Viral activity in subsurface sediments

• Applicant: Dr. Tim Engelhardt
• Subject Area: Palaeontology ; Microbial Ecology and Applied Microbiology ; Oceanography ; Virology
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 279186250

Microbial life in the marine deep biosphere is governed by extremely low energy fluxes and metabolic rates that allow turnover of biomass on the order of tens to thousands of years. As cells die, e.g. due to viral lysis, they contribute to the much greater pool of dead microbial biomass (necromass) that is very slowly degraded and help to sustain microbial life. Factors that control cell mortality are therefore important for the continued microbial life and biomass turnover in the deep subsurface. Anoxia and highly compacted sediments cause the absence of grazers and suggest viruses to be the main mortality factor. Viruses are highly abundant in subsurface sediments and can even exceed the number of prokaryotes. The activity of viruses and thus, their predicted impact on microbial life is yet not quantified but is an important factor to predict the virus-mediated biomass turnover and how life is controlled in the deep biosphere. In the proposed project, we will estimate the activity of viruses, their quantitative impact on the prokaryotic mortality and the virus-mediated carbon turnover in the deep subseafloor. The following questions should be answered: What is the quantitative impact of the viral activity on prokaryotic communities? What is the significance of the virus-induced cell turnover in respect to the estimated slow biomass turnover of deeply buried microbial communities? Do viruses facilitate a significant carbon and nutrient cycling (viral shunt) to support microbial life? To achieve our aims we combine direct imaging analyses of cells and viruses with modeling approaches to quantify the viral production in subsurface sediment. Herewith, we overcome common issues for activity estimates in subsurface sediments that are related to the very low microbial activity. Cultivation-based experiments with indigenous deep biosphere isolates will be performed with autotrophic and heterotrophic bacteria and will reveal the qualitative composition of organic material that is released by viral lysis of cells (viral shunt). This will answer a further question whether cell debris that is released during viral lysis of autotrophically grown bacteria promote heterotrophic growth? The in situ effect of the viral shunt will be predicted based on molecular quantification of specific viruses and host organisms in the sediment. This project will provide unique data that allow the integration of virus in quantitative estimates for microbial biomass turnover and the nutrient and carbon cycle in the marine deep biosphere.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 527: Bereich Infrastruktur - "International Ocean Discovery Program" (IODP)