species growing in an inorganic medium: Cryptomonas sp., Chlamydomonas noctigama, and Pediastrum boryanum. The Limnohabitans strains cocultured with these algae or inoculated into their EPP consistently showed (i) pronounced population growth compared to the control without the algae or EPP and (ii) stronger growth stimulation of L. planktonicus than of L. parvus. Overall, growth responses of the Limnohabitans strains cultured with algae were highly species specific, which suggests a pronounced niche separation between two closely related Limnohabitans species likely mediated by different abilities to utilize the substrates produced by different algal species.

Sudová R, Rydlová J, Čtvrtlíková M, Havránek P, Adamec L. 2011: The incidence of arbuscular mycorrhiza in two submerged Isoëtes species. Aquatic Botany 94: 183-187.

We investigated the occurrence of arbuscular mycorrhizal fungi in the roots of Isoëtes lacustris and I. echinospora. These submerged lycopsids are the only macrophyte species inhabiting the bottom of two acidified glacial lakes in the Czech Republic. Arbuscular mycorrhizal (AM) fungi were detected in the roots of both species but the percentage of root colonization was both low and variable. Nevertheless, planting Littorella uniflora in the sediments from Isoëtes rhizosphere revealed high levels of viable AM propagules in both lakes. While AM colonization of Isoëtes roots did not exceed 25%, the average colonization of Littorella roots amounted to more than 80%. Although colonization of quillwort roots by AM fungi is evident, the taxonomic identity and role of these AM fungi in plant growth remain unclear. In addition to AM fungi, root-colonizing dark septate endophytic fungi were observed in both Isoëtes species.

Znachor P, Nedoma J, Rychtecký P. 2011: Kinetics of glucose stimulatory effect on silica deposition and growth of natural populations of Fragilaria crotonensis. Phycological Research 59: 123-128.

Diatoms are known to exploit organic substrates for growth; however, convincing evidence that they can utilize dissolved organic carbon under natural conditions is not available. In 2008-2009, we performed in situ experiments examining the effect of glucose addition on silica deposition kinetics and growth rates of Fragilaria crotonensis in the eutrophic Rimov Reservoir (Czech Republic). Silica deposition kinetics was measured at 4-h intervals over a 24-h incubation with PDMPO [2-(4-pyridyl)-5{[4-dimethylaminoethyl-aminocarbamyl)-methoxy] phenyl}oxazole] fluorescence probe. A significant stimulatory effect of glucose supplemented at the concentration of 10-4 M on Fragilaria silification was observed at 20 and 24 h. Fragilaria growth rates almost doubled upon glucose enrichment compared with the untreated control at 24 h. In addition, we conducted a dose-response experiment testing the glucose additions from 10-8 to 10-3 M in a 24-h incubation. Glucose stimulated both Fragilaria silification and growth at concentrations > 10-7 M, which might occasionally occur in a reservoir as a result of accidental contamination of water by organic pollution.

Rychtecký P, Znachor P. 2011: Spatial heterogeneity and seasonal succession of phytoplankton along the longitudinal gradient in a eutrophic reservoir. Hydrobiologia 663: 175–186.

In order to evaluate the effects of contrasting hydrological scenarios on the spatial and temporal heterogeneity of phytoplankton in a reservoir, vertical chlorophyll and temperature profiles were measured and functional classification of phytoplankton was applied. From April to October 2007, at 1-2 week intervals, seasonal changes in various parameters were studied along the longitudinal axis of the canyon-shaped, eutrophic A similar to imov Reservoir (Czech Republic). At the river inflow, phytoplankton markedly differed from the rest of the reservoir, being dominated by functional groups D and J (pennate diatoms and chlorococcal algae) without a clear seasonal pattern. From April to mid-June, groups Y and P (large cryptophytes and colonial diatoms) prevailed in the whole reservoir. Phytoplankton spatial heterogeneity was the most apparent during the summer reflecting a pronounced gradient of environmental parameters from the river inflow to the dam (e.g., decreasing nutrients, increasing light availability, etc.). A dense cyanobacterial bloom (groups H1 and M) developed in the nutrient-rich transition zone, while functional Group N (desmids) dominated the phytoplankton at the same time at the dam area. In late summer, a sudden flood event considerably disrupted thermal stratification, altered nutrient and light availability, and later even resulted in cyanobacterial dominance in the whole reservoir. Additionally, our study emphasizes the importance of having an intensive phytoplankton monitoring program, which would allow for detecting severe consequences of sudden flood events on phytoplankton spatial and temporal heterogeneity, which significantly affect water quality at the dam area used for drinking water purposes.

