The Environmental Biotechnology Lab

Living corals are frequently colonized by bacteria that may be pathogenic. One way they are able to combat microbial attack is by chemical defense. This is especially critical for the early developmental stages of the coral. Extracts from various reproductive and developmental stages of the Red Sea soft coral Parerythropodium fulvum fulvum exhibited antimicrobial activity against several co-occurring and potentially pathogenic marine bacteria. High activity was found particularly against Vibrio sp. (strain P-1), isolated from a necrotic coral tissue. However, no antimicrobial activity was observed against the coral-associated bacterial strains isolated from the coral tissue and its mucoid surface. The minimum inhibitory concentration of the coral crude extract against this Vibrio sp. was 1.25 mg ml^-1. Bioassay-guided fractionation of the coral extract indicated that the antimicrobial activity was due to the presence of a range of secondary compounds of different polarities, which were also present in the tissue in trace amounts. The antimicrobial activity was present in all reproductive and developmental stages of the coral against the sensitive bacteria. This study provides the first comprehensive evidence for antimicrobial activity in coral larvae against co-occurring marine bacteria. It is concluded that antimicrobial activity detected in the extracts of P. f. fulvum is specific rather than broad spectrum. This specificity may be important in order to enable certain bacteria to live in close association with their coral host.