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Viral community analysis in a marine oxygen minimum zone indicates increased potential for viral manipulation of microbial physiological state. THE ISME JOURNAL 2022; 16:972-982. [PMID: 34743175 PMCID: PMC8940887 DOI: 10.1038/s41396-021-01143-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 10/11/2021] [Accepted: 10/13/2021] [Indexed: 11/08/2022]
Abstract
Microbial communities in oxygen minimum zones (OMZs) are known to have significant impacts on global biogeochemical cycles, but viral influence on microbial processes in these regions are much less studied. Here we provide baseline ecological patterns using microscopy and viral metagenomics from the Eastern Tropical North Pacific (ETNP) OMZ region that enhance our understanding of viruses in these climate-critical systems. While extracellular viral abundance decreased below the oxycline, viral diversity and lytic infection frequency remained high within the OMZ, demonstrating that viral influences on microbial communities were still substantial without the detectable presence of oxygen. Viral community composition was strongly related to oxygen concentration, with viral populations in low-oxygen portions of the water column being distinct from their surface layer counterparts. However, this divergence was not accompanied by the expected differences in viral-encoded auxiliary metabolic genes (AMGs) relating to nitrogen and sulfur metabolisms that are known to be performed by microbial communities in these low-oxygen and anoxic regions. Instead, several abundant AMGs were identified in the oxycline and OMZ that may modulate host responses to low-oxygen stress. We hypothesize that this is due to selection for viral-encoded genes that influence host survivability rather than modulating host metabolic reactions within the ETNP OMZ. Together, this study shows that viruses are not only diverse throughout the water column in the ETNP, including the OMZ, but their infection of microorganisms has the potential to alter host physiological state within these biogeochemically important regions of the ocean.
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2
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Pascelli C, Laffy PW, Kupresanin M, Ravasi T, Webster NS. Morphological characterization of virus-like particles in coral reef sponges. PeerJ 2018; 6:e5625. [PMID: 30356950 PMCID: PMC6195793 DOI: 10.7717/peerj.5625] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Accepted: 08/22/2018] [Indexed: 12/03/2022] Open
Abstract
Marine sponges host complex microbial consortia that vary in their abundance, diversity and stability amongst host species. While our understanding of sponge-microbe interactions has dramatically increased over the past decade, little is known about how sponges and their microbial symbionts interact with viruses, the most abundant entities in the ocean. In this study, we employed three transmission electron microscopy (TEM) preparation methods to provide the first comprehensive morphological assessment of sponge-associated viruses. The combined approaches revealed 50 different morphologies of viral-like particles (VLPs) represented across the different sponge species. VLPs were visualized within sponge cells, within the sponge extracellular mesohyl matrix, on the sponge ectoderm and within sponge-associated microbes. Non-enveloped, non-tailed icosahedral VLPs were the most commonly observed morphotypes, although tailed bacteriophage, brick-shaped, geminate and filamentous VLPs were also detected. Visualization of sponge-associated viruses using TEM has confirmed that sponges harbor not only diverse communities of microorganisms but also diverse communities of viruses.
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Affiliation(s)
- Cecília Pascelli
- Australian Institute of Marine Science, Townsville, Queensland, Australia.,James Cook University, Townsville, Queensland, Australia.,AIMS@JCU, Australian Institute of Marine Science and James Cook University, Townsville, Queensland, Australia
| | - Patrick W Laffy
- Australian Institute of Marine Science, Townsville, Queensland, Australia
| | - Marija Kupresanin
- KAUST Environmental Epigenetic Program (KEEP), Division of Biological and Environmental Sciences & Engineering, King Abdullah University of Science and Technology, Thuwal, Kingdom of Saudi Arabia
| | - Timothy Ravasi
- KAUST Environmental Epigenetic Program (KEEP), Division of Biological and Environmental Sciences & Engineering, King Abdullah University of Science and Technology, Thuwal, Kingdom of Saudi Arabia
| | - Nicole S Webster
- Australian Institute of Marine Science, Townsville, Queensland, Australia.,AIMS@JCU, Australian Institute of Marine Science and James Cook University, Townsville, Queensland, Australia.,Australian Centre for Ecogenomics, University of Queensland, Brisbane, Queensland, Australia
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3
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Knowles B, Bailey B, Boling L, Breitbart M, Cobián-Güemes A, Del Campo J, Edwards R, Felts B, Grasis J, Haas AF, Katira P, Kelly LW, Luque A, Nulton J, Paul L, Peters G, Robinett N, Sandin S, Segall A, Silveira C, Youle M, Rohwer F. Variability and host density independence in inductions-based estimates of environmental lysogeny. Nat Microbiol 2017; 2:17064. [PMID: 28452987 DOI: 10.1038/nmicrobiol.2017.64] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Accepted: 03/22/2017] [Indexed: 11/09/2022]
Abstract
Temperate bacterial viruses (phages) may enter a symbiosis with their host cell, forming a unit called a lysogen. Infection and viral replication are disassociated in lysogens until an induction event such as DNA damage occurs, triggering viral-mediated lysis. The lysogen-lytic viral reproduction switch is central to viral ecology, with diverse ecosystem impacts. It has been argued that lysogeny is favoured in phages at low host densities. This paradigm is based on the fraction of chemically inducible cells (FCIC) lysogeny proxy determined using DNA-damaging mitomycin C inductions. Contrary to the established paradigm, a survey of 39 inductions publications found FCIC to be highly variable and pervasively insensitive to bacterial host density at global, within-environment and within-study levels. Attempts to determine the source(s) of variability highlighted the inherent complications in using the FCIC proxy in mixed communities, including dissociation between rates of lysogeny and FCIC values. Ultimately, FCIC studies do not provide robust measures of lysogeny or consistent evidence of either positive or negative host density dependence to the lytic-lysogenic switch. Other metrics are therefore needed to understand the drivers of the lytic-lysogenic decision in viral communities and to test models of the host density-dependent viral lytic-lysogenic switch.