Sirová D, Borovec J, Picek T, Adamec L, Nedbalová L, Vrba J. 2011: Ecological implications of organic carbon dynamics in the traps of aquatic carnivorous Utricularia plants. Functional Plant Biology 38: 583-593.

Rootless aquatic carnivorous Utricularia exude up to 25% of their photosynthates into the trap lumen, which also harbours a complex microbial community thought to play a role in enhancing Utricularia nutrient acquisition. We investigated the composition of organic carbon in the trap fluid, its availability for microbial uptake, the influence of plant nutrient status and trap age on its biodegradability, and the composition of prokaryotic assemblages within the traps of three aquatic Utricularia species. Using ion chromatography and basal respiration rate measurements we confirmed that up to 30% of total dissolved organic carbon in Utricularia trap fluid in oligotrophic conditions was easily biodegradable compounds commonly found in plant root exudates (mainly glucose, fructose and lactate). The proportion of these compounds and their microbial utilisation decreased with increasing mineral nutrient supply and trap age. Fluorescence in situ hybridisation analyses showed that microbial trap assemblages are dominated by alpha and beta Proteobacteria, and that the assemblage composition is affected by changes in the ambient mineral nutrient supply. We suggest that organic carbon dynamics within the traps, involving both the plant and associated microbial assemblages, underlies the acquisition of key nutrients by Utricularia and may help explain the evolutionary success of the genus.

Skácelová O, Zapomělová E. 2010: Remarks on the occurrence and ecology of several interesting cyanobacterial morphospecies found in South Moravian wetlands. Acta Musei Moraviae, Scientiae biologicae (Brno) 95: 201-221.

Extensive investigation of planktonic, periphytic, metaphytic and benthic cyanobacteria was performed in the years 1986-2009 at South Moravian localities. The occurrence and ekology of eight selected cyanobacterial morphospecies were studied in detail: Rhabdogloea smithii (R. et E. Chodat) Komárek, Merismopedia convoluta Brébisson in Kützing, 1849, Merismopedia sp., Spirulina major Kützing ex Gomont, 1892, Spirulina meneghiniana Zanardini ex Gomont, 1892, Spirulina nordstedtii Gomont, 1892, Arthrospira jenneri Stizenberger ex Gomont, 1892, non-planktonic morphospecies of Anabaena Bory ex Bornet et Flahault, 1888, and Anabaenopsis nadsonii Woronichin, 1929. This research revealed Anabaenopsis nadsonii as a species new for the Czech Republic. Further, the environmental preferences of the species studied are here revised and discussed together with data in the literature. Spirulina meneghiniana (Kutnar, Pastvisko - Nová okrouhlá tůň Pool, Lednické rybníky fishponds - Prostřední rybník Pond) have been found to display a markedly wider range of conductivity tolerances than had been previously reported. All samples collected in the course of the work have been deposited in the collection of Moravian Museum, Brno and are available for further studies.

Zapomělová E, Hrouzek P, Řezanka T, Jezberová J, Řeháková K, Hisem D, Komárková J. 2011: Polyphasic characterization of Dolichospermum spp. and Sphaerospermopsis spp. (Nostocales, Cyanobacteria) in terms of morphologies, 16S rRNA gene sequences, fatty acid profiles and secondary metabolites. J Phycol in press: DOI: 10.1111/j.1529-8817.2011.01034.x

The genera Dolichospermum (Ralfs ex Bornet et Flahault) Wacklin et al. and Sphaerospermopsis Zapomělová et al. represent a highly diversified group of planktonic cyanobacteria that have been recently separated from the traditional genus Anabaena Bory ex Bornet et Flahault. In this study, morphological diversity, phylogeny of 16S rRNA gene, production of fatty acids and secondary metabolite profiles were evaluated in 33 strains of 14 morphospecies isolated from the Czech Republic. Clustering of the strains based on 16S rRNA gene sequences corresponded to wider groups of species in terms of morphology. On the contrary, the overall secondary metabolite and fatty acid profiles were neither correlated to each other, nor to the 16S rRNA phylogeny and morphology of the strains. Nevertheless, a minor part of the detected secondary metabolites (19% of all compounds) were present solely in the closest relatives and can be thus considered as autapomorphic features.

