Co-cultivation rescues suicidal <i>Paenibacillus amylolyticus</i> swarms

Bacterial locomotion is integral to acquiring resources and getting access to new niches. Swarming, a type of motility where flagellated bacteria cooperatively move together across a semi-solid surface, is one example of how bacteria can colonize new territories. This collective behavior is temporally and spatially orchestrated, requiring task specialization of community members. In this study, we paired a swarming bacterium, Paenibacillus amylolyticus, with a non-swarmer, Stenotrophomonas maltophilia, to investigate the impact on fitness of each strain. In dual-species conditions, the community swarm became significantly thicker and improved the ability of S. maltophilia to range into new territories. Swarming enabled P. amylolyticus to cross barriers of antimicrobials, whereas the thicker, dual-species swarm did not empower S. maltophilia to cross. Comparative studies of population dynamics revealed that over time, monospecies swarms of P. amylolyticus entered a state unable to grow despite still showing reductase activity. However, in a dual-species swarm, S. maltophilia rescued P. amylolyticus from this state. This rescue is attributed to the pH stabilization that occurs in this two-species combination, where S. maltophilia alkalizes the environment, thereby providing a more favorable environment for P. amylolyticus.