Lytic failure in cross-inoculation assays between phages and prokaryotes from three aquatic sites of contrasting salinity

Abstract

Little is known about the ability of phages to successfully colonize contrasting aquatic niches. We conducted experimental cross-infections between viruses and prokaryotes from three tropical sites of West Africa, with distinct salinities: a freshwater reservoir, a marine coastal station and a hypersaline lake. A cellular poison-based method (potassium cyanide) revealed that the addition of native viruses (regardless of the water type) consistently stimulated viral production. Conversely, in all incubations conducted with allochtonous (non-native) viruses, their overall production was not promoted, which suggests a lytic failure. Prokaryotic heterotrophic production increased in fresh and marine water supplemented with native viruses, but not in the hypersaline water. These results point to the role of the viral shunt in low-salinity environments, where the release of bioavailable lysis products might be of high nutritional value for the noninfected prokaryotes. In contrast, in hypersaline water where glycerol is a major carbon and energy source for the heterotrophic community, dissolved organic matter (DOM) of lytic origin may represent a less important DOM source for prokaryotes. Finally, our results suggest that cosmopolitan phages capable of moving between biomes are probably rare in aquatic habitats, supporting the common idea that most wild phages are relatively limited in their host range.

Culture-Independent Approaches for Studying Viruses from Hypersaline Environments

“…1 for an example). In the transition to the most concentrated systems, over 25% total salts, a sharper increase in virus concentration can be observed, as reported for Mediterranean coastal multipond solar salterns (26) and a series of natural systems in Senegal covering salinities from brackish to near salt saturation (12). This increase may be due to the lack of bacterivory or very low abundances (2 ϫ 10 5 to 3 ϫ 10 5 per liter) of nanoflagellate predators reported for these two analyzed systems.…”

“…This finding is in agreement with the work by Dinsdale et al (21) that carried out a functional metagenomic profiling of nine different biomes (subterranean, hypersaline, marine, freshwater, coral associated, microbialites, aquaculture, fish associated, terrestrial animal associated, and mosquito associated) and found differences between them that predicted the biogeochemical conditions of each environment. This difference between halophilic viruses and those from fresh and marine waters was also demonstrated by the lytic failure observed while viruses from nonextreme systems were used to infect the prokaryotic community present in Lake Retba samples (12). The authors interpreted these results based on the differences among viruses infecting Bacteria (that dominate many marine and freshwater habitats) and Archaea (that dominated the Lake Retba community).…”

“…However, this cannot be generalized to all hypersaline systems, since high numbers (7 ϫ 10 6 to 28 ϫ 10 6 per liter) of heterotrophic and extremely halophilic grazers actively ingesting prokaryotes have been described in 31% salt waters in a solar saltern located in western South Korea (40). In addition, viral persistence in water is positively correlated with salinity, with rates of persistence above 97% in close-to-saturation waters (12).…”

“…The reason for this abundance is intriguing, although there are basically two hypotheses for explaining this phenomenon: these high numbers are due either to the physical stability of viruses in high-salt systems or to the high viral production reached in these systems (12,57). When analyzed along a salinity gradient (from marine or freshwater to extremely hypersaline, salt-saturated environments), the number of viruses, which is normally correlated to the number of cells, increases with salt (see Fig.…”

Coral Mucus Is a Hot Spot for Viral Infections

“…Given the high viscosity and the small volumes of mucus available (Ͻ10 ml), we could not apply the viral reduction approach to estimate viral lytic production rates (57). Then, the KCN method, a cellular poison used to stop viral production, emerged as the best compromise (46,55,56). The results obtained with this method revealed that lytic infections are actually widespread in coral mucus.…”