Isolation and identification of a Microbacterium sp. LW106 strain producing cold-active β-galactosidase, and study on its enzyme production conditions and enzymatic properties

Abstract:

[Background] Cold-active β-galactosidases are typically characterized by a high lactose hydrolysis activity at low temperature. Such a characteristic makes cold-active β-galactosidase highly attractive for application in low-lactose milk production industry, and how to mine novel cold-active β-galactosidase with enzymatic properties perfectly suitable for lactose hydrolysis in milk solution condition becomes a research focus. [Objective] This study is aiming to screen novel strains producing cold-active β-galactosidase from glacier sediments at China No.1 glacier in Tianshan Mountains and to evaluate if the enzymatic properties of the cold-active β-galactosidase is suitable for further application in low-lactose milk production. [Methods] Primary screening using X-gal culture plate, and secondary screening by assaying the relative β-galactosidase activity at low temperature were carried out. The target strain selected was identified by physiological, biochemical and 16S rRNA gene sequencing. The growth condition and enzyme production condition of the isolate were optimized by single-factor experiment. Enzymatic properties of the partially purified β-galactosidase produced by the isolate were also investigated. [Results] LW106, a strain with high β-galactosidase activity, was identified as Microbacterium sp. LW106. The optimal temperature for LW106 producing β-galactosidase is 25 °C. Soluble starch was the optimal carbon source for LW106 to produce β-galactosidase, the optimum medium initial pH was 7.0, and the optimal inoculum size was 3%. Preliminary study on its enzymatic properties showed that the optimal pH of the β-galactosidase of strain LW106 was 6.0, and the optimal reaction temperature was 35 °C with a relative activity of 78% at 4 °C. The β-galactosidase produced by LW106 showed the best stability at 4 °C and pH 7.0. Metal ion Na+ at a level of 10 mmol/L did not inhibit the activity of β-galactosidase of LW106, while 10 mmol/L of Ca2+ activated the β-galactosidase activity. [Conclusion] The enzymatic properties of β-galactosidase produced by Microbacterium sp. LW106 indicated it may be suitable for lactose hydrolysis at low temperature, showing good application potential in low-lactose milk production industry.