Survival of surface bacteriophages and their hosts in in situ deep-sea environments

Abstract

ABSTRACT Through particles sinking as well as the movement of water masses, a fraction of bacterioplankton and virioplankton can be transported vertically from the surface to the deep oceans, and display significant changes in viral–bacterial interactions. The survival and activity of the sinking prokaryotes and viruses in the deep-sea environment is crucial for our understanding of deep-sea ecosystems and biogeochemical cycles. However, due to the substantial challenge involved in situ deep-sea incubation, the effect of the deep-sea environments on the ecology of surface prokaryotes and viruses is poorly studied. To fill this knowledge gap, we used an in situ deep-sea long-term incubation device to examine the effect of the natural deep-sea environment on the stability and activity of four viruses and their hosts ( Prochlorococcus , Synechococcus , and heterotrophic bacteria) isolated from the surface ocean. Our results showed that viral particles had still not decayed completely after in situ incubation for 1 year, with an average retention rate of 5.69% ± 5.13% (ranging from 1.25% to 13.06%) for infectivity and 68.11% ± 40.50% (ranging from 8.55% to 99.08%) for particles. This suggests that surface viruses probably retain long-term infectivity after sinking and may influence deep-sea microbial populations in terms of activity, function, diversity, and community structure through viral–bacterial interactions and ultimately affect deep-sea biogeochemical cycles. IMPORTANCE The survival of the sinking prokaryotes and viruses in the deep-sea environment is crucial for deep-sea ecosystems and biogeochemical cycles. Through an in situ deep-sea long-term incubation device, our results showed that viral particles and infectivity had still not decayed completely after in situ incubation for 1 year. This suggests that, via infection and lysis, surface viruses with long-term infectious activity in situ deep-sea environments may influence deep-sea microbial populations in terms of activity, function, diversity, and community structure and ultimately affect deep-sea biogeochemical cycles, highlighting the need for additional research in this area.