effect of viruses on bacteria-mediated c and fe cycling m.g. weinbauer cnrs-upmc, umr 7093...
TRANSCRIPT
Effect of viruses on bacteria-mediated C and Fe cycling
M.G. Weinbauer
CNRS-UPMC, UMR 7093
Villefranche-sur-mer
HeterotrophicProkaryotes
DissolvedOrganicMatter
Primary Producers Grazers Carnivores
VirusesInorganicNutrients
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 (andbacterial) populations
Flow cytomety
Phage production
Frequency of lytically infectedbacterial cells
Frequency of lysogenicallyinfected bacterial cells
Virus-dilution approach
Virus-dilution approach
Virus-dilution approach
MethodParameter
Viral diversityPulsed-field gel electrophoresisDGGE?
In situ samples
Viral (and bacterial) abundanceAbundance of populations 6 4 ml
Phage productionFrequency of lytically infectedbacterial cellsFrequency of lysogenicallyinfected bacterial cells
2-300ml3-4
No of samples per depth profile
Parameter
Viral diversity 5000ml
Volume per depth
2(-3)
Viral and bacterialmetagenomics
100-200L
4-5 (total)
Effect of viruses on bacteria-mediated Fe dissolution
Background:
Viral lysis increases bacterial respiration and decreases growth efficiencyby 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.
0
10
20
30
40
50
60
70
0 5 10 15 20
inout
FIC
(%
)
Time since first iron addition (days)
Fe fertilization stimulates viralinfection of bacterioplankton
This should have consequences for the distribution of Fe in different poolsand 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
Bacterialconcentrate
-Viruses+ Bacteria
Viral concentrate
+ Viruses+ Bacteria
Factorialapproach
+Fe/-Fe
QuickTime™ et un décompresseur TIFF (non compressé) sont requis pour visionner cette image.
Viral diversity
Pulsed-field gel electrophoresisseparates viral genomes by size
Bands can be excised and furtheranalyzed by PCR-DGGE for specific groups
Primers are available for cyanophagesalgal virusesPodoviridae?
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 ofstable isotope composition of total proteins and lipids and specific Compounds could be performed for carbon and nitrogen. This may helpto tease apart the flow of carbon and nitrogen through communities inFe-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 viralproduction, frequency of infected cells and prophage
induction
Dyfamed (French JGOFS station)NW Mediterranean Sea
0
0,2
0,4
0,6
0,8
Vir
al ab
un
dan
ce (
10
6 m
l-1)
0 5 10 15 20
Time (h)
y = 0,018x + 0,210
Control
Mitomycin C
Lytic viral production
Prophage induction
VAt0
VAMCt1
VACt1
Frequency of infected cells (FIC):(VACt1 - VAt0)/BS/BA
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, BSmethod: FICxBP (bacterial production)xBS
Weinbauer & Suttle 1996, Wilhelm et al. 2002Weinbauer et al. 2002