Lactobacillus reuteri NAD(P)H oxidase: Properties and coexpression with propanediol-utilization enzymes for enhancing 3-hydroxypropionic acid production from 3-hydroxypropionaldehyde

Lactobacillus reuteri metabolizes glycerol through propanediol-utilization (Pdu) pathway to 1,3-propanediol (1,3-PD) via 3-hydroxypropionaldehyde (3-HPA) as intermediate. In the resting cells, the oxidized co-factor obtained in the reaction is regenerated by simultaneous oxidation of 3-HPA to 3-hydroxypropionic acid (3-HP) using propionaldehyde dehydrogenase (PduP), phosphotransacylase (PduL) and propionate kinase (PduW). We have earlier shown that the use of resting cells of recombinant Escherichia coli expressing the oxidative pathway gives the highest theoretical yield of 1 mol 3-HP per mol 3-HPA but is limited by cofactor depletion. In the present study, the gene encoding the enzyme NAD(P)H oxidase (LreuNox) that utilizes molecular oxygen as substrate, was isolated from L. reuteri and heterologously overexpressed in E. coli. LreuNox has a pH optimum of 6 and exhibits V_max of 101.1 ± 2.2 U/mg with NADH, which is 30% higher than that for NADPH. Co-expression of LreuNox with PduP, PduL and PduW in E. coli enhances the biocatalytic lifetime as well as productivity at least two-fold compared to that achieved without co-factor regeneration.