bacterivorous
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Heterotrophic nanoflagellates (HNF) are considered as major planktonic bacterivores, however, larger HNF taxa can also be important predators of eukaryotes. To examine this trophic cascading, natural protistan communities from a freshwater reservoir were released from grazing pressure by zooplankton via filtration through 10- and 5-µm filters, yielding microbial food webs of different complexity. Protistan growth was stimulated by amendments of five Limnohabitans strains, thus yielding five prey-specific treatments distinctly modulating protistan communities in 10- versus 5-µm fractions. HNF dynamics was tracked by applying five eukaryotic fluorescence in situ hybridization probes covering 55-90% of total flagellates. During the first experimental part, mainly small bacterivorous Cryptophyceae prevailed, with significantly higher abundances in 5-µm treatments. Larger predatory flagellates affiliating with Katablepharidacea and one Cercozoan lineage (increasing to up to 28% of total HNF) proliferated towards the experimental endpoint, having obviously small phagocytized HNF in their food vacuoles. These predatory flagellates reached higher abundances in 10-µm treatments, where small ciliate predators and flagellate hunters also (Urotricha spp., Balanion planctonicum) dominated the ciliate assemblage. Overall, our study reports pronounced cascading effects from bacteria to bacterivorous HNF, predatory HNF and ciliates in highly treatment-specific fashions, defined by both prey-food characteristics and feeding modes of predominating protists.
- MeSH
- Cercozoa * MeSH
- Cryptophyta MeSH
- hybridizace in situ fluorescenční MeSH
- potravní řetězec * MeSH
- sladká voda MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Small bacterivorous eukaryotes play a cardinal role in aquatic food webs and their taxonomic classification is currently a hot topic in aquatic microbial ecology. Despite increasing interest in their diversity, core questions regarding predator-prey specificity remain largely unanswered, e.g., which heterotrophic nanoflagellates (HNFs) are the main bacterivores in freshwaters and which prokaryotes support the growth of small HNFs. To answer these questions, we fed natural communities of HNFs from Římov reservoir (Czech Republic) with five different bacterial strains of the ubiquitous betaproteobacterial genera Polynucleobacter and Limnohabitans. We combined amplicon sequencing and catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) targeting eukaryotic 18 S rRNA genes to track specific responses of the natural HNF community to prey amendments. While amplicon sequencing provided valuable qualitative data and a basis for designing specific probes, the number of reads was insufficient to accurately quantify certain eukaryotic groups. We also applied a double-hybridization technique that allows simultaneous phylogenetic identification of both predator and prey. Our results show that community composition of HNFs is strongly dependent upon prey type. Surprisingly, Cryptophyta were the most abundant bacterivores, although this phylum has been so far assumed to be mainly autotrophic. Moreover, the growth of a small lineage of Cryptophyta (CRY1 clade) was strongly stimulated by one Limnohabitans strain in our experiment. Thus, our study is the first report that colorless Cryptophyta are major bacterivores in summer plankton samples and can play a key role in the carbon transfer from prokaryotes to higher trophic levels.
- MeSH
- Bacteria klasifikace genetika izolace a purifikace metabolismus MeSH
- Cryptophyta mikrobiologie MeSH
- fylogeneze MeSH
- heterotrofní procesy MeSH
- hybridizace in situ fluorescenční MeSH
- plankton mikrobiologie MeSH
- potravní řetězec MeSH
- roční období MeSH
- sladká voda mikrobiologie parazitologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
High-elevation cold deserts in Tibet and Himalaya are one of the most extreme environments. One consequence is that the diversity of macrofauna in this environment is often limited, and soil microorganisms have a more influential role in governing key surface and subsurface bioprocesses. High-elevation soil microfauna represent important components of cold ecosystems and dominant consumers of microbial communities. Still little is known about their diversity and distribution on the edge of their reproductive and metabolic abilities. In this study, we disentangle the impact of elevation and soil chemistry on diversity and distribution of rotifers, nematodes and tardigrades and their most frequent feeding strategies (microbial filter-feeders, bacterivores, fungivores, root-fungal feeders, omnivores) along two contrasting altitudinal gradients in Indian NW Himalaya (Zanskar transect from 3805 to 4714 m a.s.l.) and southwestern Tibet (Tso Moriri transect from 4477 to 6176 m a.s.l.), using a combination of multivariate analysis, variation partitioning and generalized additive models. Zanskar transect had higher precipitation, soil moisture, organic matter and available nutrients than dry Tso Moriri transect. In total, 40 species of nematodes, 19 rotifers and 1 tardigrade were discovered. Species richness and total abundance of rotifers and nematodes showed mid-elevation peaks in both investigated transects. The optimum for rotifers was found at higher elevation than for nematodes. Diversity and distribution of soil microfauna was best explained by soil nitrogen, phosphorus and organic matter. More fertile soils hosted more diverse and abundant faunal communities. In Tso Moriri, bacterivores represented 60% of all nematodes, fungivores 35%, root-fungal feeders 1% and omnivores 3%. For Zanskar the respective proportions were 21%, 13%, 56% and 9%. Elevational optima of different feeding strategies occurred in Zanskar in one elevation zone (4400-4500 m), while in Tso Moriri each feeding strategy had their unique optima with fungivores at 5300 m (steppes), bacterivores at 5500 m (alpine grassland), filter-feeders at 5600 m and predators and omnivores above 5700 m (subnival zone). Our results shed light on the diversity of microfauna in the high-elevation cold deserts and disentangle the role of different ecological filters in structuring microfaunal communities in the rapidly-warming Himalayas.
