Project A01

Direct and indirect effects of multiple stressors in freshwater ecosystems on microbial parasites and scavengers

Hypothesis 1 ARC 2 AquaFlow ExStream Viruses Bacteria

Project leader

Prof. Dr. Alexander J. Probst

Project Summary

Freshwater ecosystems can be exposed to multiple stressors over time, some of them being imposed due to natural (e.g. seasonal) fluctuations, others due to human activity. While the effects of stressors on microbial community composition has been investigated for several freshwater ecosystems, the resulting impacts on microbial interactions including virus-host dynamics remains unexplored. Here, we propose to investigate the dynamics and interactions of microbial parasites, including viruses and microbial scavengers, and their potential hosts when exposed to multiple stressors in freshwater systems.

We will be part of the CRC’s central experiments in the AquaFlow and ExStream systems that are both populated by a variety of different forms of life. Three major stressors, temperature, salinity and hydrology, and their combinations will be used at different intensities to test the two following specific hypotheses: (SH A01-1) Eukaryotic viruses are heavily but indirectly affected by stressor increase and decrease, i.e. through the modification and abundance of their hosts, while (SH A01-2) Prokaryotic viruses (phages), microbial scavengers will strongly rely on biotic interactions with their hosts but their composite relative abundance in the ecosystem is stable throughout stressor increase and release.

To test for these hypotheses, we will leverage state-of-the-art genome-resolved metagenomics coupled to transcriptomics over time, stressor intensities and stressor combinations, whose respective experiments are carried out within project Z02. These data will be accompanied by quantitative PCR of specific 16S rRNA genes to determine accurate fluctuations of populations arising from stressors. The anticipated results create a generic understanding of the effect of multiple stressors on microbial parasites and scavengers.