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

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

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

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

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. Hypothesis: Lysis should increase the pool of dissolved Fe and the high growth efficiency should increase dissolution of organically complexed Fe. Bacteria are rich in Fe in out FIC (%) Time since first iron addition (days) Fe fertilization stimulates viral infection of bacterioplankton This should have consequences for the distribution of Fe in different pools and for fluxes between pools and thus for carbon cycling.

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.

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

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?

Metagenomics (=Community genomics) Collaboration with Dirk Wenderoth, German Centre for Biotechnology Use of metagenomics: 1.Diversity estimates for various groups (viruses, bacteria,…18S rRNA) 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 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.

A virus-reduction approach to estimate viral production, frequency of infected cells and prophage induction Dyfamed (French JGOFS station) NW Mediterranean Sea Lytic viral production Prophage induction VA t0 VA MCt1 VA Ct1 Frequency of infected cells (FIC): ( VA Ct1 - VA t0 )/BS/BA Frequency of lysogenic cells (FLC): ( VA MCt1 - VA Ct1 )/BS/BA Viral production-slope method (VP-Slope): Slope of regression of viral abundance over time Viral production-FIC, BP, BS method: FICxBP (bacterial production) xBS Weinbauer & Suttle 1996, Wilhelm et al Weinbauer et al. 2002