Evolution of hunt, kill, devour in a Vibrio ecospecies

Bacterial ecospecies are a recently recognized genetic structure that is hypothesized to arise by complex adaptation to a new niche. Using coadaptation analysis as a foundation for laboratory experiments, we find that the ecological strategy of the “Molassodon” ecospecies of Vibrio parahaemolyticus is to hunt, kill and devour bacterial prey in viscous liquids. Instead of swarming on surfaces, Molassodon strains have differentiated and repurposed their lateral flagella to enhance swimming. We functionally link Type VI secretion and nutrient uptake to this motility phenotype and reconstruct the evolution of Molassodon, showing that several key genes have been imported from other Vibrio species. Our analysis confirms the functional coherence of bacterial ecospecies and provides a window into adaptation for environmental microbes, where characterizing relevant microhabitats and evolutionary strategies remains a considerable challenge.