Hisem D, Hrouzek P, Tomek P, Tomšíčková J, Zapomělová E, Skácelová K, Lukešová A, Kopecký J. 2011: Cyanobacterial cytotoxicity versus toxicity to brine shrimp Artemia salina. Toxicon 57: 76-83.

Heterocytous cyanobacteria from various habitats were screened for toxicity to brine shrimp Artemia salina and the murine lymphoblastic cell line Sp/2 in order to compare these two testing models for evaluation of risk posed by cyanobacteria to human health. Methanol extracts of biomass and cultivation media were tested for toxicity and selected extracts were fractionated to determine the active fraction. We found a significant toxic effect to A. salina and to Sp/2 cells in 5.2% and 31% of studied extracts, respectively. Only 8.6% of the tested strains were highly toxic to both A. salina and the Sp/2 cell line, and only two of the tested strains were toxic to A. salina and not to the murine cell line. Therefore, it is likely that the toxic effect of cyanobacterial secondary metabolites mostly targets basal metabolic pathways present in mammal cells and so is not manifested in A. salina. We conclude that it is insufficient to monitor cytotoxicity of cyanobacteria using only the brine shrimp bioassay as was usual in the past, since cytotoxicity is a more frequent feature in cyanobacteria in comparison with toxicity to A. salina. A. salina toxicity test should not be used when estimating the possible health risk for humans. We suggest that in vitro mammal cells be used for these purposes.

Řeháková K, Chlumská Z, Doležal J. 2011: Soil Cyanobacterial and microalgal diversity in dry mountains of Ladakh, NW Himalaya, as related to site, altitude, and vegetation. Microb Ecol 62:337-346. DOI 10.1007/s00248-011-9878-8

Although phototrophic microbial communities are important components of soils in arid and semi-arid ecosystems around the world, the knowledge of their taxonomic composition and dependency on soil chemistry and vegetation is still fragmentary. We studied the abundance and the diversity of cyanobacteria and eukaryotic microalgae along altitudinal gradients (3,700-5,970 m) at four sites in the dry mountains of Ladakh (Little Tibet, Zanskar Mountains, and Eastern Karakoram), using epifluorescence. The effects of environmental factors (altitude, mountain range, and vegetation type) on soil physicochemical parameters (pH; texture; organic matter, nitrogen, ammonia, and phosphorus contents; and concentration of chlorophylls and carotenoids) and on the composition and biovolume of phototrophs were tested by multivariate redundancy analysis and variance partitioning. Phototrophs were identified in all collected samples, and phototroph biovolume ranged from 0.08 to 0.32 mm3 g-1 dry weight. The dominant component was cyanobacteria, which represented 70.9% to 98.6% of the biovolume. Cyanobacterial species richness was low in that only 28 morphotypes were detected. The biovolume of Oscillatoriales consisted mainly of Phormidium spp. and Microcoleus vaginatus. The environmental factors accounted for 43.8% of the total variability in microbial and soil data, 20.6% of which was explained solely by mountain range, 7.0% by altitude, and 8.4% by vegetation type. Oscillatoriales prevailed in alpine meadows (which had relatively high organic matter and fine soil texture), while Nostocales dominated in the subnival zone and screes. Eukaryotic microalgae together with cyanobacteria in the order Chroococcales were mostly present in the subnival zone. We conclude that the high elevation, semiarid, and arid soils in Ladakh are suitable habitats for microbial phototrophic communities and that the differences in these communities are associated with site, altitude, and vegetation type.

Johansen JR, Řeháková K, Acker F. 2011: Tapinothrix ozarkiana sp. nov., with notes on distribution for the genus in North America. - Fottea 11 (1): 141-148.

A total of 77 samples from streams and rivers were found to contain populations of Tapinothrix (Pseudanabaenaceae), a genus currently confused with Homoeothrix (Oscillatoriaceae). Three species within the genus were identified: T. ozarkiana sp. nov., T. varians. and T. janthina.

