Identification and characterization of aldehyde-producing acyl-CoA reductase derived from <i>Klebsiella pneumoniae</i>

Medium-chain aldehydes are important precursors of alkanes, which could be used as a biofuel. In this study, we screened 1300 microorganisms-including bacteria (including actinomycetes), yeasts, molds, and basidiomycetes-for their ability to produce tetradecanal from tetradecanoic acid. Among these microorganisms, Klebsiella pneumoniae subsp. pneumoniae NBRC3321 exhibited the highest 1-tetradecanol-producing activity from tetradecanoic acid. This strain was therefore selected as a suitable candidate for aldehyde-producing enzyme analysis. A novel aldehyde-producing acyl-CoA reductase gene (acrI) was isolated from K. pneumoniae subsp. pneumoniae NBRC3321, which comprises 1404 bp encoding a polypeptide of 49.1 kDa. His6-tagged AcrI requires NADH as a coenzyme to convert tetradecanoyl-CoA into tetradecanal. The enzyme catalyzed both acyl-CoA reduction and aldehyde hydrogenation, producing alcohol with acyl-CoA substrates of C6-C12, whereas it catalyzed acyl-CoA reduction producing only aldehydes with acyl-CoA substrates of C14-C16.