Antagonistic effect of marine Nocardia brasiliensis against the fish pathogen Vibrio damsela: Application of Plackett- Burman experimental design to evaluate factors affecting the production of the antibacterial agent

Sixteen actinomycete strains were tested for their potentiality to produce bioactive compounds that inhibit the growth of the fish pathogen Vibrio damsela. A marine strain identified as Nocardia brasiliensis produced a compound that showed the largest inhibition zone and highest activity against the tested organism. High level of MgSO₄7H₂O and low levels of all other components in the culture medium supported the production of the antagonistic compound as evaluated by the application of Plackett- Burman experimental design. Cultures adjusted to pH 8, incubated at 40°C under static condition lead to higher production of the antagonistic compound. Antagonistic activity of the compound produced from the optimized culture conditions against Vibrio damsela, showed 2.9 fold increase than that obtained from the basal medium. The inhibitory substance was found to be a low molecular weight compound, heat stable and resistant to proteolytic enzymes.