Bioprocess design for selective enhancement of fengycin production by a marine isolate Bacillus megaterium

•Agitation rate, medium and inoculum volumes influenced lipopeptide (LP) production.•RSM optimization improved the LP concentration to 5.34 g L−1 in shake flasks.•Oxygen limiting conditions favored fengycin synthesis.•Relatively higher oxygen transfer condition favored surfactin synthesis.•Submerged aeration followed by surface aeration yielded more LP in bioreactor.

Microbial lipopeptide synthesis is often associated with the co-production of more than one family of isoforms. The selective lipopeptide production is strongly influenced by the processing conditions and the limiting nutrient sources such as oxygen and nitrogen during a fermentation process. In the current study, comprehensive investigations carried out in shake flasks revealed that the oxygen-limiting conditions increased the selective fengycin production. The optimal conditions of shake flasks studies of 340 mL medium volume (in 1 L conical flask), 4.67% v/v inoculum volume and 121 rpm agitation speed resulted in a total lipopeptide concentration of 5.34 ± 0.1 g L−1, with more selectivity toward fengycin of 74.1%. Among the three rational approaches investigated to recreate these optimal conditions in a 3.7 L stirred tank bioreactor, the strategy, submerged aeration followed by surface aeration effectively reproduced the optimal conditions of shaker flasks resulting in a total lipopeptide concentration of 4.94 ± 0.15 g L−1, with fengycin selectivity of 71%. The present study thus offers a process design strategy of potential industrial significance to the challenge of selectively enhancing the target product, while marginalizing other closely related co-products.