High Lytic Infection Rates but Low Abundances of Prokaryote Viruses in a Humic Lake (Vassivière, Massif Central, France)

Abstract

We explored the abundance and infection rates of viruses on a time series scale in the euphotic zone of the humic mesotrophic Lake Vassivière (Massif Central, France) and compared them to nonhumic lakes of contrasting trophy (i.e., the oligomesotrophic Lake Pavin and the eutrophic Lake Aydat) located in the same geographical region and sampled during the same period. In Lake Vassivière, the abundances of virus-like particles (range, 1.7 ؋ 10 10 to 2.6 ؋ 10 10 liter ؊1 ) were significantly (P < 0.001) lower than in Lakes Pavin and Aydat. The percentage of virus-infected prokaryotic cells (mean, 18.0%) was significantly higher (P < 0.001) in Vassivière than in Pavin (mean, 11.5%) and Aydat (mean, 9.7%). In Vassivière, the abundance of prokaryotes was a good predictor (r ‫؍‬ 0.78, P < 0.001) of the number of virus-like particles, while the potential grazing rate from heterotrophic nanoflagellates was positively correlated to the viral infection rate (r ‫؍‬ 0.75, P < 0.001; n ‫؍‬ 20), indicating the prevalence of cycling interactions among viruses, prokaryotes, and grazers, which is in agreement with past experiments. The absence of correlation between chlorophyll a concentrations (Chl) and viral parameters suggested that the resources for the lytic activity of viruses in Vassivière were mainly under allochthonous control, through host activity. Indeed, compilation of data obtained from several nonhumic lakes in the French Massif Central revealed that Chl was positively correlated to the abundance of virus-like particles at concentrations above 0.5 g Chl liter ؊1 and negatively at concentrations below 0.5 g Chl liter ؊1 , suggesting that phytoplankton-derived resources could force prokaryotic growth to attain a certain threshold level when the host availability is sufficient to boost the proliferation of viruses. Therefore, based on the high level of lytic infection rates in Lake Vassivière, we conclude that viruses are key agents for prokaryotic mortality and could influence the food web dynamics in humic lakes, which may ultimately depend on the internal cycling of resources and, perhaps, mainly on the allochthonous inputs and the associated humic substances.

Seasonal Variation in Viral Infection Rates and Cell Sizes of Infected Prokaryotes in a Large and Deep Freshwater Lake (Lake Biwa, Japan)

“…This suggests that although viral infection in the surface layer leads to a lower number of intracellular viral particles (one-third that in the deeper layer, Table 1 ), and viral abundance is supported by a high infection rate and high prokaryotic production. Compared to previous studies conducted in Lake Créteil (France) and Lake Vassivière (France), our result (mean FIC: 15.1%) was lower than that in Lake Créteil (FIC: mean, 32.0%) and similar to that in Lake Vassivière (FIC: mean, 17.6%; Pradeep Ram et al, 2010a , 2011 ). This could be explained in the same way.…”

“…This could be explained in the same way. Lake Vassivière is mesotrophic like Lake Biwa, and these lakes had similar prokaryotic and viral abundances, resulting in similar estimated contact rates (174 contacts cell −1 d −1 ) and FIC values ( Pradeep Ram et al, 2011 ). However, in Lake Créteil, prokaryotic and viral abundances were higher than in Lake Biwa, resulting in much higher estimated contact rates (549 contacts cell −1 d −1 ).…”

A New Freshwater Cyanosiphovirus Harboring Integrase

“…Viral morphology and burst size (BS) were determined by transmission electron microscopy (TEM) as described in Pradeep-Ram et al (2011) . Briefly, viruses and cells were diluted in 0.002-mm filtered-distilled-deionised water and collected onto a 400-mesh Cu electron microscopy grid supported with carbon-coated Formvar film (Pelanne Instruments, Toulouse, France) by ultracentrifugation at 70,000 × g for 20 min at 4°C using a SW40Ti rotor in a Beckman LE-80K ultracentrifuge (Brea, CA, United States).…”

Dynamics of Viral Abundance and Diversity in a Sphagnum-Dominated Peatland: Temporal Fluctuations Prevail Over Habitat

“…Through lytic and lysogenic life cycles, viruses affect the metabolism and abundance of their cellular hosts from all three domains of life (synthesis in) ( Kirchman, 2012 ), impacting the diversity and the structure of microbial communities ( Middelboe, 2000 ; Suttle, 2007 ; Sime-Ngando, 2014 ). Because viruses function as a top-down control on microbial production ( Pradeep Ram et al, 2011 ; Chow et al, 2014 ), they affect biogeochemical cycles through the release of substantial amounts of organic carbon and nutrients in the environment ( Middelboe and Lyck, 2002 ). While resources released by this viral shunt can be reused to sustain microbial biomass, it typically results in a reduction of the overall flow of organic matter and energy towards higher trophic levels ( Fuhrman, 1999 ; Middelboe and Lyck, 2002 ; Ankrah et al, 2014 ).…”