In Vivo Roles of Fatty Acid Biosynthesis Enzymes in Biosynthesis of Biotin and α-Lipoic Acid in Corynebacterium glutamicum

For fatty acid biosynthesis,Corynebacterium glutamicum uses two type I fatty acid synthases (FAS-I), FasA and FasB, in addition to acetyl-coenzyme A (CoA) carboxylase (ACC) consisting of AccBC, AccD1, and AccE. Thein vivo roles of the enzymes in supplying precursors for biotin and α-lipoic acid remain unclear. Here, we report genetic evidence demonstrating that the biosynthesis of these cofactors is linked to fatty acid biosynthesis through the FAS-I pathway. For this study, we used wild-typeC. glutamicum and its derived biotin vitamer producer BFI-5, which was engineered to expressEscherichia coli bioBF andBacillus subtilis bioI . Disruption of eitherfasA orfasB in strain BFI-5 led to decreased production of biotin vitamers, whereas its amplification contributed to increased production, with a larger impact offasA in both cases. Double disruptions offasA andfasB resulted in no biotin vitamer production. Theacc genes showed a positive effect on production when amplified simultaneously. Augmented fatty acid biosynthesis was also reflected in pimelic acid production when carbon flow was blocked at the BioF reaction. These results indicate that carbon flow down the FAS-I pathway is destined for channeling into the biotin biosynthesis pathway, and that FasA in particular has a significant impact on precursor supply. In contrast,fasB disruption resulted in auxotrophy for lipoic acid or its precursor octanoic acid in both wild-type and BFI-5 strains. The phenotypes were fully complemented by plasmid-mediated expression offasB but notfasA . These results reveal that FasB plays a specific physiological role in lipoic acid biosynthesis inC. glutamicum .IMPORTANCE For thede novo biosynthesis of fatty acids,C. glutamicum exceptionally uses a eukaryotic multifunctional type I fatty acid synthase (FAS-I) system comprising FasA and FasB, in contrast to most bacteria, such asE. coli andB. subtilis , which use an individual nonaggregating type II fatty acid synthase (FAS-II) system. In this study, we reported genetic evidence demonstrating that the FAS-I system is the source of the biotin precursorin vivo in the engineered biotin-prototrophicC. glutamicum strain. This study also uncovered the important physiological role of FasB in lipoic acid biosynthesis. Here, we present an FAS-I enzyme that functions in supplying the lipoic acid precursor, although its biosynthesis has been believed to exclusively depend on FAS-II in organisms. The findings obtained here provide new insights into the metabolic engineering of this industrially important microorganism to produce these compounds effectively.