Kopylov AI, Kosolapov DB, Zabotkina EA, Straškrábová V. 2010: Distribution of picocyanobacteria and virioplankton in mesotrophic and eutrophic reservoirs: the role of viruses in mortality of picocyanobacteria. Biology Bulletin 37: 565-573

The quantitative distribution and relationships of picocyanobacteria and viruses were studied in the mesotrophic Sheksna and mesoeutrophic Rybinsk reservoirs belonging to the system of the Volga-Baltic Waterway. The share of picocyanobacteria in the sum biomass and production of phytoplankton decreased along with increase in the productivity in the waterbody. However, the abundance of virioplankton increased in such conditions. The extent of infection by phages and virus-induced mortality of picocyanobacteria were two times higher on average in the mesoeutrophic reservoir compared to the mesotrophic one: 14 and 7% of the number of picocyanobacteria, 21 and 11% of daily production of picocyanobacteria, respectively. Mortality in picocyanobacteria resulted from lysis by viruses increased (up to 52% of daily production of picocyanobacteria) at the local parts where water was blooming with phytoplankton and at the parts affected by communal pollution.
DOI:10.1134/S1062359010060038

Jezbera J, Jezberová J, Brandt U, Hahn MW. 2011: Ubiquity of Polynucleobacter necessarius subspecies asymbioticus results from ecological diversification. Environ Microbiol 4: 922-931.

The subspecies Polynucleobacter necessarius asymbioticus (> 99% 16S rRNA similarity) has a cosmopolitan distribution and a ubiquitous occurrence in lentic freshwater habitats. We tested if the observed ubiquity of these free-living planktonic freshwater bacteria results from a euryoecious (generalist) adaptation of P. n. asymbioticusstrains, or from ecological diversification within the subspecies. We developed a reverse line blot hybridization assay enabling the cultivation-independent detection of 13 groups within the subspecies in environmental samples. A set of 121 lentic freshwater habitats, spanning a broad variety of habitat types (e.g. pH levels ranging from 3.8 to 8.5) was investigated for the presence of these 13 P. n. asymbioticus groups. Statistical analyses of the reverse line blot hybridization detections revealed pronounced differences in habitat preferences of several of the groups. Their preferences differed regarding pH, conductivity, dissolved organic carbon and oxygen concentration of habitats. For some groups, differences in environmental preferences resulted even in complete niche separation between them. The revealed differences in habitat preferences suggest that the previously reported ubiquity of P. n. asymbioticus results from ecological diversification within the taxon and not from generalist adaptation of strains.

Weinbauer MG, Bonilla-Findji O, Chan AM, Dolan J, Short SM, Šimek K, Wilhelm SW, Suttle CA. 2011: Synechococcus growth in the ocean may depend on the lysis of heterotrophic bacteria. J Plankton Res 33: 1465-1476.

In experiments designed primarily to investigate viral lysis, we found that the presence of viruses had a positive effect on the growth of Synechococcus. A Landry-Hassett-type stepwise dilution experiment conducted during a Synechococcus bloom in the Gulf of Mexico used both (i) 0.2-mm filtered seawater in which the abundance of bacteria and grazers were reduced but the majority of viruses were retained, and (ii) ultrafiltered (30 000 MW cutoff ) virus-free seawater in which the abundance of viruses, bacteria and grazers were reduced. High growth rates and frequency of dividing cells (FDCs) were recorded in 0.2-mm filtered treatments while growth was inhibited in incubations with a high proportion of virus-free ultrafiltered water. In two subsequent experiments using Mediterranean Sea populations, a two-point dilution approach in which viral abundance was reduced by 80-90% yielded similar results, and showed that Synechococcus only grew well in the presence of viruses, bacteria and grazers. In four further Mediterranean experiments viruses removed via ultrafiltration were added back, either untreated, or inactivated by a heat treatment. Growth rates and FDCs were higher in the presence of untreated viruses than with viruses inactivated by heat, suggesting that it was not organic matter in the virus-size fraction but rather the presence of infectious viruses which sustained growth. While Synechococcus was also infected by viruses during these experiments, our data imply that growth of Synechococcus may depend upon viral lysis of heterotrophic bacteria. This finding is consistent with the view that nutrient cycling by viral lysis of heterotrophic bacteria may control phytoplankton growth and ecosystem scale carbon production.

Šimek K, Comerma M, García JC, Nedoma J, Marcé R, Armengol J. 2011: The effect of river water circulation on the distribution and functioning of reservoir microbial communities as determined by a relative distance approach. Ecosystems 14:1-14.