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Affiliation(s)
- Ben Knowles
- Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Barbara Bailey
- Department of Mathematics and Statistics, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Lance Boling
- Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Mya Breitbart
- College of Marine Science, University of South Florida, 140 Seventh Avenue South, St Petersburg, Florida 33701, USA
| | - Ana Cobián-Güemes
- Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Javier Del Campo
- Department of Botany, University of British Columbia, 3529-6270 University Boulevard, Vancouver, British Columbia V6T 1Z4, Canada
| | - Rob Edwards
- Computational Science Research Center, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA.,Department of Computer Science, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA.,Viral Information Institute, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Ben Felts
- Department of Mathematics and Statistics, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Juris Grasis
- Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Andreas F Haas
- Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Parag Katira
- Department of Mechanical Engineering, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Linda Wegley Kelly
- Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Antoni Luque
- Department of Mathematics and Statistics, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA.,Computational Science Research Center, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA.,Viral Information Institute, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Jim Nulton
- Department of Mathematics and Statistics, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Lauren Paul
- Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Gregory Peters
- Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Nate Robinett
- Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Stuart Sandin
- Scripps Institution of Oceanography, University of California San Diego, 950 Gilman Drive, California 92903, USA
| | - Anca Segall
- Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA.,Viral Information Institute, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | - Cynthia Silveira
- Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
| | | | - Forest Rohwer
- Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA.,Viral Information Institute, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
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4
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Colombet J, Robin A, Sime-Ngando T. Genotypic, size and morphological diversity of virioplankton in a deep oligomesotrophic freshwater lake (Lac Pavin, France). J Environ Sci (China) 2017; 53:48-59. [PMID: 28372760 DOI: 10.1016/j.jes.2016.05.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Revised: 05/02/2016] [Accepted: 05/05/2016] [Indexed: 06/07/2023]
Abstract
We examined changes in morphological and genomic diversities of viruses by means of transmission electronic microscopy and pulsed field gel electrophoresis (PFGE) over a nine-month period (April-December 2005) at four different depths in the oligomesotrophic Lac Pavin. We found that the majority of viruses in this lake belonged to the family of Siphoviridae or were untailed, with capsid sizes ranging from 30 to 60nm, and exhibited genome sizes ranging from 15 to 45kb. On average, 12 different genotypes dominated each of the PFGE fingerprints. The highest genomic viral richness was recorded in summer (mean=14 bands per PFGE fingerprint) and in the epilimnion (mean=13 bands per PFGE fingerprint). Among the physico-chemical and biological variables considered, the availability of the hosts appeared to be the main factor regulating the variations in the viral diversity.
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Affiliation(s)
- Jonathan Colombet
- Laboratory Microorganisms: Genome and Environment, Clermont University Blaise Pascal, UMR CNRS 6023, 24 avenue des Landais, BP 80026, F-63171 Aubière, France.
| | - Agnès Robin
- CIRAD, UMR Eco&Sols, 2 place Viala, 34060 Montpellier Cedex 1, France
| | - Télesphore Sime-Ngando
- Laboratory Microorganisms: Genome and Environment, Clermont University Blaise Pascal, UMR CNRS 6023, 24 avenue des Landais, BP 80026, F-63171 Aubière, France
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5
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Elmahdy M, Fongaro G, Magri M, Petruccio M, Barardi C. Spatial distribution of enteric viruses and somatic coliphages in a Lagoon used as drinking water source and recreation in Southern Brazil. Int J Hyg Environ Health 2016; 219:617-625. [DOI: 10.1016/j.ijheh.2016.07.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Revised: 07/07/2016] [Accepted: 07/12/2016] [Indexed: 12/24/2022]
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6
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Buckalew DW, Tuono AJ, Simmons AK, Lankford TW, Smith DH. Homogeneous Distribution of <i>Escherichia coli</i> Measured within the Vertical Water Column of Small, Freshwater Streams. ACTA ACUST UNITED AC 2015. [DOI: 10.4236/jwarp.2015.75033] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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7
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Palesse S, Colombet J, Pradeep Ram AS, Sime-Ngando T. Linking host prokaryotic physiology to viral lifestyle dynamics in a temperate freshwater lake (Lake Pavin, France). MICROBIAL ECOLOGY 2014; 68:740-750. [PMID: 24910014 DOI: 10.1007/s00248-014-0441-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Accepted: 05/20/2014] [Indexed: 06/03/2023]
Abstract
In aquatic ecosystems, fluctuations in environmental conditions and prokaryotic host physiological states can strongly affect the dynamics of viral life strategies. The influence of prokaryote physiology and environmental factors on viral replication cycles (lytic and lysogeny) was investigated from April to September 2011 at three different strata (epi, meta, and hypolimnion) in the mixolimnion of deep volcanic temperate freshwater Lake Pavin (France). Overall, the euphotic region (epi and metalimnion) was more dynamic and showed significant variation in microbial standing stocks, prokaryotic physiological state, and viral life strategies compared to the aphotic hypolimnion which was stable within sampled months. The prokaryotic host physiology as inferred from the nucleic acid content of prokaryotic cells (high or low nucleic acid) was strongly regulated by the chlorophyll concentration. The predominance of the high nucleic acid (HNA) prokaryotes (cells) over low nucleic acid (LNA) prokaryotes (cells) in the spring (HNA/LNA = 1.2) and vice versa in the summer period (HNA/LNA = 0.4) suggest that the natural prokaryotic communities underwent major shifts in their physiological states during investigated time period. The increase in the percentage of inducible lysogenic prokaryotes in the summer period was associated with the switch in the dominance of LNA over HNA cells, which coincided with the periods of strong resource (nutrient) limitation. This supports the idea that lysogeny represents a maintenance strategy for viruses in unproductive or harsh nutrient/host conditions. A negative correlation of percentage of lysogenic prokaryotes with HNA cell abundance and chlorophyll suggest that lysogenic cycle is closely related to prokaryotic cells which are stressed or starved due to unavailability of resources for its growth and activity. Our results provide support to previous findings that changes in prokaryote physiology are critical for the promotion and establishment of lysogeny in aquatic ecosystems, which are prone to constant environmental fluctuations.
