http://aem.asm.org/content/84/13/e00377-18.short

Although some bacteria, including Chromohalobacter salexigens DSM 3043, can use glycine betaine (GB) as a sole source of carbon and energy, little information is available about the genes  and their encoded proteins involved in the initial step of the GB degradation pathway. In the present study, the results of  conserved domain analysis, construction of in-frame deletion mutants, and an in vivo functional complementation assay suggested that the open reading frames Csal_1004 and Csal_1005, designated bmoA and bmoB, respectively, may act as the terminal oxygenase and the ferredoxin reductase genes in a novel Rieske-type oxygenase system  to convert GB to dimethylglycine in C. salexigens DSM 3043. To further verify their function, BmoA and BmoB were heterologously overexpressed in Escherichia coli, and ¹³C nuclear magnetic resonance analysis revealed that dimethylglycine was accumulated in E. coli BL21(DE3) expressing BmoAB or BmoA. In addition, His-tagged BmoA and BmoB were individually purified to electrophoretic homogeneity  and estimated to be a homotrimer and a monomer, respectively. In vitro biochemical analysis indicated that BmoB is an NADH-dependent flavin reductase with one noncovalently bound flavin adenine  dinucleotide (FAD) as its prosthetic group. In the presence of BmoB, NADH, and flavin, BmoA could aerobically degrade GB to  dimethylglycine with the concomitant production of formaldehyde. BmoA exhibited strict substrate specificity for GB, and its  demethylation activity was stimulated by Fe²⁺. Phylogenetic analysis showed that BmoA belongs to group V of the Rieske nonheme iron oxygenase (RO) family, and all the members in this group were able to use quaternary ammonium compounds as substrates.