Effect%20of%20viruses%20on%20bacteria-mediated%20C%20and%20Fe%20cycling

1
Effect of viruses on bacteria-mediated C and Fe
cycling

• M.G. Weinbauer
• CNRS-UPMC, UMR 7093
• Villefranche-sur-mer

2
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
5000ml
2(-3)
Viral diversity
4-5 (total)
100-200L
Viral and bacterial metagenomics
5
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

100 kDa
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