| Abstract: | A recently available transposition system was utilized to isolate a nonmotile mutant of the coral-bleaching pathogen Vibrio coralliilyticus. The mutation was localized to the fhlA gene, and the mutant lacked flagella. The flhA mutant was unable to exhibit chemotaxis toward coral mucus or to adhere to corals and subsequently cause infection.Coral reefs have been described as the rain forests of the sea due to their enormous biodiversity. Unfortunately, during the past few decades nearly 30% of the worldwide coral population has been severely damaged by various diseases (9). Coral bleaching is a disruption of the Symbiodinium-coral symbiosis and results in “whitening” of the coral due to the loss of the Symbiodinium symbiont or its pigment. On a global scale, bleaching is one of the major coral diseases (5) and tends to correlate with increased seawater temperatures (10). Thermal stress is the generally accepted hypothesis to explain the mechanism of the disease. In the last several years, bacterial bleaching of corals has been suggested as an alternative hypothesis to explain some coral bleaching episodes (21, 22). Vibrio shiloi was the first bacterium shown to be a causative agent of coral bleaching in the Mediterranean coral Oculina patagonica (13, 14). More recently, Vibrio coralliilyticus has been reported to be the causative agent of temperature-induced bleaching of Pocillopora damicornis (3, 4) and white syndrome in Indo-Pacific corals (25). Thus, infections by V. coralliilyticus could have an impact on global coral health.Chemotaxis and flagellum-mediated motility allow bacteria to pursue nutrients and to reach and maintain their preferred niches for colonization (7, 8). Several Vibrio species (both pathogens and symbionts) require functional flagellum-mediated motility to invade their hosts and establish successful colonization (17, 18, 27, 28).In this study, we utilized a recently available Tn5-based transposition system to isolate a nonmotile mutant of the coral-bleaching pathogen V. coralliilyticus. The mutation was localized to the gene flhA. Here we demonstrate that the flagellum is critical for chemotaxis toward coral mucus, adhesion to the corals, and infection by V. coralliilyticus. |
