Presence and Role of Prokaryotic Viruses in Groundwater Environments

Abstract

This chapter aims to give a condensed overview on the occurrence and potential roles of prokaryotic viruses (phages) in groundwater. While abundant and steadily growing data on marine and limnic surface habitats underscores the significance of phages for biogeochemical cycling and microbial community dynamics, research tapping into the ecology of phages in groundwater is extremely scarce. Here, we summarize the findings of the few available studies and discuss potential driving factors of viral abundance and activity based on published and yet unpublished datasets. Further, based on established mechanisms of phage host interactions, such as the ‘viral shunt,’ the ‘Kill-the-Winner’ dynamics and the modulation of host metabolisms via auxiliary metabolic genes, we propose (largely hypothetical) roles of phages in groundwater. Due to the nutrient and energy-limitation of aquifers, we might expect a high frequency of stalled or slowly progressing viral infections in groundwater. Yet, recent metagenomic and metatranscriptomic evidence as well as flow cytometric quantification of virus-like particles indicate that viruses in subsurface environments are not just persisting but are indeed involved in major biogeochemical cycles, particularly in recently recharged groundwater. Finally, although the few studies available confirm a dominance of tailed phages as in surface waters, also other groups such as Microviridae and Inoviridae may play an important role in the subsurface. Upcoming research will allow to evaluate, extend and refine these exciting early evidence and hypotheses.