Co-migration of hundreds of species over metres drives selection and promotes non-motile hitchhikers

Prokaryotes dominate the biosphere and form diverse communities disrupted by invasion. Invaders and remaining community members experience resource surfeit, competition, and selective pressures. Little is known about invasion in natural microbial communities. We examined invasion by chemotaxis in a meso-tube system at taxonomic, functional, and genomic levels as communities sank, rose, and formed a chemotactic band that migrated for metres. The band velocity increased as the community migrated despite non-motile bacterial hitchhikers and up to 10⁶ viruses/ml. Migrating communities left complex residual communities in their wake, showing dynamic taxonomic composition and adaptation through increased migration-associated genes. Approximately 500 species migrated together, competing for dominance. This system offers a superior method for studying band and residual community dynamics, bacterial hitchhiking, viral transport, gene evolution, and survival strategies, revealing cohesive communities that persist over extended distances. Our methods and results provide an experimental foundation for investigating microbial invasion in multiple ecological settings.