Coral mucus bacteria as a source for antibacterial activity

In the oligotrophic marine environment there are ecological niches rich in nutrients and diverse in bacterial populations. One such niche is the coral surface mucus layer. Interactions amongst microorganisms found in coral mucus may be symbiotic or competitive; competing over space and food. It has been hypothesized that the microbial communities found on the coral surface may play a role in the coral's defense, possibly through the production of antimicrobial substances. To find potentially active compounds produced by coral-mucus bacteria, over 200 selected microorganisms isolated from the mucus layer of a number of coral species were grown using agar plating technique. Screening for antibacterial substances was performed using overlay and drop techniques, and antibacterial activity was tested against indicator microorganisms. Results indicate that more than 20% of cultivable mucus-associated bacteria originating from hard corals demonstrated antibacterial activity. Isolates obtained from hard corals demonstrated higher percentage of activity than soft corals' isolates. Isolates related to the genera Vibrio and Pseudoalteromonas demonstrated high activity against both gram-positive and gram-negative bacteria. These results demonstrate the existence of microorganisms with antibacterial activity on the coral surface, indicating that they may play a role in protecting the coral host against pathogens.