Analysis of biosurfactants produced by bacteria growing on textile sludge and their toxicity evaluation for environmental application

In the present study two promising bacterial strains were isolated from textile sludge and studied for biosurfactant production. These strains were identified as Stenotrophomonas sp. BAB-6435 and Brevisbacillus brevis BAB-6437. Growth, biosurfactant production and stable emulsification of both bacteria were optimized through response surface methodology using a Box-Behnken design (BBD). The optimum conditions included a pH of 8.5, a temperature of 42 °C and a NaCl concentration of 5 mg 100 mL⁻¹. The biosurfactants produced by Stenotrophomonas sp. BAB-6435 and Brevisbacillus brevis BAB-6437 were purified and characterized by TLC, FTIR, SEM-EDS and GC-MS. The functional biosurfactant molecules were identified as glycolipid (Palmitic acid-Ribo-Gala-Malt) and lipopeptide (Steric acid-Ala-Ala-Gly-Leu-Se-Pro-As) from Stenotrophomonas sp. BAB-6435 and Brevisbacillus brevis BAB-6437, respectively. Both of the biosurfactansts have excellent surface tension reduction abilities at lower critical micelle concentrations (CMCs). Purified biosurfactants also exhibited antimicrobial activity toward pathogenic microbes while they were found to be nontoxic in seed germination tests. The results indicate that the biosurfactants from Stenotrophomonas sp. BAB-6435 and Brevisbacillus brevis BAB-6437 have unique properties including excessive foam-forming, antimicrobial activity and a lack of toxicity, which facilitate their environmental use.