Identifying membrane-bound quinoprotein glucose dehydrogenase from acetic acid bacteria that produce lactobionic and cellobionic acids.

Abstract

Acetic acid bacteria are used in the commercial production of lactobionic acid (LacA). However, the lactose-oxidizing enzyme of these bacteria remains unidentified. Lactose-oxidizing activity has been detected in bacterial membrane fractions and is strongly inhibited by d-glucose, suggesting that the enzyme was a membrane-bound quinoprotein glucose dehydrogenase, but these dehydrogenases have been reported to be incapable of oxidizing lactose. Thus, we generated m-GDH-overexpressing and -deficient strains of Komagataeibacter medellinensis NBRC3288 and investigated their lactose-oxidizing activities. Whereas the overexpressing variants produced ~2-5-fold higher amounts of LacA than the wild-type strains, the deficient variant produced no LacA or d-gluconic acid. Our results indicate that the lactose-oxidizing enzyme from acetic acid bacteria is membrane-bound quinoprotein glucose dehydrogenase. Abbreviations: LacA: lactobionic acid; AAB: acetic acid bacterium; m-GDH: membrane-bound quinoprotein glucose dehydrogenase; DCIP: 2,6-dichlorophenolindophenol; HPAEC-PAD: high-performance anion-exchange chromatography with pulsed amperometric detection.