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Affiliation(s)
- S Palesse
- Laboratoire Microorganismes: Génome et Environnement, UMR CNRS 6023, Clermont Université, Université Blaise Pascal, BP 80026, 63171, Aubière Cedex, France
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8
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Hurwitz BL, Brum JR, Sullivan MB. Depth-stratified functional and taxonomic niche specialization in the 'core' and 'flexible' Pacific Ocean Virome. ISME JOURNAL 2014; 9:472-84. [PMID: 25093636 DOI: 10.1038/ismej.2014.143] [Citation(s) in RCA: 126] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2014] [Revised: 06/22/2014] [Accepted: 06/24/2014] [Indexed: 11/09/2022]
Abstract
Microbes drive myriad ecosystem processes, and their viruses modulate microbial-driven processes through mortality, horizontal gene transfer, and metabolic reprogramming by viral-encoded auxiliary metabolic genes (AMGs). However, our knowledge of viral roles in the oceans is primarily limited to surface waters. Here we assess the depth distribution of protein clusters (PCs) in the first large-scale quantitative viral metagenomic data set that spans much of the pelagic depth continuum (the Pacific Ocean Virome; POV). This established 'core' (180 PCs; one-third new to science) and 'flexible' (423K PCs) community gene sets, including niche-defining genes in the latter (385 and 170 PCs are exclusive and core to the photic and aphotic zones, respectively). Taxonomic annotation suggested that tailed phages are ubiquitous, but not abundant (<5% of PCs) and revealed depth-related taxonomic patterns. Functional annotation, coupled with extensive analyses to document non-viral DNA contamination, uncovered 32 new AMGs (9 core, 20 photic and 3 aphotic) that introduce ways in which viruses manipulate infected host metabolism, and parallel depth-stratified host adaptations (for example, photic zone genes for iron-sulphur cluster modulation for phage production, and aphotic zone genes for high-pressure deep-sea survival). Finally, significant vertical flux of photic zone viruses to the deep sea was detected, which is critical for interpreting depth-related patterns in nature. Beyond the ecological advances outlined here, this catalog of viral core, flexible and niche-defining genes provides a resource for future investigation into the organization, function and evolution of microbial molecular networks to mechanistically understand and model viral roles in the biosphere.
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Affiliation(s)
- Bonnie L Hurwitz
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA
| | - Jennifer R Brum
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA
| | - Matthew B Sullivan
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA
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9
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Sime-Ngando T. Environmental bacteriophages: viruses of microbes in aquatic ecosystems. Front Microbiol 2014; 5:355. [PMID: 25104950 PMCID: PMC4109441 DOI: 10.3389/fmicb.2014.00355] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Accepted: 06/25/2014] [Indexed: 11/29/2022] Open
Abstract
Since the discovery 2–3 decades ago that viruses of microbes are abundant in marine ecosystems, viral ecology has grown increasingly to reach the status of a full scientific discipline in environmental sciences. A dedicated ISVM society, the International Society for Viruses of Microorganisms, (http://www.isvm.org/) was recently launched. Increasing studies in viral ecology are sources of novel knowledge related to the biodiversity of living things, the functioning of ecosystems, and the evolution of the cellular world. This is because viruses are perhaps the most diverse, abundant, and ubiquitous biological entities in the biosphere, although local environmental conditions enrich for certain viral types through selective pressure. They exhibit various lifestyles that intimately depend on the deep-cellular mechanisms, and are ultimately replicated by members of all three domains of cellular life (Bacteria, Eukarya, Archaea), as well as by giant viruses of some eukaryotic cells. This establishes viral parasites as microbial killers but also as cell partners or metabolic manipulators in microbial ecology. The present chapter sought to review the literature on the diversity and functional roles of viruses of microbes in environmental microbiology, focusing primarily on prokaryotic viruses (i.e., phages) in aquatic ecosystems, which form the bulk of our knowledge in modern environmental viral ecology.
