Isolation of marine bacteria with antimicrobial activities from cultured and field-collected soft corals

Bacteria associated with eight field-collected and five cultured soft corals of Briareum sp., Sinularia sp., Sarcophyton sp., Nephtheidae sp., and Lobophytum sp. were screened for their abilities in producing antimicrobial metabolites. Field-collected coral samples were collected from Nanwan Bay in southern Taiwan. Cultured corals were collected from the cultivating tank at National Museum of Marine Biology and Aquarium. A total of 1,526 and 1,138 culturable, heterotrophic bacteria were isolated from wild and cultured corals, respectively; seawater requirement and antimicrobial activity were then assessed. There is no significant difference between the ratio of seawater-requiring bacteria on the wild and cultured corals. The ratio of antibiotic-producing bacteria within the seawater-requiring bacteria did not differ between the corals. Nineteen bacterial strains that showed high antimicrobial activity were selected for 16S rDNA sequencing. Three strains could be assigned at the family level (Rhodobacteraceae). The remaining 16 strains belong to eight genera: Marinobacterium (2 strains), Pseudoalteromonas (1), Vibrio (5), Enterovibrio (1), Tateyamaria (1), Labrenzia (2), and Pseudovibrio (4). The crude extract from bacteria strains CGH2XX was found to have high cytotoxicity against the cancer cell line HL-60 (IC(50) = 0.94 μg/ml) and CCRF-CEM (IC(50) = 1.19 μg/ml). Our results demonstrate that the marine bacteria from corals have great potential in the discovery of useful medical molecules.