Characterization of a thermostable recombinant β-galactosidase from a thermophilic anaerobic bacterial consortium YTY-70

Abstract

In the present study, a thermophilic anaerobic bacterial consortium YTY-70 that produced thermostable β-galactosidase was isolated from a hot spring in Yongtai (Fujian, China). Based on 16S rRNA sequences, we concluded that Caldicellulosiruptor was the predominant genus in the studied bacterial consortium. Subsequently, a thermostable β-galactosidase gene was cloned and expressed in Escherichia coli as a fusion protein with glutathione S-transferase. The recombinant enzyme exhibited a maximum activity at an optimum pH of 7.0 and an optimum temperature of 75 °C. It had a high activity across a broad pH range (between pH 5.0 and pH 9.0) and high thermal stability at temperatures up to 90 °C. The activity of the recombinant β-galactosidase was enhanced by TritonX-100, Tween-20 and 1 mmol/L 2-mercaptoethanol, while it was inhibited by ethylenediaminetetraacetic acid, sodium dodecyl sulphate, phenylmethylsulphonyl fluoride and 10 mmol/L 2-Me. The enzyme's catalytic function was enhanced by the following metal ions: Na+, K+, Mg2+, Ba2+, Ca2+, Fe2+, Zn2+, Mn2+, Al3+, Cu2+, Fe3+ and Li+. The thermostable β-galactosidase might be a promising candidate for use in food industries, particularly for the dairy industry and biosynthesis of galacto-oligosaccharides, due to its high thermostability and broad pH range.