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Transcript
Effect of viruses on bacteria-mediated C and
Fe cycling
M.G. Weinbauer
CNRS-UPMC, UMR 7093
Villefranche-sur-mer
The ‘viral shunt’
Wilhelm and Suttle (1999)
Grazing food chain
Primary Producers
100%
Inorganic
Nutrients
Carnivores
Grazers
1%
2-10%
Dissolved
Organic
Matter
6-26%
Viral shunt
Viruses
3-15%
Heterotrophic
Prokaryotes
Microbial
loop
Viral lysis influences biogeochemical cycles
In situ samples
Parameter
Method
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
Viral diversity
Pulsed-field gel electrophoresis
DGGE?
In situ samples
Parameter
No of samples Volume per depth
per depth profile
Viral (and bacterial) abundance
Abundance of populations
6
4 ml
Phage production
Frequency of lytically infected
bacterial cells
Frequency of lysogenically
infected bacterial cells
3-4
2-300ml
Viral diversity
2(-3)
5000ml
Viral and bacterial
metagenomics
4-5
(total)
100-200L
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.
70
in
out
Fe fertilization stimulates viral
infection of bacterioplankton
FIC (%)
60
50
40
30
20
10
Hypothesis:
0
0
5
10
15
20
Time since first iron addition (days)
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.
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.
Factorial
approach
Water sample
Bacterial
concentrate
1-µm
Viral
concentrate
0.2-µm
-Viruses
+ Bacteria
100 kDa
Virus-free
water
+ Viruses
+ Bacteria
+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?
Q uic kTim e™ et un décom pr esseur TI FF ( non com pr essé) sont r equis pour vis ionner cet t e im age.
Metagenomics (=Community genomics)
Use of metagenomics:
1. 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
Viral abundance (106 ml-1)
A virus-reduction approach to estimate viral
production, frequency of infected cells and prophage induction
0,8
y = 0,018x + 0,210
VAMCt1
Prophage
induction
0,6
0,4
0,2
0
Frequency of infected cells (FIC):
(VACt1 - VAt0)/BS/BA
VACt1
VAt0
0
Mitomycin C
Control
5
10
15
20
Lytic viral
production
Frequency of lysogenic cells (FLC):
(VAMCt1 - VACt1)/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
Time (h)
Dyfamed (French JGOFS station)
NW Mediterranean Sea
Weinbauer & Suttle 1996, Wilhelm et al. 2002
Weinbauer et al. 2002