A new [beta]-galactosidase extracted from the infant feces with high hydrolytic and transgalactosylation activity

A [beta]-galactosidase ([beta]-Gal.sub.INF) was directly isolated from feces of an 8-month-old infant. Mass spectrum analysis showed [beta]-Gal.sub.INF with coverage over 50% to the [beta]-galactosidase from Bifidobacterium longum EK3. Accordingly, the [beta]-gal.sub.INF was amplified from the feces metagenomic DNA by degenerate primers. After overexpressed in Escherichia coli, the [beta]-Gal.sub.INF was purified and biochemical characterized. [beta]-Gal.sub.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.sub.m and V.sub.max values for oNPG and lactose were 20.95 ± 2.76 mM, 5004.50 ± 318.8 [mu]mol min.sup.-1 mg.sup.-1 and 140.2 ± 17.7 mM, 293.1 ± 14.7 [mu]mol min.sup.-1 mg.sup.-1, respectively. The production rate of galacto-oligosaccharides by [beta]-Gal.sub.INF from 20% lactose at 50 °C was 33.4 ± 0.67%. These results suggested the [beta]-Gal.sub.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.