Microbial diversity and functional potential of prokaryotic community associated with zoanthid, Palythoa sp

Marine organisms are a valuable source of structurally diverse and bioactive marine natural products (MNPs). Symbiotic associations between microbes and higher marine life forms have become a major focus in MNP research, with growing interest in bioprospecting sessile invertebrates and their microbial communities. This study investigates the prokaryotic community of the least explored colonial cnidarian, Palythoa sp. (family Zoanthidae). An amplicon-based metagenomic analysis revealed a taxonomically diverse community of bacteria and archaea, predominantly comprising Firmicutes, Proteobacteria, Bacteroidota, and Actinobacteria, phyla known for their prolific production of antimicrobial secondary metabolites. Culture-dependent methods using Zobell’s marine agar led to the isolation of Micrococcus luteus and Stenotrophomonas maltophilia. Ethyl acetate extracts of their cell-free supernatants, tested via the agar well diffusion method, have shown antimicrobial activity by inhibiting major aquaculture pathogens viz. Edwardsiella tarda, Aeromonas hydrophila, and Streptococcus agalactiae. Molecular screening detected polyketide synthase-I (PKS-I) genes in both isolates, while non-ribosomal peptide synthetase (NRPS) genes were absent. Further investigation of these microbial isolates and their bioactive compounds holds promise for developing sustainable solutions to disease management in aquaculture, particularly in light of the increasing frequency of disease outbreaks in the industry.