Enzymes related to β-hydroxyacid dehydrogenases/3-hydroxyisobutyrate dehydrogenases are ubiquitous, but most of them have not been characterized. An uncharacterized protein with moderate sequence similarities to Gluconobacter oxydans succinic semialdehyde reductase and plant glyoxylate reductases/succinic semialdehyde reductases was found in the genome of Acetobacter aceti JCM20276. The corresponding gene was cloned and expressed in Escherichia coli. The gene product was purified and identified as a glyoxylate reductase that exclusively catalyzed the NAD(P)H-dependent reduction of glyoxylate to glycolate. The strict substrate specificity of this enzyme to glyoxylate, the diverged sequence motifs for its binding sites with cofactors and substrates, and its phylogenetic relationship to homologous enzymes suggested that this enzyme represents a novel class of enzymes in the β-hydroxyacid dehydrogenase family. This study may provide an important clue to clarify the metabolism of glyoxylate in bacteria. Abbreviations: GR: glyoxylate reductase; GRHPR: glyoxylate reductase/hydroxypyruvate reductase; HIBADH: 3-hydroxyisobutyrate dehydrogenase; SSA: succinic semialdehyde; SSAR: succinic semialdehyde reductase

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Acetobacter aceti is used in industry to produce vinegar by converting ethanol into acetic acid. We determined the complete genome sequence of A. aceti JCM20276, which is composed of one chromosome and four plasmids. This study may contribute to a better understanding of the genes necessary for acetic acid production.