First estimates of viral impact on bacterial communities in large French alpine lakes Personnic Sébastien S 1 Domaizon Isabelle 2 & Jacquet Stéphan 1 (1) INRA - CARRTEL, Group of Aquatic Microbial Ecology (GAME), Thonon les Bains, France (2) Université de Savoie - CARRTEL, Group of Aquatic Microbial Ecology (GAME), Le Bourget du Lac, France
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Localization, Characteristics Switzerland Aubonne Morges Venoge Lausanne Nyon 0 2 Thonon 0 Evian 0 2 Veveyse 1 Dranse Rhône Lac supérieure Rhône Genève Lac inférieure 0 5 km France Lake Geneva Altitude 372 m Width 14 km Length 72 km Max. Depth 9 m Area 585 km 2 Volume 86 x 9 m 3 Catchments Area 7,395 km 2 Trophic status Mesotrophic
Localization, Characteristics Lake Bourget Altitude 232 m Width 3.5 km Length 18 km Max. Depth 147 m Area 44.62 km 2 Volume 3.6 x 9 m 3 Trophic status Mesotrophic
Localization, Characteristics Lake Annecy Altitude 447 m Width 3,2 km Length 14,6 km Max. Depth 65 m Area 28 km 2 Volume 1.1 x 9 m 3 Trophic status Oligotrophic
Dynamics of microbial communities Lake Geneva Depth (m) PE rich synechococcus spp. (cells.ml -1 ) 0 2e+4 4e+4 6e+4 8e+4 1e+5 8 depths between 0- meters 2 samples per month Physical, chemical, ciliates flagellates data not shown Flow cytometry counts Depth (m) Depth (m) Depth (m) Small Eukaryotes (cells.ml -1 ) Het. Bacteria (cells.ml -1 ) Viruses (part.ml -1 ) 00 000 0 000 0 000 0 1e+6 2e+6 3e+6 4e+6 5e+6 6e+6 7e+6 8e+6 9e+6 Nov May Nov May Nov May Nov 03 04 05 5e+7 1e+8 2e+8 2e+8
Dynamics of microbial communities Lake Bourget Depth (m) PE rich synechococcus spp. (cells.ml -1 ) 0 2e+4 4e+4 6e+4 8e+4 1e+5 7 depths between 0- meters 2 samples per month Physical, chemical, ciliates flagellates data not shown Depth (m) Depth (m) Depth (m) Small Eukaryotes (cells.ml -1 ) Het. Bacteria (cells.ml -1 ) Viruses (part.ml -1 ) 00 000 0 000 0 000 1e+6 2e+6 3e+6 4e+6 5e+6 6e+6 7e+6 8e+6 9e+6 Nov May Nov May Nov May Nov 03 04 05 5e+7 1e+8 2e+8 2e+8
Dynamics of microbial communities Lake Annecy Depth (m) PE rich synechococcus spp. (cells.ml -1 ) 0 2e+4 4e+4 6e+4 8e+4 1e+5 7 depths between 0- meters 2 samples per month Physical, chemical, ciliates flagellates data not shown Depth (m) Depth (m) Depth (m) Small Eukaryotes (cells.ml -1 ) Het. Bacteria (cells.ml -1 ) 00 000 0 000 0 1e+6 2e+6 3e+6 4e+6 5e+6 5e+7 1e+8 2e+8 Viruses (part.ml -1 ) 2e+8 Nov May Nov May Nov May Nov 03 04 05
relationships between microbial communities and environmental parameters ANNECY Lake BOURGET Lake 1,0 1,0 Factor 2 : 23,18% 0,5 0,0-0,5 Si NO3 VLP1 T c TOC VLP2 NH4 HB PCPO4 Factor 2 : 14,89% 0,5 0,0-0,5 Si PO4 NO3 Chla AEP PC * VLP1 * VLP2 HB T c TOC Exploratory analysis using PCA AEP Chla NH4-1,0-1,0-1,0-0,5 0,0 0,5 1,0 Factor 1 :,80% ANNECY Lake 4-1,0-0,5 0,0 0,5 1,0 Factor BOURGET 1 : 48,95% Lake 4 2 Hypolimnion all dates Epilimnion June Epilimnion Oct -Nov 3 2 1 Hypolimnion all dates Epilimnion end Oct- Nov Epilimnion Jul-Sept- early Oct Factor 2: 23,18% 0-2 -4-6 Epi - Meta- lmlinion March April May Epilmlinion May Factor 2: 14,06% 0-1 -2-3 -4 May Epilimnion April - May -5-4 -3-2 -1 0 1 2 3 4 5 Factor 1:,80% -5-4 -2 0 2 4 6 Factor 1: 48,17%
4 groups of VLPs Flow cytometry analysis Heterotrophic BACTERIA VLP2 VLP1 VLP3 Viruses VLP4 DNA Dye Complex Fluorescence Side Scatter
Co evolution between VLPs and possible hosts Cells. ml -1 Depth (m) Heterotrophic Bacteria 1e+6 2e+6 3e+6 4e+6 5e+6 6e+6 7e+6 Depth (m) VLP1 r= 0.48 p= 0.03 n= 21 Mar May Jul Sep Nov Part. ml -1 2.0e+7 4.0e+7 6.0e+7 8.0e+7 1.0e+8 1.2e+8 Date
Co evolution between VLPs and possible hosts Pico nano Cyanobacteria Cells. ml -1 0 2e+4 4e+4 6e+4 8e+4 1e+5 VLP2 r= 0.49 P<0.01 n= 60 Mar May Jul Sep Nov Part. ml -1 2e+6 4e+6 6e+6 8e+6 1e+7
