Functionally Diverse Coral-Associated Bacteria from an Urban Reef Exhibit Antioxidant and Antibiofilm Properties Relevant to Probiotic Development

Coral reefs are increasingly threatened by environmental stressors, resulting in substantial ecological losses. Yet, resilient coral reef systems—such as urban reefs—offer a promising reservoir of beneficial microorganisms capable of supporting coral health under stress. In this study, we characterized, and functionally screened bacteria associated with an urban reef dominated by the coral Madracis auretenra . From 22 previously selected isolates, all exhibited catalase activity, with several showing notably high levels. Pigmented strains likely produce carotenoids with potential photoprotective and antioxidant functions. Most isolates inhibited biofilm formation in multiple reporter strains. While quorum sensing inhibition, and antagonism against Vibrio coralliilyticus were observed, both effects were generally low, suggesting that suppression of pathogens may occur primarily through interference of biofilm formation rather than direct inhibition. Growth kinetics revealed strain-specific dynamics, with fast-growing isolates offering potential advantages for probiotic application. Multidimensional functional profiling indicated trait overlap and redundancy among strains, reflecting niche specialization and the co-expression of multiple beneficial traits—features desirable for the design of stable probiotic consortia. These findings underscore the probiotic potential of bacteria associated with urban M. auretenra , particularly for traits related to oxidative stress mitigation and microbial regulation. Further in vivo validation is needed to assess their efficacy under reef-relevant stress conditions.