Isolation of marine fungi Aspergillus sp and its in vitro antifouling activity against marine bacteria

Biofouling is considered as a main issue of concern in aquatic environment causing severe economic loss and pollution. The aim of the present study was to isolate marine fungus antagonistic to biofouling bacteria and to define antifouling compounds present in it. Using standard plate method five predominant biofouling bacteria viz., Methylococcus sp., Flavobacterium sp., Marinococcus sp., Serratia sp. and Pseudomonas sp. were isolated from marine solid substances on Zobell's agar. Tolerance range of these bacteria to NaCl was 2-10%. Isolation of fungi from mangrove and estuarine sediments and their screening identified Aspergillus sp. EF4 as a potential isolate. This isolate caused inhibition of all the five test bacterial cultures measuring zone diameters respectively of 11, 16, 12, 13 and 11mm. Subsequent to submerged fermentation using shaking flask method this fungus produced bioactive compounds within 5 days. The culture parameters optimized were raffinose as carbon source, yeast extract as lone nitrogen source, pH up to 9.0 and temperature up to 40 degrees C. Antifouling compounds of culture filtrate were separated and detected by a three-step procedure involving thin layer chromatography, bioautography and preparative TLC. The in vitro assay involving glass slide wooden stick-biofilm method revealed that these compounds could cause inhibition and destruction of bacteria to an extent of 2.16 x 10(4) CFU ml(-1) and 2.46 x 10(4) CFU ml(-1) respectively while growth of bacteria in control beaker was enumerated to be 4.41 x 10(4) CFU ml(-1). High performance liquid chromatography of culture filtrate indicated probable principal antifouling compound as Fumonisin B2. Isolation of antagonistic marine fungus from Indian coast and detection of its antifouling compound would help in planning effective strategies for controlling biofouling in marine environment.