Viral infections as controlling factor of the deep biosphere

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Viruses might be the main “predators” in the deep biosphere and possibly have a major impact on indigenous microorganisms in providing labile organic compounds for this extremly nutrient depleted habitat. While direct counting of viruses along depth profiles of various ODP sites indicated a general decrease with depth, we could show that the ratio of viruses vs. cells increased. Prophages were induced from six out of thirteen representative deep-biosphere bacteria of our ODP Leg 201 culture collection, exhibiting different morphotypes of sypho- and myoviruses. Five of them were subjected to whole genome sequencing. This sequence information will be used to design specific primers for a molecular detection and quantification of these phages in the deep biosphere. Especially the number and distribution of phages that infect Rhizobium radiobacter, which is highly abundant in subsurface sediments, will be examined. We will further focus on the following questions: How important is the viral shunt in providing essential nutrients for deep biosphere populations? How is the physiological state of indigenous microorganisms related to viral infections?