Beta-galactosidase activity in psychrotrophic microorganisms and their potential use in food industry

Twenty-one psychrotrophic resp. psychrophilic bacterial strains were screened for presence of b-galactosidase activity which showed 8 of them. b-Galactosidase activity of these strains was determined for 2 substrates – synthetic substrate (ONPG) and lactose – and also temperature profile of this enzyme was measured. b-Galactosidase from Arthrobacter sp. C2-2 not only proved the typical properties of cold-active enzyme, but it also preferred lactose as a substrate. Therefore, it was chosen for further isolation and purification and was found that it contains two b-galactosidase isoenzymes. One of them had strong preference for lactose and was able to catalyse transglycosylation reactions at low temperature. It has, thus, potential use in food technology.  

Biochemical and Phylogenetic Analyses of a Cold-Active β-Galactosidase from the Lactic Acid Bacterium Carnobacterium piscicola BA

ABSTRACT We are investigating glycosyl hydrolases from new psychrophilic isolates to examine the adaptations of enzymes to low temperatures. A β-galactosidase from isolate BA, which we have classified as a strain of the lactic acid bacterium Carnobacterium piscicola, was capable of hydrolyzing the chromogen 5-bromo-4-chloro-3-indolyl β-d-galactopyranoside (X-Gal) at 4°C and possessed higher activity in crude cell lysates at 25 than at 37°C. Sequence analysis of a cloned DNA fragment encoding this activity revealed a gene cluster containing three glycosyl hydrolases with homology to an α-galactosidase and two β-galactosidases. The larger of the two β-galactosidase genes, bgaB, encoded the 76.8-kDa cold-active enzyme. This gene was homologous to family 42 glycosyl hydrolases, a group which contains several thermophilic enzymes but none from lactic acid bacteria. The bgaB gene from isolate BA was subcloned in Escherichia coli, and its enzyme, BgaB, was purified. The purified enzyme was highly unstable and required 10% glycerol to maintain activity. Its optimal temperature for activity was 30°C, and it was inactivated at 40°C in 10 min. TheKm of freshly purified enzyme at 30°C was 1.7 mM, and the V max was 450 μmol · min−1 · mg−1 with o-nitrophenyl β-d-galactopyranoside. This cold-active enzyme is interesting because it is homologous to a thermophilic enzyme fromBacillus stearothermophilus, and comparisons could provide information about structural features important for activity at low temperatures.