Antifungal Potential of Marine Sponge Extract against Plant and Fish Pathogenic Fungi.

The need for discovery of new antibiotics is imperative because previous evidence suggest that development of
resistance to any new antimicrobial agents is inevitable. In addition, compounds not tested for antimicrobial activity also
gives ample scope for rediscovering compounds with antimicrobial activity. This study screens extracts (Diethyl Ether
and Butanol) of a marine red-Sea sponge Negombata magnifica for invitro fungicidal activity against 10 plant and 3 fish
pathogens. Fungicidal activity of the crude diethylether fraction of the sponge against test strains showed exceptionally
high activity against three virulent fish pathogens Exophiala salmonis, Branchiomyces demigrans and Saprolegnia sp.
Furthermore, Minimal Inhibitory Concentration (MIC) of the compound was evaluated with respect to Exophiala salmonis
(1.5 ?g/ml) Branchiomyces demigrans (0.75 ?g/ml) and Saprolegnia sp (3 ?g/ml) respectively. Finally, bioassay guided
isolation and purification led to the identification of the active compound as latrunculin B on the basis of spectroscopic
data. This finding suggests that latrunculin B, could be considered as a lead molecule for the design of new antifungals
for managing common fungal diseases in aquaculture. Toxicity testing of this compound on shrimps indicated that the
compound was non toxic up to a concentration as high as 5 mg/ml suggesting its suitability for use in aquaculture.