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Affiliation(s)
- Télesphore Sime-Ngando
- Laboratoire Microorganismes: Génome et Environnement, UMR CNRS 6023, Clermont Université Blaise Pascal Aubière, France
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10
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Oikonomou A, Pachiadaki M, Stoeck T. Protistan grazing in a meromictic freshwater lake with anoxic bottom water. FEMS Microbiol Ecol 2013; 87:691-703. [DOI: 10.1111/1574-6941.12257] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Revised: 10/29/2013] [Accepted: 11/13/2013] [Indexed: 01/26/2023] Open
Affiliation(s)
- Andreas Oikonomou
- Department of Ecology; University of Kaiserslautern; Kaiserslautern Germany
| | - Maria Pachiadaki
- Department of Ecology; University of Kaiserslautern; Kaiserslautern Germany
| | - Thorsten Stoeck
- Department of Ecology; University of Kaiserslautern; Kaiserslautern Germany
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11
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Ram ASP, Palesse S, Colombet J, Sabart M, Perriere F, Sime-Ngando T. Variable viral and grazer control of prokaryotic growth efficiency in temperate freshwater lakes (French Massif Central). MICROBIAL ECOLOGY 2013; 66:906-916. [PMID: 24061344 DOI: 10.1007/s00248-013-0289-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Accepted: 09/03/2013] [Indexed: 06/02/2023]
Abstract
The effects of viral lysis and heterotrophic nanoflagellate grazing (top down forces) on prokaryotic mortality and their subsequent impact on their metabolism were estimated in the upper euphotic and deeper aphotic depth of 11 freshwater lakes located in the French Massif Central. The standing stocks of viruses (VA) and heterotrophic nanoflagellate (HNF) varied significantly (p < 0.05) with sampled depth. VA was substantially (twofold on an average) and significantly higher (p < 0.03) at the aphotic compared to euphotic depth, whereas the reverse was true (p < 0.02) for HNF. Among the prokaryote subgroup, high nucleic acid content prokaryotes explained for significant variability in the total VA and served as principle host target for viral proliferation. Like standing stocks, flagellate grazing and viral infection rates also followed similar patterns. In the investigated lakes, the mechanism for regulating prokaryotic production varied with sampled depth from grazing control in the euphotic to control due to viral lysis in the aphotic. We also tested the hypothesis of top down control on prokaryotic growth efficiency (PGE, which we used as an index of prokaryotic physiological and energetic status at the community level) at both depths. Overall, among the studied lakes, PGE varied widely (4-51 %) with significantly (p < 0.05) lower values in the aphotic (mean = 18 ± 4 %) than euphotic depth (mean = 32 ± 9 %). Contrasting observations on the top down control of PGE between sampled depths were observed. The presence of grazers was found to stimulate PGE at the euphotic, whereas viruses through their lytic infection had a strong negative impact on PGE at the aphotic depth. Such observed differences in PGE and the mechanism controlling prokaryotic production with depth could eventually have strong implication on carbon and nutrient flux patterns in the studied lakes.
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Affiliation(s)
- A S Pradeep Ram
- Laboratoire Microorganismes: Génome et Environnement, UMR CNRS 6023, Clermont Université, Université Blaise Pascal, BP 80026, 63171, Aubiere Cedex, France,
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12
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Global morphological analysis of marine viruses shows minimal regional variation and dominance of non-tailed viruses. ISME JOURNAL 2013; 7:1738-51. [PMID: 23635867 DOI: 10.1038/ismej.2013.67] [Citation(s) in RCA: 106] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Revised: 03/16/2013] [Accepted: 03/19/2013] [Indexed: 11/08/2022]
Abstract
Viruses influence oceanic ecosystems by causing mortality of microorganisms, altering nutrient and organic matter flux via lysis and auxiliary metabolic gene expression and changing the trajectory of microbial evolution through horizontal gene transfer. Limited host range and differing genetic potential of individual virus types mean that investigations into the types of viruses that exist in the ocean and their spatial distribution throughout the world's oceans are critical to understanding the global impacts of marine viruses. Here we evaluate viral morphological characteristics (morphotype, capsid diameter and tail length) using a quantitative transmission electron microscopy (qTEM) method across six of the world's oceans and seas sampled through the Tara Oceans Expedition. Extensive experimental validation of the qTEM method shows that neither sample preservation nor preparation significantly alters natural viral morphological characteristics. The global sampling analysis demonstrated that morphological characteristics did not vary consistently with depth (surface versus deep chlorophyll maximum waters) or oceanic region. Instead, temperature, salinity and oxygen concentration, but not chlorophyll a concentration, were more explanatory in evaluating differences in viral assemblage morphological characteristics. Surprisingly, given that the majority of cultivated bacterial viruses are tailed, non-tailed viruses appear to numerically dominate the upper oceans as they comprised 51-92% of the viral particles observed. Together, these results document global marine viral morphological characteristics, show that their minimal variability is more explained by environmental conditions than geography and suggest that non-tailed viruses might represent the most ecologically important targets for future research.
