Abstract
Healthy coral-associated bacteria produce antimicrobial compounds that can inhibit disease-causing pathogens. This biocontrol potential is particularly relevant in combating White Syndrome (WS), a deadly coral disease. This study aimed to identify beneficial bacteria from healthy corals that could serve as WS control agents. Healthy and WS-infected coral samples were collected from Sawopudo waters, Southeast Sulawesi, Indonesia. Bacteria were isolated using spread and streak plate techniques, and their antibacterial activity was assessed in vitro via agar plug assays. Isolates with strong inhibition zones were identified by 16S rRNA gene sequencing. The most promising strains were tested in vivo by inoculating WS-infected corals with candidate bacteria. Of six isolates with notable antimicrobial activity, the most active showed high similarity to Bacillus tequilensis, Micrococcus luteus, Cytobacillus firmus, Staphylococcus arlettae, and Priestia aryabhattai (similarity 99.43%–99.93%). Cytobacillus firmus demonstrated the strongest in vivo efficacy, forming a 16.6 mm inhibition zone and restoring up to 20% of infected coral tissue. These results underscore the potential of probiotic bacteria as a sustainable strategy to mitigate WS and protect coral reef ecosystems.