Assessing the Influence of HGT on the Evolution of Stress Responses in Microbial Communities from Shark Bay, Western Australia.

Pustular microbial mats in Shark Bay, Western Australia, are modern analogs of microbial systems that colonized peritidal environments before the evolution of complex life. To understand how these microbial communities evolved to grow and metabolize in the presence of various environmental stresses, the horizontal gene transfer (HGT) detection tool, MetaCHIP, was used to identify the horizontal transfer of genes related to stress response in 83 metagenome-assembled genomes from a Shark Bay pustular mat. Subsequently, maximum-likelihood phylogenies were constructed using these genes and their most closely related homologs from other environments in order to determine the likelihood of these HGT events occurring within the pustular mat. Phylogenies of several stress-related genes-including those involved in response to osmotic stress, oxidative stress and arsenic toxicity-indicate a potentially long history of HGT events and are consistent with these transfers occurring outside of modern pustular mats. The phylogeny of a particular osmoprotectant transport gene reveals relatively recent adaptations and suggests interactions between Planctomycetota and Myxococcota within these pustular mats. Overall, HGT phylogenies support a potentially broad distribution in the relative timing of the HGT events of stress-related genes and demonstrate ongoing microbial adaptations and evolution in these pustular mat communities.