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Maurice CF, Bouvier C, de Wit R, Bouvier T. Linking the lytic and lysogenic bacteriophage cycles to environmental conditions, host physiology and their variability in coastal lagoons. Environ Microbiol 2013; 15:2463-75. [PMID: 23581698 DOI: 10.1111/1462-2920.12120] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Accepted: 03/05/2013] [Indexed: 01/21/2023]
Abstract
Changes in environmental conditions and prokaryote physiology can strongly affect the dynamics of both the lysogenic and lytic bacteriophage replication cycles in aquatic systems. However, it remains unclear whether it is the nature, amplitude or frequency of these changes that alter the phage replication cycles. We performed an annual survey of three Mediterranean lagoons with contrasting levels of chlorophyll a concentration and salinity to explore how these cues and their variability influence either replication cycle. The lytic cycle was always detected and showed seasonal patterns, whereas the lysogenic cycle was often undetected and highly variable. The lytic cycle was influenced by environmental and prokaryotic physiological cues, increasing with concentrations of dissolved organic carbon, chlorophyll a, and the proportion of respiring cells, and decreasing with the proportion of damaged cells. In contrast, lysogeny was not explained by the magnitude of any environmental or physiological parameter, but increased with the amplitude of change in prokaryote physiology. Our study suggests that both cycles are regulated by distinct factors: the lytic cycle is dependent on environmental parameters and host physiology, while lysogeny is dependent on the variability of prokaryote physiology. This could lead to the contrasting patterns observed between both cycles in aquatic systems.
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Affiliation(s)
- C F Maurice
- Université de Montpellier 2, Laboratoire Ecologie des Systèmes Marins Côtiers ECOSYM UMR5119 CNRS-Ifremer-IRD, case 093. Place Eugène Bataillon, 34095, Montpellier cedex 5, France
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14
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Kalinowska K, Guśpiel A, Kiersztyn B, Chróst RJ. Factors controlling bacteria and protists in selected Mazurian eutrophic lakes (North-Eastern Poland) during spring. AQUATIC BIOSYSTEMS 2013; 9:9. [PMID: 23566491 PMCID: PMC3626790 DOI: 10.1186/2046-9063-9-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/02/2013] [Accepted: 03/28/2013] [Indexed: 06/02/2023]
Abstract
BACKGROUND The bottom-up (food resources) and top-down (grazing pressure) controls, with other environmental parameters (water temperature, pH) are the main factors regulating the abundance and structure of microbial communities in aquatic ecosystems. It is still not definitively decided which of the two control mechanisms is more important. The significance of bottom-up versus top-down controls may alter with lake productivity and season. In oligo- and/or mesotrophic environments, the bottom-up control is mostly important in regulating bacterial abundances, while in eutrophic systems, the top-down control may be more significant. RESULTS The abundance of bacteria, heterotrophic (HNF) and autotrophic (ANF) nanoflagellates and ciliates, as well as bacterial production (BP) and metabolically active cells of bacteria (CTC, NuCC, EST) were studied in eutrophic lakes (Mazurian Lake District, Poland) during spring. The studied lakes were characterized by high nanoflagellate (mean 17.36 ± 8.57 × 103 cells ml-1) and ciliate abundances (mean 59.9 ± 22.4 ind. ml-1) that were higher in the euphotic zone than in the bottom waters, with relatively low bacterial densities (4.76 ± 2.08 × 106 cells ml-1) that were lower in the euphotic zone compared to the profundal zone. Oligotrichida (Rimostrombidium spp.), Prostomatida (Urotricha spp.) and Scuticociliatida (Histiobalantium bodamicum) dominated in the euphotic zone, whereas oligotrichs Tintinnidium sp. and prostomatids Urotricha spp. were most numerous in the bottom waters. Among the staining methods used to examine bacterial cellular metabolic activity, the lowest percentage of active cells was recorded with the CTC (1.5-15.4%) and EST (2.7-14.2%) assay in contrast to the NuCC (28.8-97.3%) method. CONCLUSIONS In the euphotic zone, the bottom-up factors (TP and DOC concentrations) played a more important role than top-down control (grazing by protists) in regulating bacterial numbers and activity. None of the single analyzed factors controlled bacterial abundance in the bottom waters. The results of this study suggest that both control mechanisms, bottom-up and top-down, simultaneously regulated bacterial community and their activity in the profundal zone of the studied lakes during spring. In both lake water layers, food availability (algae, nanoflagellates) was probably the major factor determining ciliate abundance and their composition. In the bottom waters, both groups of protists appeared to be also influenced by oxygen, temperature, and total phosphorus.
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Affiliation(s)
- Krystyna Kalinowska
- Polish Academy of Sciences, Centre for Ecological Research, Hydrobiological Station, ul. Leśna 13, Mikołajki, 11-730, Poland
| | - Adam Guśpiel
- Department of Microbial Ecology, Institute of Botany, Faculty of Biology, University of Warsaw, ul. Miecznikowa 1, Warsaw, 02-096, Poland
| | - Bartosz Kiersztyn
- Department of Microbial Ecology, Institute of Botany, Faculty of Biology, University of Warsaw, ul. Miecznikowa 1, Warsaw, 02-096, Poland
| | - Ryszard J Chróst
- Department of Microbial Ecology, Institute of Botany, Faculty of Biology, University of Warsaw, ul. Miecznikowa 1, Warsaw, 02-096, Poland
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15
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Colombet J, Sime-Ngando T. Seasonal depth-related gradients in virioplankton: lytic activity and comparison with protistan grazing potential in Lake Pavin (France). MICROBIAL ECOLOGY 2012; 64:67-78. [PMID: 22391799 DOI: 10.1007/s00248-012-0032-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2011] [Accepted: 02/17/2012] [Indexed: 05/31/2023]
Abstract
This study presents an original depth-related survey of virioplankton lytic activity in relation to prokaryotic production and potential protistan bacterivory in the deep (Z(max) = 92 m) meromictic volcanic Lake Pavin (Massif Central, France). The sampling strategy was designed to be representative of the physico-chemical gradients of the water column of the lake, and of the seasonal variability as well, i.e. 12 different depths sampled in triplicates from April to December 2005. In the space, viral lytic activity estimated from the frequency of visibly infected prokaryotic cells and from burst size over the study period generally decreased with depth. This was viewed as a paradox compared to the abundances of viruses and prokaryotes and to the prokaryotic production which increased with depth. The seasonal variability in viral lytic activity was correlated with prokaryotic variables (abundance and production) in the deepest waters, i.e. from the hypolimnion downwards. Compared to previous studies known from the mixolimnion, we conclude that the deep waters in Lake Pavin represent an exclusive environment for heterotrophic prokaryotes whose seasonal activity offers an optimal and unique resource for thriving viral communities, some of which may be typical, endemic to the ambient dark, cold and stable deep water masses. Overall, the main findings in the present study get well around a previous statement that the ecology of the deepest waters of Lake Pavin is essentially driven by the dark viral loop (dissolved organic matter-prokaryotes-viruses) processes, which can sequester organic matters and nutrients for a long-lived turnover time. This is in agreement with recent demonstrations from marine systems that meso- and bathypelagic waters are optimal environments for viral survival and proliferation.
