Bacterial communities are globally ubiquitous and play critical roles in industry, human health, and the biosphere. Within these communities, resource variation, strong competition, and selective pressures are ever-present, driving bacteria to migrate and colonise fresh environments. Despite their importance, our understanding of microbial invasion is severely limited by experiments that focus on single species migration over short distances. These studies do not accurately represent bacteria migrating as communities within natural environments.
We examined the invasion of wastewater microbial communities as travelling chemotactic bands migrating continuously through fresh media using a novel chemotaxis tube experimental system. After one week of continual migration, we used metagenomic sequencing to assess taxonomic and functional shifts within the migrating communities. In addition, we used distributions of chemotaxis parameters to mathematically model the dispersal of bacteria within the experimental system. These models described the movement of bacterial cells and the subsequent uptake and diffusion of nutrients within a simulated environment.
Here, we observe nomadic communities, a subset of a microbial community that emerges from the whole microbial community and migrates together as a chemotactic band in the direction of nutrients. These nomadic communities contained thousands of chemotactic bacteria, viruses, and hitchhiking bacteria. Over the first 1 metre of migration, the migration speed of these nomads increased from 0.37 cm/hour to 0.81 cm/hour while the growth rate remained constant. The taxonomic composition of nomadic communities was variable, however, certain functions with known roles in bacterial migration were consistently high in abundance. Finally, the mathematical model of the tube system produced migrating bands, visibly similar to the bands observed experimentally, therefore demonstrating our understanding of the experimental system.
This study is the first to use a long chemotaxis tube experiment to investigate taxonomic and functional changes in co-migrating bacteria. We propose additional studies utilising the model systems presented for further study of migrating bacterial communities.