Heterologous expression of glycoside hydrolase family 2 and 42 β-galactosidases of lactic acid bacteria in Lactococcus lactis

This study characterized a glycoside hydrolase family 42 (GH42) beta-galactosidase of Lactobacillus acidophilus (LacA) and compared lactose hydrolysis, hydrolysis of oNPG, pNPG and pNPG-analogues and galactooligosaccharides (GOSs) formation to GH2 beta-galactosidases of Streptococcus thennophilus (LacZ type), Lactobacillus plantarum and Leuconostoc mesenteroides subsp. cremoris (both LacLM type). Beta-galactosidases were heterologously expressed in Lactococcus lactis using a p170 derived promoter; experiments were performed with L lactis crude cell extract (CCE). The novel GH42 beta-galactosidase of Lb. acidophilus had lower activity on lactose, oNPG and pNPG but higher relative activity on pNP analogues compared to GH2 beta-galactosidases, and did not transgalactosylate at high lactose concentrations. Temperature and pH optima for lactose hydrolysis varied between GH2 beta-galactosidases. oNPG and pNPG were the preferred substrates for hydrolysis; in comparison, activity on pNPG-analogues was less than 1.5%. GH2 beta-galactosidases formed structurally similar GOS with varying preferences. The diversity of lactic acid bacteria beta-galactosidase activity in L. lactis CCE can be exploited in future nutritional or therapeutic applications. (C) 2010 Elsevier GmbH. All rights reserved.