Effect of seawater–freshwater cross-transplantations on viral dynamics and bacterial diversity and production

Abstract

Dilution experiments were carried out to investigate the community composition and the metabolic response of seawater and freshwater bacteria to cross-transplantation, and the effects of non-indigenous bacterial hosts on viral dynamics. Changes in viral and bacterial abundance and production, as well as bacterial respiration, carbon demand and diversity were regularly monitored over a 6 d period. Bacterial production in the transplanted seawater (SB-t) and freshwater (FB-t) bac- teria treatments was stimulated up to 256 and 221%, respectively, compared to controls. The stimu- lation of bacterial production and carbon demand was accompanied by a decrease in bacterial rich- ness. Net viral production was stimulated by 81% in SB-t and repressed by 75% in FB-t. Transplantation increased the virus-induced mortality of marine bacteria, but decreased it for fresh- water bacteria. These results suggest that (1) marine bacteria can readily oxidize freshwater dis- solved organic matter, and (2) freshwater viruses might be able to infect marine hosts, thus highlight- ing their potential role in fueling bacterial growth under resource stress or nutrient-depleted conditions.