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Affiliation(s)
- Jonathan Colombet
- Laboratoire Microorganismes: Génome et Environnement, Clermont Université Blaise Pascal, UMR CNRS 6023, Aubière, France
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16
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High lytic infection rates but low abundances of prokaryote viruses in a humic lake (Vassivière, Massif Central, France). Appl Environ Microbiol 2011; 77:5610-8. [PMID: 21724889 DOI: 10.1128/aem.01370-10] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We explored the abundance and infection rates of viruses on a time series scale in the euphotic zone of the humic mesotrophic Lake Vassivière (Massif Central, France) and compared them to nonhumic lakes of contrasting trophy (i.e., the oligomesotrophic Lake Pavin and the eutrophic Lake Aydat) located in the same geographical region and sampled during the same period. In Lake Vassivière, the abundances of virus-like particles (range, 1.7 × 10(10) to 2.6 × 10(10) liter(-1)) were significantly (P < 0.001) lower than in Lakes Pavin and Aydat. The percentage of virus-infected prokaryotic cells (mean, 18.0%) was significantly higher (P < 0.001) in Vassivière than in Pavin (mean, 11.5%) and Aydat (mean, 9.7%). In Vassivière, the abundance of prokaryotes was a good predictor (r = 0.78, P < 0.001) of the number of virus-like particles, while the potential grazing rate from heterotrophic nanoflagellates was positively correlated to the viral infection rate (r = 0.75, P < 0.001; n = 20), indicating the prevalence of cycling interactions among viruses, prokaryotes, and grazers, which is in agreement with past experiments. The absence of correlation between chlorophyll a concentrations (Chl) and viral parameters suggested that the resources for the lytic activity of viruses in Vassivière were mainly under allochthonous control, through host activity. Indeed, compilation of data obtained from several nonhumic lakes in the French Massif Central revealed that Chl was positively correlated to the abundance of virus-like particles at concentrations above 0.5 μg Chl liter(-1) and negatively at concentrations below 0.5 μg Chl liter(-1), suggesting that phytoplankton-derived resources could force prokaryotic growth to attain a certain threshold level when the host availability is sufficient to boost the proliferation of viruses. Therefore, based on the high level of lytic infection rates in Lake Vassivière, we conclude that viruses are key agents for prokaryotic mortality and could influence the food web dynamics in humic lakes, which may ultimately depend on the internal cycling of resources and, perhaps, mainly on the allochthonous inputs and the associated humic substances.
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17
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Bouvy M, Bettarel Y, Bouvier C, Domaizon I, Jacquet S, Le Floc'h E, Montanié H, Mostajir B, Sime-Ngando T, Torréton JP, Vidussi F, Bouvier T. Trophic interactions between viruses, bacteria and nanoflagellates under various nutrient conditions and simulated climate change. Environ Microbiol 2011; 13:1842-57. [DOI: 10.1111/j.1462-2920.2011.02498.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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18
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Bottom-up versus top-down control of hypo- and epilimnion free-living bacterial community structures in two neighboring freshwater lakes. Appl Environ Microbiol 2011; 77:3591-9. [PMID: 21478309 DOI: 10.1128/aem.02739-10] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bacterioplankton plays a central role in the microbial functioning of lacustrine ecosystems; however, factors that constrain its structural variation are still poorly understood. Here we evaluated the driving forces exerted by a large set of environmental and biological parameters on the temporal and spatial dynamics of free-living bacterial community structures (BCS) in two neighboring perialpine lakes, Lake Bourget and Lake Annecy, which differ in trophic status. We analyzed monthly data from a 1-year sampling period at two depths situated in the epi- and hypolimnia for each lake. Overall, denaturing gradient gel electrophoresis (DGGE) revealed significant differences in the BCS in the two lakes, characterized by a higher number of bands in the oligotrophic ecosystem (i.e., Lake Annecy). The temporal dynamics of BCS differed greatly between depths and lakes, with temporal scale patterns being much longer in the mesotrophic Lake Bourget. Direct-gradient multivariate ordination analyses showed that a complex array of biogeochemical parameters was the driving force behind BCS shifts in both lakes. Our results indicated that 60 to 80% of the variance was explained only by the bottom-up factors in both lakes, indicating the importance of nutrients and organic matter from autotrophic origin in controlling the BCS. Top-down regulation by flagellates together with ciliates or viruses was found only in the hypolimnion and not in the epilimnion for both lakes and explained less than 18% of the bacterial community changes during the year. Our study suggests that the temporal dynamics of the free-living bacterial community structure in deep perialpine lakes are dependent mainly on bottom-up factors and to a lesser extent on top-down factors, whatever the specific environmental conditions of these lakes.
