| Summary: | In nature, aldehyde dehydrogenase (ALDH) is widely distributed and mainly involved in the oxidation of aldehydes. Thermostability is one of the key features for industrial enzymes. The ability of enzymes to withstand a high operating temperature offers many advantages, including enhancing productivity in industries. This study was conducted to understand the structural and biochemical features of ALDH from thermophilic bacterium, <i>Anoxybacillus geothermalis</i> strain D9. The 3D structure of <i>A. geothermalis</i> ALDH was predicted by YASARA software and composed of 24.3% β-sheet located at the center core region. The gene, which encodes 504 amino acids with a molecular weight of ~56 kDa, was cloned into pET51b(+) and expressed in <i>E.coli</i> Transetta (DE3). The purified <i>A. geothermalis</i> ALDH showed remarkable thermostability with optimum temperature at 60 °C and stable at 70 °C for 1 h. The melting point of the <i>A. geothermalis</i> ALDH is at 65.9 °C. Metal ions such as Fe<sup>3+</sup> ions inhibited the enzyme activity, while Li<sup>+</sup> and Mg<sup>2+</sup> enhanced by 38.83% and 105.83%, respectively. Additionally, this enzyme showed tolerance to most non-polar organic solvents tested (xylene, n-dedocane, n-tetradecane, n-hexadecane) in a concentration of 25% <i>v</i>/<i>v</i>. These findings have generally improved the understanding of thermostable <i>A. geothermalis</i> ALDH so it can be widely used in the industry.
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