The effect of river water quality, its inflow rate, and temperature on planktonic food web composition and activities were studied in the eutrophic Sau Reservoir (Catalonia, NE Spain). We analyzed 8 longitudinal transects conducted between July 1996 and April 1999 covering a wide range of variability in both seasonal and spatial circulation patterns. To compare objectively the biological longitudinal gradients under seasonally fluctuating water levels and different types of water circulation patterns, we applied a model based on the relative distance of a sampling station from the river inflow. Even under different hydrological scenarios, the model was able to characterize epilimnetic food chain successions and locations of peaks of bacteria, heterotrophic nanoflagellates, ciliates, phytoplankton, and zooplankton along the longitudinal gradient. The amplitude of microbial peaks was directly related to the proportion of nutrient and organic carbon rich river water that mixed into the reservoir epilimnion. Enhanced abundances and activities of microbes were detected in spring and summer periods, mainly during events of river water overflow when a large proportion of the river was directly mixed into the epilimnion. Thus, the relative input of river water is suggested to be a useful predictor of the amplitude of the development of the epilimnetic microbial food webs in highly loaded canyon-shaped reservoirs. These results may have important implications in the context of global change in Mediterranean regions, where expected reductions in runoff may profoundly affect river water circulation patterns in reservoirs and hence organic carbon cycling in these ecosystems.

Šimek K, Kasalický V, Jezbera J, Jezberová J, Hejzlar J., Hahn MW. 2010: Broad habitat range of the phylogenetically narrow R-BT065 cluster representing a core group of the betaproteobacterial genus Limnohabitans. Appl Environ Microbiol 76: 631-639

The distribution of the phylogenetically narrow R-BT065 cluster (Betaproteobacteria) in 102 freshwater lakes, reservoirs, and various ponds located in central Europe (a total of 122 samples) was examined by using a cluster-specific fluorescence in situ hybridization probe. These habitats differ markedly in pH, conductivity,trophic status, surface area, altitude, bedrock type, and other limnological characteristics. Despite the broad ecological diversity of the habitats investigated, the cluster was detected in 96.7% of the systems, and its occurrence was not restricted to a certain habitat type. However, the relative proportions of the cluster in the total bacterioplankton were significantly lower in humic and acidified lakes than in pH-neutral or alkaline habitats. On average, the cluster accounted for 9.4% of the total bacterioplankton (range, 0 to 29%). The relative abundance and absolute abundance of these bacteria were significantly and positively related to higher pH, conductivity, and the proportion of low-molecular-weight compounds in dissolved organic carbon (DOC) and negatively related to the total DOC and dissolved aromatic carbon contents. Together, these parameters explained 55.3% of the variability in the occurrence of the cluster. Surprisingly, no clear relationship of the R-BT065 bacteria to factors indicating the trophic status of habitats (i.e., different forms of phosphorus and chlorophyll a content) was found. Based on our results and previously published data, we concluded that the R-BT065 cluster represents a ubiquitous, highly active segment of bacterioplankton in nonacidic lakes and ponds and that alga-derived substrates likely form the main pool of substrates responsible for its high growth potential and broad distribution in freshwater habitats.

Šimek K, Kasalický V, Horňák K, Hahn MW, Weinbauer MG. 2010: Assessing niche separation in coexisting Limnohabitans strains through interactions with a competitor, viruses, and a bacterivore. Appl Environ Microbiol 76: 1406–1416

We investigated potential niche separation in two closely related (99.1% 16S rRNA gene sequence similarity) syntopic bacterial strains affiliated with the R-BT065 cluster, which represents a subgroup of the genus Limnohabitans. The two strains, designated B4 and D5, were isolated concurrently from a freshwater reservoir. Differences between the strains were examined through monitoring interactions with a bacterial competitor, Flectobacillus sp. (FL), and virus- and predator-induced mortality. Batch-type cocultures, designated B4+FL and D5+FL, were initiated with a similar biomass ratio among the strains. The proportion of each cell type present in the cocultures was monitored based on clear differences in cell sizes. Following exponential growth for 28 h, the cocultures were amended by the addition of two different concentrations of live or heat-inactivated viruses concentrated from the reservoir. Half of virus-amended treatments were inoculated immediately with an axenic flagellate predator, Poterioochromonas sp. The presence of the predator, of live viruses, and of competition between the strains significantly affected their population dynamics in the experimentally manipulated treatments. While strains B4 and FL appeared vulnerable to environmental viruses, strain D5 did not. Predator-induced mortality had the greatest impact on FL, followed by that on D5 and then B4. The virus-vulnerable B4 strain had smaller cells and lower biomass yield, but it was less subject to grazing. In contrast, the seemingly virus-resistant D5, with slightly larger grazing-vulnerable cells, was competitive with FL. Overall, our data suggest contrasting ecophysiological capabilities and partial niche separation in two coexisting Limnohabitans strains.

