The dynamics of evolution - how horizontal gene transfer drives the diversification and adaptation of complex microbial communities in marine ecosystems

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Marine bacteria and archaea represent the major part of the total biodiversity on Earth. These microorganisms are main drivers of biogeochemical cycles in the marine realm and thus play an integral role in ecosystem stability and functioning. Several recent studies targeted the diversity of marine microorganisms and their response to changing environmental conditions. However, our knowledge about genetic diversification of natural microbial communities and their genomic adaptation to environmental stresses is still rather limited. The aim of this project is to understand the dynamics of microbial evolution in marine ecosystems. As horizontal gene transfer is thought to be the major driver of microbial evolution, the main question to be answered is how horizontal gene transfer drives the diversification of complex microbial communities in marine ecosystems and their adaptation to prevailing environmental stresses. To assess microbial community dynamics, samples will be taken repeatedly in three coastal areas of Australia, where microbial communities are threatened by various stressors including risen water temperatures and agricultural run-offs. Data on environmental properties will be measured simultaneously. Environmental DNA will be extracted from obtained sampling material. As horizontal gene transfer is likely to occur in dense microbial communities, DNA isolated from host-associated microbial communities including the seaweed holobiont will be subjected to next-generation sequencing, and obtained metagenomic datasets will be subsequently mined for mobile genetic elements transferred by horizontal gene transfer. In addition to data on environmental properties and horizontal gene transfer, changes in taxonomic composition as well as species richness of free-living, host-associated and sediment microbial communities will be assessed by sequencing of 16S rRNA genes amplified from environmental DNA. The generated data will be statistically evaluated to decipher the dynamics of microbial evolution in marine ecosystems with emphasis on microbial diversification and adaptation. The final outcome of this project will provide insights into short-term genetic diversification of complex microbial communities and the relation to environmental adaptation. This is important as it will define the adaptability of microorganisms and microbial communities to environmental stressors and will allow a prediction of how these systems will respond to current and future ecosystem changes, e.g., induced by pollution and global warming, respectively.