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Brum JR, Steward GF. Morphological characterization of viruses in the stratified water column of alkaline, hypersaline Mono Lake. MICROBIAL ECOLOGY 2010; 60:636-43. [PMID: 20521038 DOI: 10.1007/s00248-010-9688-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2009] [Accepted: 05/06/2010] [Indexed: 05/25/2023]
Abstract
Concentrations of viruses and prokaryotes in the alkaline, moderately hypersaline, seasonally stratified Mono Lake are among the highest reported for a natural aquatic environment. We used electron microscopy to test whether viral morphological characteristics differed among the epilimnion, metalimnion, and the anoxic hypolimnion of the lake and to determine how the properties of viruses in Mono Lake compare to other aquatic environments. Viral capsid size distributions were more similar in the metalimnion and hypolimnion of Mono Lake, while viral tail lengths were more similar in the epilimnion and metalimnion. The percentage of tailed viruses decreased with depth and the relative percentages of tailed phage families changed with depth. The presence of large (>125 nm capsid), untailed viruses in the metalimnion and hypolimnion suggests that eukaryotic viruses are produced in these suboxic and anoxic, hypersaline environments. Capsid diameters of viruses were larger on average in Mono Lake compared to other aquatic environments, and no lemon-shaped or filamentous viruses were found, in contrast to other high-salinity or high-altitude lakes and seas. Our data suggest that the physically and chemically distinct layers of Mono Lake harbor different viral assemblages, and that these assemblages are distinct from other aquatic environments that have been studied. Furthermore, we found that filtration of a sample through a 0.22-µm pore-size filter significantly altered the distribution of viral capsid diameters and tail lengths, resulting in a relative depletion of viruses having larger capsids and longer tails. This observation highlights the potential for bias in molecular surveys of viral diversity, which typically rely on filtration through 0.2- or 0.22-µm pore-size membrane filters to remove bacteria during sample preparation.
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Affiliation(s)
- Jennifer R Brum
- Department of Oceanography, University of Hawai'i at Manoa, 1000 Pope Rd., MSB 205, Honolulu, HI 96822, USA.
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20
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Indirect interactions in the microbial world: specificities and similarities to plant–insect systems. POPUL ECOL 2010. [DOI: 10.1007/s10144-010-0235-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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21
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Lepère C, Masquelier S, Mangot JF, Debroas D, Domaizon I. Vertical structure of small eukaryotes in three lakes that differ by their trophic status: a quantitative approach. ISME JOURNAL 2010; 4:1509-19. [DOI: 10.1038/ismej.2010.83] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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22
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Colombet J, Charpin M, Robin A, Portelli C, Amblard C, Cauchie HM, Sime-Ngando T. Seasonal depth-related gradients in virioplankton: standing stock and relationships with microbial communities in Lake Pavin (France). MICROBIAL ECOLOGY 2009; 58:728-736. [PMID: 19475444 DOI: 10.1007/s00248-009-9535-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2008] [Accepted: 05/06/2009] [Indexed: 05/27/2023]
Abstract
This study presents a depth-related survey of virioplankton abundance in Lake Pavin (Massif Central, France), in relation to the abundances of heterotrophic prokaryotes, picocyanobacteria (Pcy), autotrophic picoeukaryotes (Peu), and of autotrophic (ANF) and heterotrophic (HNF) nanoflagellates. The sampling strategy was designed to be representative of the physico-chemical gradients of the whole water column of the lake, and the seasonal variability as well. In mixolimnic surface waters, all communities were present and viral abundance peaked in summer and autumn. Viral abundance was significantly correlated (p < 0.001) with Pcy, Peu, and ANF, indicating that cyanophages and perhaps other phytoplankton viruses represent a significant pool of viral standing stocks in the mixolimnion of Lake Pavin. Microautotrophs were absent in the deep monimolimnic water masses, where viruses and heterotrophic prokaryotes exhibited highest seasonal abundances in summer and/or autumn and were significantly correlated (p < 0.001) to each other. This indicates that the anoxic monimolimnion of Lake Pavin is an exclusive habitat for viruses and heterotrophic prokaryotes. We conclude that in this habitat, host availability is prevalent over other factors (temperature, oxygen, nutrients, grazers) in favoring viral proliferation.