Znachor P,  Nedoma J. 2010: Importance of dissolved organic carbon for phytoplankton nutrition in a eutrophic reservoir. J Plankt Res 32: 367–376

In July–September 2007 at monthly intervals, we performed 4 experiments with size-fractionated phytoplankton organic carbon uptake in a eutrophic Římov Reservoir (Czech Republic). Along with primary production measurement, samples from surface and euphotic depth were incubated at in situ depths in light and dark bottles arrangement with 3H-labelled amino acid mixture and glucose in nanomolar concentrations. Moreover, we measured silica deposition and chlorophyll content in diatom cells without and with unlabelled glucose addition (100 µM). Phytoplankton uptake of both glucose and amino acids was low regardless the incubation depth. The major portion of incorporated organic carbon was found in fraction <2 µm indicating that bacteria are superior competitors for organic substrate than phytoplankton. Additionally, direct visualization of organic carbon uptake using a microautoradiography showed that bacteria attached on the phytoplankton accounted for the activity in large size fractions. Thus, mixotrophic nutrition of the phytoplankton was of low importance under natural conditions. However, glucose addition in micromolar concentrations resulted in a significant increase in diatom silification rates in a light bottle variant. Interestingly, in both light and dark bottles, chlorophyll fluorescence in diatom cells markedly decreased after the glucose addition indicating a potential restructuring of cell metabolism to benefit from a remarkably high concentration of available organic carbon in the environment.

Kaštovský J, Hauer T, Mareš J, Krautová M, Bešta T, Komárek J, Desortová B, Heteša J, Hindáková A, Houk V, Janeček E, Kopp R, Marvan P, Pumann P, Skácelová O, Zapomělová E. 2010: A review of the alien and expansive species of freshwater cyanobacteria and algae in the Czech Republic. Biol Invasions 12: 3599–3625

The invasion and spread of non-native species of many different kinds of organisms is of increasing interest to researchers. Invasions by microscopic organisms, however, are poorly understood, and their impact on the environment is probably underestimated. We collected available data on nonnative and invasive/expansive algae and cyanobacteria in the Czech Republic; we mapped their distribution and assessed their impact on local species and other real or potential risks resulting from their spread. The list of alien species in the Czech Republic contains 10 species of cyanobacteria, 9 species of Bacillariophyceae, 1 species of Dinophyceae, 1 species of Ulvo phyceae, 2 species of Chlorophyceae, and 1 species complex of Zygnematopyceae. The literature on the worldwide occurrence of these taxa is also reviewed.

Komárek J, Zapomělová E, Hindák F. 2010: Cronbergia, a new cyanobacterial genus (Cyanophyta) with special strategy of heterocyte formation. Cryptogamie Algologie 31: 331–341

We describe a new genus Cronbergia on the basis of a particular type of heterocyte fromation. This pattern consists in the division of one cell into two heterocytes followed by the break of the filament at the junction between the two heterocytes. The resulting trichomes have solitary heterocytes in the terminal position. Similar heterocyte development is only known in the genus Anabaenopsis, but the process of their formation is different. The strains / samples that correspond to this heterocyte formation and are included in the new genus are: (1) one strain (SAG B11.82) identified as Anabaena siamensis, but later assigned to the genus Richelia by Hindák (2003), (2) two natural populations from Slovak waters, (3) Cylindrospermum planctonicum from a Swedish fjord and (4) Cylindrospermum sp. strain PCC 7417. These four strains / samples were assigned to the new species Cronbergia siamensis, C. paucicellularis, C. planctonica and Cronbergia sp., respectively. The morphological differences between the four species are lengths and numbers of cells, and form and position of akinetes in filaments. The morphological differences of the new genus from Cylindrospermum, Richelia, Anabaenopsis, Cylindrospermopsis, Nostoc and Anabaena are also discussed. When available, the 16S rRNA sequences were compared with the one of the strain Cronbergia siamensis SAG B11.82, and showed that the strains of the new genus had at least 3% 16S rRNA divergence with them.

