Antibacterial and repellent activities of marine bacteria associated with algal surfaces

Despite the ubiquity of bacteria in the marine environment little is known about the structure and function of microbial communities associated with marine macroorganisms. Using a range of traditional and novel culture methods, 280 isolates of epiphytic marine bacteria from a range of marine algae were obtained in pure culture. Sixty of the 280 isolates (21%) exhibited antibiotic activity against a test battery of fouling bacteria. Fractionation of the culture supernatants derived from two strains, GB3 and AR55, indicated the presence of a multicomponent defence system consisting of both organic and water soluble components. In addition, eight out of 21 strains (38%) screened using a spectrophotometric chemotaxis assay, produced metabolites capable of eliciting a negative chemotactic response in a motile fouling bacterium. A significant fraction of these isolates therefore have the potential to control the microbial population on the seaweed surface, either through inhibiting the growth, or influencing the tactic behaviour of potentially competing bacteria.