The deep ocean harbors immense microbial diversity with untapped genetic resources, yet coral-associated bacteria from Arabian Sea seamounts remain largely unexplored. This study investigated the diversity, functional potential, and biotechnological significance of bacteria associated with deep-sea corals, Enallopsammia rostrata and Flabellum sp., collected from seamount S8 (440 m) and plateau PT6 (1112 m) in the eastern Arabian Sea. A total of 217 bacterial isolates were obtained using seven different culture media, with actinobacterial enrichment media (ISP and AIA) yielding the highest recovery. The bacterial isolates were predominantly Gram-negative across all samples (52–58%), with morphological characterization revealing 70 distinct morphotypes. Comprehensive functional screening demonstrated remarkable variability in biofilm formation (0.056–1.177 a.u.), laccase activity (0.000–0.095 U/mL), tyrosinase activity (0.05–2.88 μg/mL), melanin production (0.045–5.561 mg/mL), UV absorption (0.097–2.242 a.u.), and antioxidant activity (47.33–81.83%). Notably, isolates from Flabellum sp. collected from plateau PT6 (T2) exhibited the highest antioxidant potential (81.83%) and the strongest biofilm-forming community (52% moderate to strong producers), while those from Flabellum sp. collected from plateau PT6 (T1) showed the highest median laccase activity (0.018 U/mL) and the greatest tyrosinase variability. The discordant relationship between laccase activity and quinone assay revealed that some bacteria contribute to the degradation of recalcitrant organic compounds, while others are primarily involved in melanin biosynthesis for oxidative stress protection, highlighting their ecological significance in extreme deep-sea environments. Molecular identification of high-performing isolates using 16S rRNA gene sequencing revealed the dominance of genera such as Acinetobacter, Halomonas, Shewanella, Pseudomonas, and Psychrobacter. All purified isolates have been deposited in the Marine Microbial Reference Facility (MMRF, www.mmrf.nio.res.in) at CSIR-NIO, Kochi, contributing to the cataloging of deep-ocean microbial genetic resources for sustainable utilization and governance in alignment with the BBNJ Agreement. This marks the first comprehensive functional profiling of seamount coral-associated bacteria from the Arabian Sea identifies promising resources for pharmaceutical, cosmetic, and industrial applications while advancing understanding of host-microbe interactions in extreme deep-sea ecosystems.

Keywords: Deep-sea corals, seamount, Arabian Sea, coral-associated bacteria, melanin, laccase, antioxidant, MMRF, BBNJ