Beta-galactosidases identifed using metagenomics data from dairy industries stabilization ponds. Beta-galactosidases from dairy industries stabilization ponds

Stabilization ponds are a common treatment technology for wastewater generated by dairy industries. Large proportions of cheese whey are thrown into these ponds, which represents an environmental problem, because of the large volume produced and the high biological and chemical oxygen demands. Due to its composition, mainly lactose and proteins, it can be considered as a raw material for value-added products, through physicochemical or enzymatic treatments.β-galactosidases (EC 3.2.1.23) are lactose modifying enzymes that can transform lactose in free monomers, glucose and galactose, or galactooligosacharides (GOS).Here, we report the identification of novel genes encoding β-galactosidases, identified via whole-genome shotgun sequencing of the metagenome of dairy industries stabilization ponds.The genes were selected based on the conservation of catalytic domains, comparing against the CAZy database, and focusing on families with β-galactosidases activity (GH1, GH2, and GH42) A total of 394 candidate genes were found, all belonging to bacterial species. Twelve candidates were selected for cloning and expression in heterologous systems. Candidate genes were amplified and cloned into plasmid vectors for inducible protein expression. Six putative β-galactosidase proteins were efficiently expressed. Five affinity purified enzymes cleaved efficiently ortho-Nitrophenyl-β-galactoside (ONPG) substrate and lactose at physiological pH (5-7), with optimal temperatures between 30-37°C. Even though further optimization is required, these enzymes represent interesting candidates for the production of value-added products from dairy industries by-products.