FIG 8.

Model depicting how Vibrio competition triggers their virulence over coral hosts. We propose that the synergism observed in coinoculated corals was caused by increases in Vibrio virulence as a consequence of competition sensing mechanisms. Vibrio coral pathogens within corals exist in close proximity with many taxa, and their interactions define the pathogenic potential of the entire community. Vibrio spp. can respond to competition by attacking via the T6SS or by defending themselves through induction of stress responses. In addition, Vibrio spp. produce siderophores that are involved in biofilm formation, swarming motility, and toxin production. These mechanisms, activated by competition sensing, may confer an advantage to Vibrio coral pathogens that enables them to survive in host tissue and degrade the tissue as collateral damage.