- MeSH
- Bacteria klasifikace izolace a purifikace MeSH
- biodiverzita * MeSH
- ekosystém * MeSH
- houby klasifikace izolace a purifikace MeSH
- nadmořská výška * MeSH
- nízká teplota * MeSH
- půda MeSH
- Publikační typ
- časopisecké články MeSH
- Geografické názvy
- Nepál MeSH
- Tibet MeSH
The genus Tetrahymena (Ciliophora, Oligohymenophorea) probably represents the best studied ciliate genus. At present, more than forty species have been described. All are colorless, i.e. they do not harbor symbiotic algae, and as aerobes they need at least microaerobic habitats. Here, we present the morphological and molecular description of the first green representative, Tetrahymena utriculariae n. sp., living in symbiosis with endosymbiotic algae identified as Micractinium sp. (Chlorophyta). The full life cycle of the ciliate species is documented, including trophonts and theronts, conjugating cells, resting cysts and dividers. This species has been discovered in an exotic habitat, namely in traps of the carnivorous aquatic plant Utricularia reflexa (originating from Okavango Delta, Botswana). Green ciliates live as commensals of the plant in this anoxic habitat. Ciliates are bacterivorous, however, symbiosis with algae is needed to satisfy cell metabolism but also to gain oxygen from symbionts. When ciliates are cultivated outside their natural habitat under aerobic conditions and fed with saturating bacterial food, they gradually become aposymbiotic. Based on phylogenetic analyses of 18S rRNA and mitochondrial cox1 genes T. utriculariae forms a sister group to Tetrahymena thermophila.
- MeSH
- cévnaté rostliny parazitologie MeSH
- Chlorophyta parazitologie MeSH
- Ciliophora klasifikace metabolismus fyziologie MeSH
- ekologie MeSH
- ekosystém MeSH
- fylogeneze * MeSH
- kyslík metabolismus MeSH
- mitochondrie genetika MeSH
- Oligohymenophorea klasifikace MeSH
- protozoální DNA MeSH
- RNA ribozomální 18S genetika MeSH
- rostliny parazitologie MeSH
- sekvence nukleotidů MeSH
- stadia vývoje MeSH
- symbióza fyziologie MeSH
- Tetrahymena thermophila klasifikace genetika MeSH
- Tetrahymena klasifikace cytologie izolace a purifikace metabolismus MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
Trap fluid of aquatic carnivorous plants of the genus Utricularia hosts specific microbiomes consisting of commensal pro- and eukaryotes of largely unknown ecology. We examined the characteristics and dynamics of bacteria and the three dominant eukaryotes, i.e. the algae-bearing ciliate Tetrahymena utriculariae (Ciliophora), a green flagellate Euglena agilis (Euglenophyta), and the alga Scenedesmus alternans (Chlorophyta), associated with the traps of Utricularia reflexa. Our study focused on ecological traits and life strategies of the highly abundant ciliate whose biomass by far exceeds that of other eukaryotes and bacteria independent of the trap age. The ciliate was the only bacterivore in the traps, driving rapid turnover of bacterial standing stock. However, given the large size of the ciliate and the cell-specific uptake rates of bacteria we estimated that bacterivory alone would likely be insufficient to support its apparent rapid growth in traps. We suggest that mixotrophy based on algal symbionts contributes significantly to the diet and survival strategy of the ciliate in the extreme (anaerobic, low pH) trap-fluid environment. We propose a revised concept of major microbial interactions in the trap fluid where ciliate bacterivory plays a central role in regeneration of nutrients bound in rapidly growing bacterial biomass.
- MeSH
- anaerobióza MeSH
- Bacteria MeSH
- biomasa MeSH
- Chlorophyta MeSH
- Ciliophora fyziologie MeSH
- ekologie * MeSH
- koncentrace vodíkových iontů MeSH
- Magnoliopsida chemie růst a vývoj mikrobiologie parazitologie MeSH
- mikrobiální společenstva MeSH
- stadia vývoje MeSH
- symbióza fyziologie MeSH
- Tetrahymena růst a vývoj fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
The competitive strength of four cosmopolitan freshwater betaproteobacterial isolates was investigated in the presence or absence of bacterivorous flagellates during continuous cultivation in artificial minimal medium at two dilution rates. Bacteria reached similar abundance and growth rate in monocultures, but in co-cultures, two strains (Acidovorax sp. and Massilia sp.) displayed significantly higher numbers and growth rates. These potential cross-feeding benefits were also supported by a high nutritional versatility of the two strains. In contrast, Hydrogenophaga sp. was seemingly less competitive or even inhibited by co-cultivation, and Limnohabitans planktonicus displayed striking abundance fluctuations. The latter two strains were least versatile in the uptake of different carbon sources and thus suffered more from interspecific competition. Moreover, remarkable strain-specific responses appeared when bacteria experienced increasing loss rates due to grazing and/or raised dilution rates. Limnohabitans planktonicus developed no successful defence strategy and was close to extinction. Massilia sp. formed grazing-resistant filaments exclusively at low dilution, but was highly reduced at increased flow-through. Acidovorax sp. was selectively ingested, but compensated grazing losses with accelerated growth rates and formed (co-)aggregates together with Hydrogenophaga sp. to escape predation at high flow-through. These species-specific interactions, growth responses and defence strategies strongly modulate mixed microbial assemblages and the microbial food web.
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.
- MeSH
- Actinobacteria fyziologie MeSH
- Burkholderiaceae fyziologie MeSH
- časové faktory MeSH
- Comamonadaceae fyziologie MeSH
- Eukaryota růst a vývoj metabolismus fyziologie MeSH
- fyziologie bakterií MeSH
- geny rRNA genetika MeSH
- heterotrofní procesy MeSH
- potravní řetězec MeSH
- sladká voda mikrobiologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
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.
