The relative importance of viral lysis and nanoflagellate grazing for prokaryote mortality in temperate lakes

Abstract

1. We explored the factors that potentially affect viral abundance, viral life strategies (lytic versus lysogenic cycle) and the relative importance of viral lysis and heterotrophic nanoflagellate grazing for prokaryote mortality in the euphotic zone of 19 freshwater lakes in a single geographical region (the French Massif Central). 2. Flow cytometry indicated that viral abundance ranged from 0.5 to 26.3 9 10 7 viruses mL À1 , exceeding prokaryote abundance by c. 16-fold on average. Multiple regressions revealed that prokaryotic abundance was the best predictor of viral abundance (r 2 = 0.74), suggesting that the prokaryotes were the major hosts for viral proliferation in these lakes.3. Viral life strategies varied with month of sampling (June, July, August 2010). Lytic infection was the prominent mode of viral infection in June and August, whereas lysogenic infection was more evident in July in the majority of sampled lakes. This temporal shift in viral strategy was controlled by the availability of phosphate and chlorophyll concentration via host cell growth, with high concentrations favouring lytic infection and low concentrations favouring lysogenic infection. Such antagonistic interactions between viral life strategies support the hypothesis that lysogeny may represent a survival strategy for viruses in harsh nutrient/host conditions. 4. The dominance of viruses over flagellates, or vice versa, as prokaryotic mortality factors differed between the lakes. By taking into account both forms of mortality, our study indicates that viruses and flagellates are likely to act additively in their effects on prokaryotes by regulating the proportion of the most active members of the prokaryotic community. Such a combined effect of viruses and flagellates may strongly influence the planktonic food web and whole-ecosystem functioning.

Viral-Induced Mortality of Prokaryotes in a Tropical Monsoonal Estuary

“…A study by Parvathi et al (2013) on CE has attributed short-term variations in VP to various host processes and environmental factors, including light and salinity. The above findings are corroborated in this study with significant correlation ( p < 0.001) of VA with PA and BP, as previously reported for different environments (Parvathi et al, 2011; Winget et al, 2011; Payet and Suttle, 2013; Pradeep Ram and Sime-Ngando, 2014). The host parameters were influenced by seasonal salinity variations, which in turn triggered the spatial and seasonal variations in viral parameters.…”

Chemical multi-contamination drives benthic prokaryotic diversity in the anthropized Toulon Bay

“…Thus, a significant part of this variability remained statistically unexplained in our study, corresponding to some abrupt shifts that were observed in close and chemically similar sampling sites. This could be partly due to biotic factors, such as predation or viral lysis pressures, which are well known for their influence on prokaryotic community abundance and structure (Ben Said et al, 2015;Louati et al, 2013;Ram et al, 2014;Sauret et al, 2015) but…”

High-resolution metagenomic reconstruction of the freshwater spring bloom

“…Estimation of doubling times as performed here (both using CARD-FISH or metagenomic abundances) was done according to the following assumptions: Firstly, estimates of average mortality by grazing (24%) and by viruses (31%) were obtained from prior observations from a relatively large sample of 19 lakes [ 68 ]. Taken together, a total of 55% mortality was assumed as a combined effect.…”