Development of foam-free biosurfactant production processes using Bacillus licheniformis

Abstract

Microbial biosurfactants are considered environmentally friendly alternatives to synthetic surfac-tants in numerous applications. One of the main bottlenecks to their widespread use is the lack of effective processes for their production on an industrial scale. Biosurfactant production using conventional aerated bioreactors results in excessive foaming due to the combination of air injec-tion and their tensioactive properties. A not widely explored approach to overcome this problem is the development of foam-free production processes, which require the identification and charac-terization of appropriate microorganisms. Bacillus licheniformis EL3 was evaluated for biosurfac-tant production under oxygen-limiting conditions in a bioreactor, using a mineral medium con-taining glucose as a carbon source and NaNO3 and NH4Cl as nitrogen sources. After optimizing the operational conditions, glucose concentration, and inoculum strategy, B. licheniformis EL3 produced 75 ± 3 mg biosurfactant/L in 43 h. The purified biosurfactant exhibited exceptional sur-face active properties, with minimum surface tension values (29 mN/m) and a critical micelle concentration (27 mg/L) similar to those achieved with commercial surfactin. Furthermore, bio-surfactant yield per substrate (YP/S = 0.007 g biosurfactant/g glucose) was similar to the figures re-ported for Bacillus subtilis strains grown in similar conditions, whereas biosurfactant yield per bi-omass (YP/X = 0.755 g biosurfactant/g biomass) and specific biosurfactant productivity (qBS = 0.018 g biosurfactant/(g biomass × h)) were almost three times higher when compared to previous reports. The results obtained indicate that B. licheniformis EL3 is a promising candidate for the develop-ment of foam-free biosurfactant production processes at an industrial scale.