Komárková J, Jezberová J, Komárek O, Zapomělová E. 2010: Variability of Chroococcus (Cyanobacteria) morphospecies with regard to phylogenetic relationships. Hydrobiologia 639: 69–83

Recent advances in the taxonomy of cyanobacteria due to the utilization of molecular methods (such as 16S rRNA analysis) require a comparison of genetically identified items with their morphological expression. Morphological variability of seven monoclonal populations of the planktonic coccoid genus Chroococcus nägeli, isolated mostly from reservoirs, fishponds, and littoral substrata from localities in the Czech and Slovak Republics, were studied experimentally under various combinations of nutrient concentration, light intensity, temperature, and water movement. Two cultivation media (WHWC and BG11) commonly used in algal collections were applied in a liquid state. Of these, the WH medium was found to be more convenient for planktonic forms. Impacts of combined temperature and light gradients, concentration of P–PO4, and a stable versus shaken medium were found to stress different morphological modifications as a consequence of varied growth intensity and media convenience. Cell width was chosen as the parameter for testing changes in morphology; formation of mucilage and packets of cells were also taken into account. According to 16S rRNA gene analysis, the sequences of 10 strains (including seven studied in the experiments), which were assigned to the genus Chroococcus in the Culture Collection CCALA Třeboň (www.cas.ccala.cz) formed four distinct phylogenetic groups. While two of them showed no affiliation to the genus Chroococcus, two other groups proved the polyphyletic character of the genus. Apart from the group of typical species of the genus Chroococcus, a group of planktonic species could be distinguished, i.e., Chroococcus limneticus Lemmermann 1898 (Limnococcus), and was established as a new genus after recombination.

Zapomělová E, Řeháková K, Jezberová J, Komárková J. 2010: Polyphasic characterization of eight planktonic Anabaena strains (Cyanobacteria) with reference to the variability of 61 Anabaena populations observed in the field. Hydrobiologia 639: 99–113

The plasticity of morphological features used for single morphospecies identification was studied under varied experimental conditions (temperature, light, nitrogen, phosphorus) in eight planktonic Anabaena strains. The strains represented all of the morphospecies with coiled trichomes commonly occurring in Central Europe (two strains of A. mendotae & A. sigmoidea complex, two A. lemmermannii strains, two A. flos-aquae strains, and two strains of A. circinalis & A. crassa complex). Significant effects of the growth conditions on vegetative cell dimensions were observed in seven strains, and P concentration was the main influencing factor in most cases (six strains). Significant effect of an environmental factor (P) on akinete morphology was found in only one strain. Experimentally assessed temperature and light growth optima were specific for each strain and were not consistent with the taxonomic affiliation of the strains. Morphologies of the Anabaena strains studied were compared with the field morphologies of 61 Anabaena populations of eight morphospecies observed in the Czech Republic. The range of morphological variability of single strains under the experimental conditions spanned the total variability of the populations of relevant morphospecies observed in the field. Delimitations and proper descriptions of the morphospecies are discussed in the light of partial 16S rRNA gene sequences of the studied strains.

Horňák K, Jezbera J, Šimek K. 2010 Bacterial single-cell activities along the nutrient availability gradient in a canyon-shaped reservoir: a seasonal study. Aquat Microb Ecol 60:215–225 (Open Access article, http://www.int-res.com/articles/ame_oa/a060p215.pdf)

