Understanding the population dynamics of organisms exposed to the predatory activity of myxobacteria

Predatory myxobacteria have an antimicrobial nature that dominates their interactions with neighbouring organisms. They are abundantly found in soil, water, dung of herbivores, and have the potential to significantly affect the microbiome of an environment. In this project, we hypothesize that potential prey organisms evolve in response to the selective pressure exerted by predatory microbes. Using a variety of nutrient media, we isolated bacteria from soil samples to test their susceptibility and resistance to the laboratory strain Myxococcus xanthus DK1622 and its predatory secreted outer membrane vesicles (OMVs). Soil (with and without heat treatment) was spread onto plates which had been pre-inoculated with myxobacteria, OMVs, or no pre-treatment. Plates with myxobacteria lawns or OMVs exhibited reduced diversity of isolates compared to control plates. The yield and diversity of isolates obtained also depended on the media used. Heat pre-treated soil gave rise to distinct morphologies and fewer slime producers. Co-existence and competition were exhibited by soil isolates, which were identified using 16S rRNA gene sequencing and phylogenetic analysis. Purified isolates were also characterised for their resistance and/or susceptibility to predatory attack by a variety of myxobacteria. The bacterial isolates obtained varied when exposed to seven different myxobacteria predators. Our data suggest that the addition of myxobacteria to isolation plates biases isolation towards relatively predation-resistant prey organisms. Our next goal is to isolate myxobacterial predators from the same soil samples (on different prey isolates) and test predator-prey interactions quantitative using pure strains. The genetic basis of differential predatory activity and prey susceptibility can then be investigated.