Influence of Six Carbon Sources with Yeast Extract on Antimicrobial Metabolite Production by Bacterium Associated with Entomopathogenic Nematode

A specific symbiotic Bacillus species isolated from a rhabditid entomopathogenic nematode, Rhabditis (Oscheius) sp. was found to produce a number of bioactive compounds. The present study was conducted to determine the effect of six different carbon sources in combination with yeast extract on the production of antimicrobial substances by Bacillus sp. The yield of crude antimicrobial substances and antimicrobial activity against the test microorganism also differed significantly when the carbon sources in the fermentation media were changed. The highest yield was recorded for maltose plus yeast extract (836 mg/L). The antimicrobial activity was significantly higher in yeast extract plus fructose [Pencillium expansum (46.5 ± 2.12 mm) and Escherichia coli (42.00 mm)] than yeast extract plus other carbon souces used in the study. Antimicrobial activity was significantly reduced in yeast extract plus glucose. HPLC analysis of the crude antimicrobial substances revealed different peaks with different retention times indicating that they produced different compounds. When a carbon source was not included in the fermentation media, the antimicrobial production was substantially reduced to almost eight times. Carbon source in the fermentation medium plays a vital role in the production of antimicrobial substances. Yeast extract and fructose as nitrogen and carbon sources in the fermentation medium produced maximum antimicrobial activity.