Antibacterial activity of bioactive compounds produced by bacteria associated with hard corals in the Gulf of Aqaba

One of the most important constituents of the marine ecosystem is the coral reefs, where they support many of the surrounding species. In addition, this study investigates the ability of bacteria associated with two hard corals (Galaxea fascicularis and Stylophora pistillata) that have been isolated from the Gulf of Aqaba, Jordan to investigate the production of antibacterial agents. A total of 93 bacterial isolates associated with the aforementioned coral species were isolated from the mucus of these coral species. Mucus-associated bacterial species were identified using 16S rRNA gene sequencing. The main bacterial group was Gammaproteobacteria present at all isolates associated with the two corals which include; Psychrobacter aquaticus, Stenotrophomonas maltophilia, Pseudomonas segetis, Psychrobacter pacificensis, Acinetobacter sp, Bacillus sp, Klebsiella sp, Micrococcus luteus, Mycobacterium sp, Planococcus sp, Providencia sp, Pseudoalteromonas sp, Staphylococcus sp, Streptococcus agalactiae, Vibrio sp, and Uncultured Psychrobacter. Screening of the bacterial isolates revealed that only seven bacterial isolates from mucus were capable of producing an antibacterial compounds. The extracted bioactive substances were further purified using size exclusion chromatography and concentrated by lyophilization. The results indicated that the highest inhibition of the antibacterial activity was achieved by the antibacterial compounds produced by coral mucus associated isolates against Micrococcus luteus ATCC 9341, while the lowest inhibition was against Serratia marcescens ATCC 27117. However, the minimum inhibitory concentration value ranges between 250-600 mg/ml. In conclusion, the corals associated bacteria plays a role in protecting the corals from pathogens which is considered an important source for natural antibacterial compounds.