Effect of oxygen mass transfer on the kinetics of Baeyer-Villiger oxidation using a recombinant whole-cell biocatalyst

Performance of resting cells of Escherichia coli expressing cyclohexanone monooxygenase was investigated in a Baeyer-Villiger (BV) oxidation. The impact of oxygen mass transfer on bicyclic lactone production and oxygen metabolic consumption was examined at varying biocatalyst and bicyclic ketone concentrations. Initial rate measurements were conducted with oxygen mass transfer coefficient (kLa) ranging from 19 h-1 to 83 h-1. Results varied notably depending on the initial bicyclic ketone concentration. Below 4 g/L, BV oxidation followed zero-order kinetics for the ketone and oxygen. Intrinsic specific rates for bicyclic lactone production and metabolic oxygen consumption were 1.4 mmol/g/h and 1.7 mmol/g/h, respectively. Mass transfer limitations intensified with higher biocatalyst concentrations and lower kLa-values. A refined conceptual model of oxygen demand for metabolism and BV oxidation was proposed. Above 4 g/L, substrate inhibition of BV oxidation was evident, while metabolic oxygen consumption was less affected. Bicyclic ketone consumption rates indicated intracellular ketone accumulation.