Application of Combined Irradiation Mutagenesis Technique for Hyperproduction of Surfactin in Bacillus velezensis Strain AF_3B.

The major challenge in large-scale industrial use of lipopeptide surfactin is the low yield by indigenous bacterial strains and the higher cost of its production that have been proved as a limiting factor in commercial applications. Therefore, there is an urgent demand for high-yielding strains that can be achieved through strain improvement. A first report on the use of a combination of UV and gamma-irradiation mutagenesis for the development of surfactin hyperproducing mutants of Bacillus spp. proved to be significant and resulted in a twofold enhancement in surfactin yield. The mutant was able to grow and produce surfactin on all the tested carbon and nitrogen sources, while 2% glycerol favored maximum surfactin yield (1.62 g/L) as compared to the wild-type strain that showed a maximum 0.85 g/L surfactin yield at 3% sucrose. Additionally, the mutant exhibited a good yield of pure surfactin, that is, 1.55 g/L as compared to the wild strain (0.411 g/L) by using corn steep liquor as the main component of the fermentation medium. The study concluded overall a threefold enhancement in the relative abundance of purified surfactin and its isoforms detected by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis in mutant strain AF-UVγ2500.