We investigated the linkages between the composition and the activities of bacterioplankton assemblages in the meso-eutrophic Římov reservoir (Czech Republic). We examined bacterial fractions with visible leucine and glucose incorporation using microautoradiography, and proportions of bacteria with an intact membrane (live), high nucleic acid (HNA) and low nucleic acid (LNA) content, and an active electron transport system (CTC+ cells; CTC is 5-cyano-2,3-ditolyl-tetrazolium chloride) by flow cytometry. Three stations along the longitudinal axis of the reservoir (designated Dam, Middle, and River) with contrasting phosphorus concentrations and bacterial and extracellular phytoplankton production were sampled at intervals of 3 wk from 29 March to 15 November 2005. At all stations, Betaproteobacteria (BET) or Actinobacteria (ACT) dominated the bacterial community composition, while Cytophaga-Flavobacteria (CF) accounted for smaller proportions. ACT showed high proportions of cells incorporating both leucine and glucose in all samples, whereas only small fractions of CF were scored positive for the incorporation of these substrates. BET incorporated leucine preferentially to glucose in all samples. We identified bacterial phylogenetic groups that correlated with different bacterial populations as determined by flow cytometry: CF and BET significantly contributed to the pool of HNA cells at Stn River, whereas the opposite was found for ACT, forming the pool of LNA cells at all stations. Since ACT efficiently incorporated organic substrates, the LNA fraction represented a highly active component of bacterial assemblages. At Stns Dam and Middle, the dynamics of CF also correlated with the population of CTC+ cells and an extracellular phytoplankton production.

Sirová D, Borovec J, Šantrůčková H, Šantrůček J, Vrba J, Adamec L. 2010: Utricularia carnivory revisited: plants supply photosynthetic carbon to traps. J Exp Bot 61: 99–103

The rootless, aquatic Utricularia species belong to the largest and most cosmopolitan carnivorous plant genus. Populations of Utricularia plants are an important component of many standing, nutrient-poor, and humic waters. Carbon (C) allocation is an aspect of Utricularia’s ecophysiology that has not been studied previously and there is considerable uncertainty about the functional and ecological benefit of the trap-associated microbial community and the potential role played by C exudation in enhancing plant–microbe interactions. A 13C-labelling experiment was conducted in greenhouse conditions to determine the C allocation between plant tissues of increasing age and trap fluid in two Utricularia species. Both species allocated a majority of the newly fixed C into the fast growing shoot apex (46.1±8.6% in U. vulgaris and 56.1% in U. australis). Carbon allocation rapidly decreased with increasing age of the shoot, constituting only 8.0±4.0% and 6.7% of the total newly fixed C in the oldest analysed segments in U. vulgaris and U. australis, respectively. In the trap-bearing shoot segments, the ratio of C exuded into the trap fluid to that in plant tissues increased markedly with age—in the oldest analysed segments twice as much newly fixed C was allocated into the trap fluid than the plant tissue. Overall, a significant amount of the newly fixed C, approximately 25% (U. vulgaris) and 20% (U. australis), was allocated to the trap fluid. The importance of C exudation for the development of the microbial community associated with the traps as well as for the growth and ecology of aquatic Utricularia is discussed. 

Adamec L, Sirová D, Vrba J, Rejmánková E. 2010: Enzyme production in the traps of aquatic Utricularia species. Biologia 65: 273–278

We studied the influence of habitat and increased mineral phosphorus and nitrogen loading on the extracellular activity of five selected hydrolases and pH in the trap fluid of the aquatic carnivorous plants, Utricularia vulgaris, U. australis, and U. foliosa (Lentibulariaceae). Enzyme activities in the trap fluid were determined using fluorometry. Phosphatase exhibited the highest activities in the traps of the European species as well as field-grown tropical U. foliosa. Trap enzyme production appeared to be uninfluenced by elevated dissolved mineral N or P concentrations both in the trap and ambient environment and thus, it seems to be constitutive. Enzyme activity in the trap fluid was determined by species and environmental conditions and varied significantly among sites within a single species. Trap fluid pH was between 4.2–5.1 in U. vulgaris and U. australis but between 5.7–7.3 in U. foliosa and seems to be regulated by the traps.

Adamec L, Sirová D, Vrba J. 2010: Contrasting growth effect of prey capture in two aquatic carnivorous plant species. Fundam Appl Limnol 176: 153–160

A detailed 11-day growth analysis was performed under greenhouse conditions on two aquatic, carnivorous plants in order to determine growth effects caused by supplemental feeding on zooplankton. The two species surveyed were the rare, stenotypic Aldrovanda vesiculosa and the more common, eurytopic Utricularia australis. While a highly significant increase in shoot biomass (by 60 %) was found for Aldrovanda plants supplemented with prey, no significant effect of prey addition occurred in Utricularia. However, main shoots of fed plants of both species were significantly longer, had more mature leaf nodes, and their mean apical growth rate was higher than in unfed plants. Branching was markedly supported by pre