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Affiliation(s)
- J Colombet
- LMGE, Laboratoire Microorganismes Génome & Environnement, UMR CNRS 6023, Université Blaise Pascal (Clermont-Ferrand II), 63177, Aubière Cedex, France
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Pradeep Ram AS, Sime-Ngando T. Resources drive trade-off between viral lifestyles in the plankton: evidence from freshwater microbial microcosms. Environ Microbiol 2009; 12:467-79. [PMID: 19878265 DOI: 10.1111/j.1462-2920.2009.02088.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Viruses have evolved different life strategies for coping with environmental challenges and this is a key explanation for their omnipresence in aquatic systems. However, factors that determine the balance between lytic versus lysogenic decision within natural virioplankton are poorly documented, primarily in freshwaters. This study was designed to investigate the experimental short-term (24 h incubation) effects of added organic and inorganic nutrients on the two viral lifestyles in nutrient-depleted freshwater microbial (i.e. <0.8 microm fraction) microcosms, using mitomycin C as prophage inductor agent. In the absence of mitomycin, viral lytic production increased as a functional response to the strong stimulation of bacterial growth rates (0.7-0.8 day(-1)) by the added nutrients, primarily the organic nutrients which appeared scarcer than inorganic nutrients and was related to the sampling period and the geomorphological peculiarities of Lake Pavin. In the presence of mitomycin, temperate phage production (frequency of lysogenically infected bacterial cells, FLC=17-19% of total cells) significantly exceeded lytic production (frequency of lytically infected bacterial cells, FIC=9-11%) in natural samples (i.e. without nutrient additions) as a result of enhanced prophage induction, which relatively increased with the decreasing contact probability between viruses and their potential hosts. In contrast, addition of nutrients drastically reduced FLC (<4%) and increased FIC (>22%). Both variables were antagonistically correlated as was the correlation between FLC and bacterial growth rates, supporting the idea that lysogeny may represent a maintenance strategy for viruses in harsh nutrient/host conditions which appeared as major instigators of the trade-off between the two viral lifestyles. Overall, at the community level, we reject the hypothesis that nutrients but mitomicyn C stimulate temperate phage induction, and retained the hypotheses that nutrients rather (i) stimulate lytic viruses via enhanced host growth and (ii) when limiting, promote lysogenic conversion in natural waters.
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Affiliation(s)
- A S Pradeep Ram
- Laboratoire Microorganismes: Génome et Environnement, UMR CNRS 6023, Université Blaise Pascal, Clermont-Ferrand II, 63177 Aubière Cedex, France
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Abstract
In this review, available data on the structure (diversity, abundance, biomass) and functional imprints (bacteriolysis, lysogeny, gene transfers, regulation of prokaryotic diversity) of natural viruses in the context of food webs in aquatic microbial ecology, and the related biogeochemical cycles, are summarized. Viruses are the most abundant, and probably the most diverse, biological entities in aquatic ecosystems and in the biosphere (i.e., viriosphere). Aquatic viruses typically exceed 107 particles/mL in mesotrophic conditions, the majority being represented by phages without tails and by tailed-phages such as members of the family Siphoviridae. Both types of phages have a small capsid and a small genome size, which is considered an evolutionary adaptation to planktonic life. Their contribution to microbial mortality is significant. There is strong evidence that phages exert a significant pressure on the community structure and diversity and on the diversification of potential hosts, mainly through two major pathways: biogeochemical catalysis from lysis products and horizontal gene transfers. In turn, phages are sensitive to environmental factors, both in terms of integrity and of infectivity. Some phages contain typical viral genes that code for biological functions of interest, such as photosynthesis. In general, development in viral ecology is a source of new knowledge for the scientific community in the domain of environmental sciences, but also in the context of evolutionary biology of living cellular organisms, the obligatory hosts for viruses. For example, the recent discovery of a giant virus that becomes ill through infection by another virus (i.e., a viriophage) is fuelling debate about whether viruses are alive. Finally, future research directions are identified in the context of general aquatic ecology, including ecological researches on cyanophages and other phytoplanktonic phages as a priority, primarily in freshwater lakes.
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Short-term variations in abundances and potential activities of viruses, bacteria and nanoprotists in Lake Bourget. Ecol Res 2007. [DOI: 10.1007/s11284-007-0448-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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26
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Lefèvre E, Bardot C, Noël C, Carrias JF, Viscogliosi E, Amblard C, Sime-Ngando T. Unveiling fungal zooflagellates as members of freshwater picoeukaryotes: evidence from a molecular diversity study in a deep meromictic lake. Environ Microbiol 2007; 9:61-71. [PMID: 17227412 DOI: 10.1111/j.1462-2920.2006.01111.x] [Citation(s) in RCA: 182] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
This study presents an original 18S rRNA PCR survey of the freshwater picoeukaryote community, and was designed to detect unidentified heterotrophic picoflagellates (size range 0.6-5 microm) which are prevalent throughout the year within the heterotrophic flagellate assemblage in Lake Pavin. Four clone libraries were constructed from samples collected in two contrasting zones in the lake. Computerized statistic tools have suggested that sequence retrieval was representative of the in situ picoplankton diversity. The two sampling zones exhibited similar diversity patterns but shared only about 5% of the operational taxonomic units (OTUs). Phylogenetic analysis clustered our sequences into three taxonomic groups: Alveolates (30% of OTUs), Fungi (23%) and Cercozoa (19%). Fungi thus substantially contributed to the detected diversity, as was additionally supported by direct microscopic observations of fungal zoospores and sporangia. A large fraction of the sequences belonged to parasites, including Alveolate sequences affiliated to the genus Perkinsus known as zooparasites, and chytrids that include host-specific parasitic fungi of various freshwater phytoplankton species, primarily diatoms. Phylogenetic analysis revealed five novel clades that probably include typical freshwater environmental sequences. Overall, from the unsuspected fungal diversity unveiled, we think that fungal zooflagellates have been misidentified as phagotrophic nanoflagellates in previous studies. This is in agreement with a recent experimental demonstration that zoospore-producing fungi and parasitic activity may play an important role in aquatic food webs.
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Affiliation(s)
- Emilie Lefèvre
- Laboratoire de Biologie des Protistes, UMR CNRS 6023, Université Blaise Pascal (Clermont-Ferrand II), F-63177, Aubière Cedex, France
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