“…Even the classical Baeyer-Villiger oxidations, in which an ester/lactone is generated from a ketone/cyclic ketone (e.g., transformation of ADD into testolactone, an aromatase inhibitor) (Kołek et al, 2008 ), can be catalyzed by enzymes called Baeyer-Villiger monooxygenases (BVMOs) that use molecular oxygen and NADPH (Figure 4 ; Leisch et al, 2011 ). To perform these chemical functionalizations on steroidal molecules, several wild-type microorganisms that possess the steroid-modifying enzymatic activities of interest are frequently used at an industrial scale (Supplementary Table 2 ; Zhang et al, 1998 ; El-Kadi and Mostafa, 2004 ; Li et al, 2005 , 2017 ; Reese, 2007 ; Roglič et al, 2007 ; Manosroi et al, 2008 ; Yildirim et al, 2010 ; Peart et al, 2011 ; Bhatti and Khera, 2012 ; Donova and Egorova, 2012 ; Prakash and Bajaj, 2017 ). Since these bioconversions often exhibit various drawbacks such as low selectivity and substrate conversion yields, and may even require the culture of opportunistic pathogenic microorganisms (e.g., Rhizopus oryzae ), it has been proposed the design of alternative MCFs by using recombinant DNA technologies in recent years.…”