The marine deep biosphere represents the largest biotope on Earth. Throughout the last years, we have obtained interesting insights into its microbial community composition. However, one component that was completely overlooked so far is the viral inventory of deep-subsurface sediments. As grazers probably play only a minor role in anoxic and highly compressed deep sediments, viruses might be the main "predators" for indigenous microorganisms. Furthermore, the viral shunt could have a major impact on the deep biosphere in providing labile organic compounds to the microbial community in this generally nutrient depleted habitat.
From cultivation experiments on samples recovered during ODP Leg 201 and IODP Exp. 301 we have obtained large culture collections of deep-biosphere isolates. These culture collections represent an archive of the viral composition within the deep biosphere as up to 70% of cultivated bacteria contain prophages within their genome. In six out of thirteen representative isolates, prophages were induced to form free virus-particles that will be analysed in detail due to their morphologic and phylogenetic diversity.
In this project, we will identify the phage inventory of the deep biosphere by ecophysiological studies on ODP/IODP isolates to answer the following questions: To which extent are deep-biosphere populations controlled by viral infections? What is the inter- and intraspecific diversity and the host-specific viral biogeography? Can viral infections tell us something about the physiological state of indigenous microorganisms? Finally, we will obtain estimates for the viral shunt as an important factor for sustaining the deep biosphere.
Engelen B, Engelhardt T, Cypionka H (2014) Phagen in Sedimenten der marinen
tiefen Biosphäre. Biospektrum 04.14:380-382, DOI: 10.1007/s12268-014-0451-0
Engelhardt T, Kallmeyer J, Cypionka H, Engelen B (2014) High virus-to-cell ratios indicate on-going production of viruses in deep subsurface sediments. ISME J 8:1503–1509
Engelhardt T, Sahlberg M, Cypionka H, Engelen B (2013) Biogeography of Rhizobium radiobacter and distribution of associated temperate phages in deep subseafloor sediments. ISME J 7:199-209
Engelhardt T, Sahlberg M, Cypionka H, Engelen B (2011) Induction of prophages from deep-subseafloor bacteria Environm Microbiol Rep 3:459–465