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

A β-galactosidase (β-Gal_INF) was directly isolated from feces of an 8-month-old infant. Mass spectrum analysis showed β-Gal_INF with coverage over 50% to the β-galactosidase from Bifidobacterium longum EK3. Accordingly, the β-gal_INF was amplified from the feces metagenomic DNA by degenerate primers. After overexpressed in Escherichia coli, the β-Gal_INF was purified and biochemical characterized. β-Gal_INF existed as homotetramer and homodimer, whose activity (optimal at 50 °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 μmol min^-1 mg^-1 and 140.2 ± 17.7 mM, 293.1 ± 14.7 μmol min^-1 mg^-1, respectively. The production rate of galacto-oligosaccharides by β-Gal_INF from 20% lactose at 50 °C was 33.4 ± 0.67%. These results suggested the β-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.