IMPROVEMENT OF ANTIMICROBIAL ACTIVITY OF COMPOUNDS PRODUCED BY BACILLUS SP. ASSOCIATED WITH A RHABDITID SP. (ENTOMOPATHOGENIC NEMATODE) BY CHANGING CARBON AND NITROGEN SOURCES IN FERMENTATION MEDIA

Abstract

A specific symbiotic Bacillus sp. isolated from a rhabditid entomopathogenic nematode, Rhabditis (Oscheius) sp. was found to produce a large number of bioactive compounds. The present study was conducted to determine the effect of carbon and nitrogen sources for the production of antimicrobial substances by Bacillus sp. The yield of the crude antimicrobial substances and antimicrobial activity against the test microorganism also differed significantly when carbon and nitrogen sources in the fermentation media were changed. The antimicrobial activity was significantly high in yeast extract plus fructose [Pencillium expansum (46.5±2.12 mm) and Escherichia coli (42±1.41 mm)] and yeast extract plus maltose followed by meat peptone plus fructose. Antimicrobial activity was significantly reduced with malt extract irrespective of its carbon sources. HPLC analysis of the crude antimicrobial substances revealed different peaks with different retention time indicating that they produced different compounds. When the carbon source was not included in the fermentation media, the antimicrobial production was substantially reduced. The results indicate that carbon source in the fermentation media plays a vital role in the production of antimicrobial substances. It is concluded that yeast extract and fructose as nitrogen and carbon sources produced maximum activity.