Characterization of a halotolerant GH2 family β-galactosidase GalM from Microvirga sp. strain MC18

Abstract

A new glycoside hydrolase family 2 (GH2) β-galactosidase encoding gene galM was cloned from Microvirga sp. strain MC18 and overexpressed in Escherichia coli. The recombinant β-galactosidase GalM showed optimal activity at pH 7.0 and 50 °C, with a stability at pH 6.0–9.0 and 20–40 °C, which are conditions suitable for the diary environment. The Km and Vmax values for o-nitrophenyl-β-d-galactopyranoside (oNPG) were 1.30 mmol/L and 15.974 μmol/(min·mg), respectively. GalM showed low product inhibition by galactose with a Ki of 73.18 mM and high tolerance for glucose that 86.5% activity retained in the presence of 500 mM glucose. It was also stable and active in 20% of methanol, ethanol and isopropanol. In addition, the enzyme activity of GalM was activated significantly over 0–2 mol/L NaCl (1.6–4.3 fold). These favorable properties make GalM a potential candidate for the industrial application.