Virus-integrated laboratory models for habitability studies of Enceladus, Europa, and Titan.

Biogeochemical models have become critical for answering questions about the habitability of ocean worlds, especially that of early Earth. However, when extended to icy moons, experimental biogeochemical systems become especially challenging. Due to less constrained physicochemical parameters extrapolated from former flybys, the most comprehensive approaches could combine experimental and computational models of proposed ocean conditions with microbes present. This minireview makes the case for needing to also include viral/phage interactions with microbial models as a mechanism for maintaining biogeochemical cycling. The viral shunt, or the release and recycling of organic/inorganic matter in aquatic ocean systems via the viral lysis of bacteria and archaea, has proven to be a critical source of carbon/sulfur/iron cycling throughout Earth's oceans. Nonetheless, the viral shunt remains understudied in the realm of other ocean world astrobiology and habitability studies but may provide a mechanism for detection of organics by future missions. The current knowledge of physicochemical conditions on three ocean worlds (Enceladus, Europa, and Titan) is briefly summarized in this work to contextualize examples of Earth-based integrated archaeal viruses (Pyrobaculum filamentous virus, Sulfolobus turreted icosahedral virus, and Methanosarcina spherical virus) that may be suitable for habitability studies for virus-integrated biogeochemical ocean world models.