A new β-galactosidase extracted from the infant feces with high hydrolytic and transgalactosylation activity

A beta-galactosidase (beta-Gal(INF)) was directly isolated from feces of an 8-month-old infant. Mass spectrum analysis showed beta-Gal(INF) with coverage over 50% to the beta-galactosidase from Bifidobacterium longum EK3. Accordingly, the beta-gal(INF) was amplified from the feces metagenomic DNA by degenerate primers. After overexpressed in Escherichia coli, the beta-Gal(INF) was purified and biochemical characterized. beta-Gal(INF) existed as homotetramer and homodimer, whose activity (optimal at 50 degrees C, pH 6.5) was exhilaratingly increased to 484% by artificial intestinal juice. The K-m and V-max values for oNPG and lactose were 20.95 +/- 2.76 mM, 5004.50 +/- 318.8 mu mol min(-1) mg(-1) and 140.2 +/- 17.7 mM, 293.1 +/- 14.7 mu mol min(-1) mg(-1), respectively. The production rate of galacto-oligosaccharides by beta-Gal(INF) from 20% lactose at 50 degrees C was 33.4 +/- 0.67%. These results suggested the beta-Gal(INF) with high hydrolytic and transgalactosylation activity from the infant intestinal has great potential as infant lactase preparation. Moreover, this study provided a new way for exploring undetected enzymes by uncultured-dependent methods.