Effects of viral activity and of viral lysis mediated recycling of organic carbon on the bacterial and viral communities in marine pelagic systems

Although the number of viruses exceeds by far the number of all other plankton components, the role of viruses in the interactions between phytoplankton, dissolved organic carbon (DOC) and bacterioplankton is not understood sufficiently yet. Bacterial viruses cause up to 50 % of the bacterial mortality. Model analyses show that viruses contribute to the maintenance of the diversity of the bacterial community, by infecting mainly highly abundant, competitive bacterial strains. Viral lysis of bacterial cells also causes the release of organic carbon and its reintroduction into the dissolved organic carbon pool. The effects of this carbon recycling are not known yet. This makes the role of viruses one of the most intriguing research tasks in aquatic microbial ecology. The aim of this project is to monitor the structure as well as the specific activity patterns of bacterioplankton communities under virus-enriched conditions. While the current view on viral lysis effects on the bacterioplankton community largely focuses on changes in diversity patterns, the present proposal carries this focus a step further: We hypothesize that the release of bacterial carbon by viral lysis has a significant impact on the structure of the bacterial community. Thus, it is essential to link the effects of viral lysis on bacterial diversity to the effects of viral lysis derived substrate on the specific activity of non-infected bacterial strains. The availability of this substrate may favour bacterial groups, which are able to utilize complex organic molecules efficiently, thereby causing a shift in the bacterial community to groups, which are known to degrade complex polymers. Insights in the effects of this linkage between viral lysis and bacterial community composition are especially important for the understanding of microbial carbon cycling and degradation processes in environments with low concentrations of readily available phytopankton derived carbon. This includes areas in surface waters with temporarily or constantly low primary production as well as the aphotic zone of the oceans.