Bacillus licheniformis: the unexplored alternative for the anaerobic production of lipopeptide biosurfactants?

Abstract

Microbial biosurfactants have attracted the attention of researchers and companies for the last decades, as they are considered promising candidates to replace chemical surfactants in numerous applications. Although in the last years, considerable advances were performed regarding strain engineering and the use of low-cost substrates in order to reduce their production costs, one of the main bottlenecks is their production at industrial scale. Conventional aerobic biosurfactant production processes result in excessive foaming, due to the use of high agitation and aeration rates necessary to increase dissolved oxygen concentration to allow microbial growth and biosurfactant production. Different approaches have been studied to overcome this problem, although with limited success. A not widely explored alternative is the development of foam-free processes through the anaerobic growth of biosurfactant-producing microorganisms. Surfactin, produced by Bacillus subtilis, is the most widely studied lipopeptide biosurfactant, and the most powerful biosurfactant known so far. Bacillus licheniformis strains produce lichenysin, a lipopeptide biosurfactant which structure is similar to surfactin. However, despite its extraordinary surface-active properties and potential applications, lichenysin has been scarcely studied. According to previous studies, B. licheniformis is better adapted to anaerobic growth than B. subtilis, and could be a good alternative for the anaerobic production of lipopeptide biosurfactants. In this review, the potential and limitations of surfactin and lichenysin production under anaerobic conditions will be analyzed, and the possibility of implementing foam-free processes for lichenysin production, in order to expand the market and applications of biosurfactants in different fields, will be discussed.