Enhanced biosurfactant production by a Bacillus licheniformis mutant

A Bacillus licheniformis mutant derived by random mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine treatment producing high levels of the lipopeptide biosurfactants was selected by an ion-pair plate assay. The mutant, designated B. licheniformis KGL11, is capable of producing lipopeptide biosurfactants at concentrations lip to 391 mg l(-1) which is twelve rimes more than the parent strain. HPLC analysis, infrared spectroscopy analysis, and surface tension measurement indicated that the biosurfactants produced by the mutant were identical to those produced by the wildtype strain. The biosurfactants exhibited a low surface tension of 26.5 dyne cm(-1) and a low critical micelle concentration of 10 mg l(-1). Similar to the wildtype strain, the mutant produced biosurfactants at the mid-exponential phase and subsequently deactivated biosurfactants at the onset of the stationary phase; nevertheless, the deactivated biosurfactants was re-excreted into the culture upon further incubation. (C) 1998 Elsevier Science Inc.