Production, characterisation and antimicrobial activity of biosurfactants produced by soil bacteria using agricultural wastes

Abstract

In this study we selected eight bacterial strains identified as Bacillus spp., Pseudomonas sp. and Enterobacter sp. Spent coffee grounds, waste frying oil and molasses were used as growth substrates for these bacteria to produce biosurfactants. Emulsification activity of higher than 90% was found in Bacillus spp. and Enterobacter sp. According to the CTAB-methylene blue agar test, most of the biosurfactants obtained were anionic molecules. Furthermore, oil displacement and drop collapse tests showed that biosurfactants produced from waste frying oil and molasses cultures possessed active surface properties. Interfacial activities of biosurfactants significantly increased when waste frying oil was used as a substrate. Biosurfactants were then partially purified for TLC, FTIR and NMR analysis. The results suggested that these bacteria could produce glycolipids and surfactin-like compounds. More importantly, we found from an antimicrobial activity test that these biosurfactants could inhibit a wide range of Gram-negative and Gram-positive bacteria. In particular, biosurfactants produced in this experiment showed strong inhibition effects against pathogens, especially an antibiotic-resistant Serratia marcescens. The zone of inhibition diameter was approximately 10–30mm. Our results highlight the potential use of waste frying oil as a low-cost substrate to produce biosurfactants that could be applied for pharmaceutical purposes.