Scalable catalyst production process for oleate hydratase whole-cell biocatalysis

The sustainable production of hydroxy fatty acids, such as 10-hydroxystearic acid (10-HSA), by biocatalysis is a promising alternative to petrochemical and castor oil-derived products. However, industrial implementation still requires an efficient and scalable process for biocatalyst production by fermentation, which precedes the biotransformation to 10-HSA. In general, industrial biocatalysis is commonly performed using whole cells, which are cheaper than purified enzymes. Still, the fermentation process itself is a major cost contributor requiring a high-yielding and scalable process. Here, we established and scaled a lactose-induced fed-batch process to produce an Escherichia coli BL21 (DE3) based whole-cell biocatalyst containing an oleate hydratase from Stenotrophomonas nitritireducens. The two-phased process employs an initial growth phase on glucose, followed by an induced feed phase using glycerol and lactose. When comparing two different growth rates during enzyme expression, a higher growth rate was found beneficial, resulting in a higher biomass concentration of 69.2 ± 0.5 g L^-1 and a yield increase of 80 % while maintaining biocatalyst activity at >85 % conversion. This highlights the importance of process design variables, such as growth rate settings, for a high-yielding and economic process. Feasibility of the process was demonstrated by scaling into a 150 L bioreactor, achieving a biomass concentration of 60.6 ± 0.4 g L^-1 with a yield of 0.44 g_C,Biomass g_C ^-1 and 91.5 ± 1.4 % conversion. Supplemented with an initial test of suitable unit operations for technical biomass separation, this work provides a fermentation route for a whole-cell oleate hydratase biocatalyst, paving the way for further scaling toward industrial 10-HSA production.