Characterization of a broad-range aldehyde dehydrogenase involved in alkane degradation in Geobacillus thermodenitrificans NG80-2

SummaryAn aldehyde dehydrogenase (ALDH) involved in alkane degradation in crude oil-degrading Geobacillus thermodenitrificans NG80-2 was characterized in vitro. The ALDH was expressed heterologously in Escherichia coli and purified as a His-tagged homotetrameric protein with a subunit of 57 kDa based on SDS-PAGE and Native-PAGE analysis. The purified ALDH-oxidized alkyl aldehydes ranging from formaldehyde (C1) to eicosanoic aldehyde (C20) with the highest activity on C1. It also oxidized several aromatic aldehydes including benzaldehyde, phenylacetaldehyde, o-chloro-benzaldehyde and o-phthalaldehyde. The ALDH uses only NAD+ as the cofactor, and has no reductive activity on acetate or hexadecanoic acid. Therefore, it is an irreversible NAD+-dependent aldehyde dehydrogenase. Kinetic parameters, temperature and pH optimum of the enzyme, and effects of metal ions, EDTA and Triton X-100 on the enzyme activity were investigated. Physiological roles of the ALDH for the survival of NG80-2 in oil reservoirs are discussed.