Stability and infectivity of allochthonous viruses in deep sea: A long-term high pressure simulation experiment

The bathypelagic zone is a large, dark, cold, high-pressure environment that undergoes extensive material and energy exchanges with the upper ocean and the deep biosphere. Viruses are important parts of the deep ocean, and transportation of surface viruses has been considered as an important source of deep-sea viruses. However, limited information is available about the activity and decay of surface viruses in the deep-sea ecosystem. Therefore, this study investigated the stability of representative viral isolates of three morphological types with different sizes infecting autotrophic and heterotrophic bacteria by incubation in the dark under high hydrostatic pressure (HHP) of 30 MPa (corresponding to the pressure at a depth of about 3000 m) and 4 °C for two years. Cyanophage S-CBP1 and two roseophages, RDCBΦ1 and vB_DshS-R4C, were able to infect their hosts after long-term incubation under HHP. However, cyanophages S-CBWM1 and S-SCSM1, as well as roseophages RDCBΦ3 and vB_DshP-R2C, decayed and/or inactivated completely. The sensitivity of viral isolates to HHP might be related to their morphological characteristics, especially their capsid sizes. In addition, HHP treatment of environmental viral populations showed 92.2% reduction of low-fluorescence viruses and total loss of high-fluorescence viruses. The first experimental evidence from this study showed a large variability in the pressure effects on the stability and infectivity of different viruses and suggests that viruses isolated from the ocean's surface may survive under deep-sea conditions.