Table 1.

Summary of previous work on viral abundance, activity, and diversity in various environments of the deep subsurface biosphere, deep ocean, and sediments.

Environment	Work on viruses to date	Reference
Surface marine sediments	High viral production in benthic ecosystems: may be responsible for up to 80% of cell mortality, thus releasing large amounts of carbon through the “viral shunt.” Viral diversity in sediments is fairly high, and showed a higher incidence of lysogenic than lytic phages	Danovaro et al. (2008), Middelboe et al. (2006), Siem-Jørgensen et al. (2008), Breitbart et al. (2004)
Deep sediments	Viral and bacterial abundance and production decrease exponentially with depth in sediments, up to 96 mbsf	Middelboe et al. (2011), Bird et al. (2001), Engelhardt et al. (2011)
	Mitomycin C experiments revealed that 46% of isolates contained inducible prophage
Deep basalt	None known
Deep granitic groundwater	Viruses are present and correlated with bacterial abundance (ratio of ∼10:1), similar to many surface environments	Kyle et al. (2008)
Diffuse flow hydrothermal fluid	Lysogeny appears to be a dominant lifestyle among vent viruses; viruses in diffuse flow are capable of infecting a wide range of hosts across domains and thermal regimes	Williamson et al. (2008), Anderson et al. (2011)
Cold seeps/methane hydrates	Viral activity and abundance vary among seeps, with a virus to prokaryote ratio ranging between relatively low (<0.1) to relatively high (66.36)	Middelboe et al. (2006), Kellogg (2010)
Deep-water column	Viral abundance generally tracks bacterial abundance, but the virus:cell ratio at depth varies. In some areas, the ratio increases with depth	Hara et al. (1996), Parada et al. (2007), Steward and Preston (2011)
	Metagenomic work characterizing viral diversity found most viral sequences had matches to bacteriophages in the Podo-, Sipho-, and Myoviridae, with a few hits to eukaryotic sequences