Co evolution between VLPs and possible hosts Small Eukaryotes r= 0.88 P<0.01 n= 32 VLP 4 r= 0.57 P<0.01 Mar May Jul Sep Nov Cells. ml -1 0 00 00 6000 8000 000 n= 28 Part. ml -1 2.0e+5 4.0e+5 6.0e+5 8.0e+5 1.0e+6 1.2e+6 Identification of VLP - Viruses diversity : Coming soon
Impact of viruses and protozoan predators on bacterial mortality (experimental approach) Dilution Technique Inspired by Evans et al. (03) Modified by Jacquet et al. (05) Water filtered on 11-µm pore size Bacteria Net Growth rate Diluant free viruses and predators (water filtered on 0,02 µm) Diluant free predators (water filtered on 0,2 µm) 0 60 80 0 Dilution Contacts bacteria/viruses
Lake Geneva 05 Spring Viruses (part.ml -1 ) Jan May Sep Heterotrophic Bacteria Mortality EXP. Lake Geneva March 06 EXP. Lake Bourget April 06 EXP. Lake Annecy April 06 EXP. Lake Geneva May 06 EXP. Lake Geneva May 04 Viral lyses 2,3 %.d -1,4 %.d -1 9.5 %.d -1,4 %.d -1 3,8 %.d -1 2.0e+7 4.0e+7 6.0e+7 8.0e+7 1.0e+8 1.2e+8 1.4e+8 1.6e+8 Flagellates Grazing 0,4 %.d -1 8,7 %.d -1 32 %.d -1 Up to % of bacterial mortality can be explained by viral lysis Mortality due to viral lysis occasionally overpass mortality due to flagellates grazing
Lake Geneva 05 Viruses (part.ml -1 ) Jan May Sep 2.0e+7 4.0e+7 6.0e+7 8.0e+7 1.0e+8 1.2e+8 1.4e+8 1.6e+8 Heterotrophic Bacteria Mortality Viral lyses Flagellates Grazing Autumn EXP. Lake Geneva October 05 EXP. Lake Bourget October 05 EXP. Lake Annecy October 05 0 %.d -1 28 %.d -1 14%.d -1 0 %.d -1 No predators and viruses impact in Lake Annecy in the last weeks of October
Lake Geneva 05 Viruses (part.ml -1 ) Jan May Sep 2.0e+7 4.0e+7 6.0e+7 8.0e+7 1.0e+8 1.2e+8 1.4e+8 1.6e+8 Heterotrophic Bacteria Mortality Viral lyses Flagellates Grazing Winter EXP. Lake Geneva January 06 EXP. Lake Bourget January 06 EXP. Lake Annecy January 06 0 %.d -1 0 %.d -1 0 %.d -1 0 %.d -1 0 %.d -1 0 %.d -1 No impact of viruses and flagellates in winter? Dilution techniques not applicable at that time of the year? Dilution performed may be too strong in winter (small number of biological entities! decrease in frequency of viruses-host contacts) No Predator and virus impact in winter on bacterial net growth.(strong regulation by temperature, DOC or other chemical parameters?)
Conclusions A Small Inter annual variability in dynamics of microbial communities (cyanobacteria,, heterotrophic bacteria, VLP) with seasonal succession repeated from one year to another Maximum of viruses in October suggesting a viral termination of bacterial blooms in autumn?. Nevertheless in periods of high viral abundance we did not observe any correlation between the number of viruses and virus induced bacterial mortality. No correlation between VBR and viruses impacts Large seasonal variability of viruses and predators impact on heterotrophic bacteria mortality. No impact of viruses in winter? How do they persist in the water column (Lysogeny( Lysogeny,, Chronic infection ) )? What are the indirect effects of viral lysis on DOC?
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Lake Geneva 05 Spring Viruses (part.ml -1 ) Jan May Sep Heterotrophic Bacteria Mortality EXP. Lake Geneva March 06 EXP. Lake Bourget April 06 EXP. Lake Annecy April 06 EXP. Lake Geneva May 06 EXP. Lake Geneva May 04 Viral lyses 2,3 %.d -1,4 %.d -1 9.5 %.d -1,4 %.d -1 3,8 %.d -1 2.0e+7 4.0e+7 6.0e+7 8.0e+7 1.0e+8 1.2e+8 1.4e+8 1.6e+8 Flagellates Grazing 0,4 %.d -1 8,7 %.d -1 32 %.d -1 Negative impact of viruses in the mortality of bacteria? Or just a dilution techniques aberration? If it s a negative impact at this period: Maybee viruses favor bacteria growth? (variation in the quality of DOC due to cell lyses?) or predators favors viral lyses? (variation in cell composition or cell receptors) Jacquet et al. FEMS (in revision)