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Effect of viruses on bacteria-mediated C and Fe cycling

Effect of viruses on bacteria-mediated C and Fe cycling. M.G. Weinbauer CNRS-UPMC, UMR 7093 Villefranche-sur-mer. Inorganic. Nutrients. Dissolved. Organic. Matter. Microbial. loop. Heterotrophic. Prokaryotes. The ‘viral shunt’. Wilhelm and Suttle (1999). Grazing food chain.

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Effect of viruses on bacteria-mediated C and Fe cycling

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  1. Effect of viruses on bacteria-mediated C and Fe cycling M.G. Weinbauer CNRS-UPMC, UMR 7093 Villefranche-sur-mer

  2. Inorganic Nutrients Dissolved Organic Matter Microbial loop Heterotrophic Prokaryotes The ‘viral shunt’ Wilhelm and Suttle (1999) Grazing food chain Primary Producers Grazers Carnivores 100% 1% 2-10% Viruses 6-26% 3-15% Viral shunt Viral lysis influences biogeochemical cycles

  3. In situ samples Method Parameter Viral (and bacterial) abundance Flow cytomety Abundance of several viral (and bacterial) populations Flow cytomety Phage production Virus-dilution approach Frequency of lytically infected bacterial cells Virus-dilution approach Frequency of lysogenically infected bacterial cells Virus-dilution approach Pulsed-field gel electrophoresis DGGE? Viral diversity

  4. In situ samples No of samples per depth profile Volume per depth Parameter Viral (and bacterial) abundance Abundance of populations 4 ml 6 Phage production Frequency of lytically infected bacterial cells Frequency of lysogenically infected bacterial cells 2-300ml 3-4 2(-3) 5000ml Viral diversity 4-5 (total) 100-200L Viral and bacterial metagenomics

  5. 70 in out 60 50 FIC (%) 40 30 20 10 0 0 5 10 15 20 Time since first iron addition (days) Effect of viruses on bacteria-mediated Fe dissolution Background: Viral lysis increases bacterial respiration and decreases growth efficiency by setting free the cell content during lysis. Bacteria are rich in Fe. Fe fertilization stimulates viral infection of bacterioplankton Hypothesis: Lysis should increase the pool of dissolved Fe and the high growth efficiency should increase dissolution of organically complexed Fe. This should have consequences for the distribution of Fe in different pools and for fluxes between pools and thus for carbon cycling.

  6. Effect of viruses on bacteria-mediated Fe dissolution (continued) Factorial approach: Bacterial communities with and without viruses could be ammended with and without Fe. Bacterial production and respiration could be measured, Fe in the LMW DOM, HMW DOM and bacterial pool could be measured, maybe hot Fe additions could be used to quantify Fe fluxes between pools. Collaboration: Geraldine Sarthou, others? An extension could be to add viral lysis products to natural communities to see whether dissolution of complexed iron stimulates primary production. Samples for 16S PCR DGGE will reveal potential influences of these mechanisms for bacterial species richness.

  7. Factorial approach Water sample Bacterial concentrate 1-µm Viral concentrate 0.2-µm • Viruses • + Bacteria 100kDa + Viruses + Bacteria Virus-free water +Fe/-Fe

  8. Viral diversity Pulsed-field gel electrophoresis separates viral genomes by size Bands can be excised and further analyzed by PCR-DGGE for specific groups Primers are available for cyanophages algal viruses Podoviridae?

  9. Metagenomics (=Community genomics) Use of metagenomics: Diversity estimates for various groups (viruses, bacteria,…18S rRNA) 2. Functional display: Detection of gene expression that differs between Fe-limited and Fe-replete stations and is thus likely linked to induction by presence/absence of Fe. Collaboration with Dirk Wenderoth, German Centre for Biotechnology From the same samples collected for metagenomics, an analysis of stable isotope composition of total proteins and lipids and specific Compounds could be performed for carbon and nitrogen. This may help to tease apart the flow of carbon and nitrogen through communities in Fe-limited and Fe-repleted stations. Collaboration with Wolf-Rainer Abraham, German Centre for Biotechnology

  10. A virus-reduction approach to estimate viralproduction, frequency of infected cells and prophage induction Frequency of infected cells (FIC): (VACt1 - VAt0)/BS/BA VAMCt1 Frequency of lysogenic cells (FLC): (VAMCt1 - VACt1)/BS/BA Prophage induction Viral production-slope method (VP-Slope): Slope of regression of viral abundance over time Lytic viral production VACt1 VAt0 Viral production-FIC, BP, BS method: FICxBP (bacterial production) xBS Dyfamed (French JGOFS station) NW Mediterranean Sea Weinbauer & Suttle 1996, Wilhelm et al. 2002 Weinbauer et al. 2002

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