Production and Deactivation of Biosurfactant by Bacillus licheniformis JF‐2

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Abstract
Bacillus licheniformis JF‐2 produces a lipopeptide surfactant with excellent interfacial properties (Lin et al., 1990, 1992). An HPLC assay was developed to monitor the concentration of the lipopeptide in the fermentation broth and was employed to determine the effect of the composition of the growth medium on biosurfactant production. A maximum concentration of 110 mg/L lipopeptide was obtained in optimized media with 1.0% (w/v) glucose as the carbon source. The maximum amount of surfactant was obtained in early stationary‐phase cultures, but subsequently decreased rapidly and disappeared completely from the fermentation broth within 8 h. It was shown that the surfactant is chemically stable in the culture supernatant but becomes internalized by stationary‐phase cells. The apparent rate of surfactant internalization was not inhibited by carbonyl cyanide (m‐chlorophenyl) hydrazone (CCCP), an uncoupler of oxidative phosphorylation, suggesting that it is not dependent on the availability of ATP and/or a charged membrane. A variety of physical and chemical treatments failed to release the surfactant from the cells. In minimal media the rate of surfactant internalization could be reduced by optimizing the concentration of phosphate and by increasing the amount of magnesium, whereas the nitrogen source, calcium, and trace salts had no effect. Since a related lipopeptide has been shown to be responsible for DNA transformation competence in certain Bacillus subtilis strains, it is possible that the internalization of the B. licheniformis JF‐2 surfactant may be a developmentally important process related to the ability of the cells to take up extraneous DNA.