Antimicrobial activity of Red Sea corals
Scleractinian corals and alcyonacean soft corals are the two most dominant groups of benthic marine organisms inhabiting the coral reefs of the Gulf of Eilat, northern Red Sea. Antimicrobial assays performed with extracts of six dominant Red Sea stony corals and six dominant soft corals against marine bacteria isolated from the seawater surrounding the corals revealed considerable variability in antimicrobial activity. The results demonstrated that, while the majority (83%) of Red Sea alcyonacean soft corals exhibited appreciable antimicrobial activity against marine bacteria isolated from the seawater surrounding the corals, the stony corals had little or no antimicrobial activity. From the active soft coral species examined, Xenia macrospiculata exhibited the highest and most potent antimicrobial activity. Bioassay-directed fractionation indicated that the antimicrobial activity was due to the presence of a range of compounds of different polarities. One of these antibiotic compounds was isolated and identified as desoxyhavannahine, with a minimum inhibitory concentration (MIC) of 48 μg ml−1 against a marine bacterium. The results of the current study suggest that soft and hard corals have developed different means to combat potential microbial infections. Alcyonacean soft corals use chemical defense through the production of antibiotic compounds to combat microbial attack, whereas stony corals seem to rely on other means.
KeywordsMinimum Inhibitory Concentration Soft Coral Scleractinian Coral Antimicrobial Assay Black Band Disease
We thank the staff of the Inter University Institute of Marine Biology at Eilat for their hospitality and facilities. We thank A. Rudi for the NMR work, A. Price, R. Gottlieb, N. Avni, and A. Gottlieb for their laboratory assistance, and I. Brickner for the coral identification and assistance with the image analysis software. The suggestions of two anonymous reviewers significantly improved the quality of the manuscript. This research was supported by a grant from Israel Ministry of Science and Technology. The corals used in the current study were collected under permission from Israel Nature and National Parks Protection Authority.
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