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.