Influence of six nitrogen sources with fructose on antimicrobial metabolite production by bacterium associated with entomopathogenic nematode

Abstract

Objective: 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 nitrogen sources in combination with fructose on the production of antimicrobial substances by Bacillus sp. Methods: Bacterial fermentation was carried out using fructose as carbon source and six nitrogen sources (meat peptone, beef extract, yeast extract, tryptone, meat infusion extract and malt extract). Antibacterial activity of the crude extract was studied using disc diffusion assay. The component present in crude extract was studied using analytical HPLC. Results: The yield of crude antimicrobial substances and antimicrobial activity against the test microorganism also differed significantly when the nitrogen sources in the fermentation media were changed. The highest yield was recorded for beef extract plus fructose (921 mg/L). The antimicrobial activity was significantly higher in yeast extract plus fructose [Penicillium expansum (46.5 ± 2.12 mm) and Escherichia coli (42.00 mm)] than yeast extract plus other carbon sources 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. Conclusion: 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