Quinone-dependent D-lactate dehydrogenase Dld (Cg1027) is essential for growth of Corynebacterium glutamicum on D-lactate

Here, the gene cg1027 was shown to encode the quinone-dependent D-lactate dehydrogenase (Dld) by enzymatic analysis of the protein purified from recombinant E. coli. The absorption spectrum of purified Dld indicated the presence of FAD as bound cofactor. Inactivation of dld resulted in the loss of the ability to grow with D-lactate, which could be restored by plasmid-borne expression of dld. Heterologous expression of dld from C. glutamicum ATCC 13032 in C. efficiens enabled this species to grow with D-lactate as sole carbon source. Homologs of dld of C. glutamicum ATCC 13032 are not encoded in the sequenced genomes of other corynebacteria and mycobacteria. However, the dld locus of C. glutamicum ATCC 13032 shares 2367 bp of 2372 bp identical nucleotides with the dld locus of Propionibacterium freudenreichii subsp. shermanii, a bacterium used in Swiss-type cheese making. Both loci are flanked by insertion sequences of the same family suggesting a possible event of horizontal gene transfer.Cg1067 encodes quinone-dependent D-lactate dehydrogenase Dld of Corynebacterium glutamicum. Dld is essential for growth with D-lactate as sole carbon source. The genomic region of dld likely has been acquired by horizontal gene transfer.Lactate is a major product of anaerobic metabolism. D-, L, and DL-lactic acid can be utilized by anaerobic and aerobic microorganisms as a carbon and energy source. Propionibacteria preferentially ferment L-lactate to propionate, acetate and carbon dioxide [1], Eubacterium hallii ferments both lactate isomers to butyrate in the human colon [2], while D-lactate is fermented to acetate by sulfate-reducing bacteria such as Desulfovibrio vulgaris [3], or to butyrate by e.g. Clostridium indolis-related strains isolated from human feces [2]. D-lactic acidosis in humans, which can lead to neurotoxicity and cardiac arythmia, is associated with an imbalance of production and degradation of D-lactate by the colonic microbiome [4]. D-lactate oxidizing enzymes