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Background  The development of a new cold-active β-D-galactosidases and microorganisms that efficiently ferment lactose is of high biotechnological interest, particularly for lactose removal in milk and dairy products at low temperatures and for cheese whey bioremediation processes with simultaneous bio-ethanol production.    Results  In this article, we present a new β-D-galactosidase as a candidate to be applied in the above mentioned biotechnological processes. The gene encoding this β-D-galactosidase has been isolated from the genomic DNA library of Antarctic bacterium  Arthrobacter  sp. 32c, sequenced, cloned, expressed in  Escherichia coli  and  Pichia pastoris , purified and characterized. 27 mg of β-D-galactosidase was purified from 1 L of culture with the use of an intracellular  E. coli  expression system. The protein was also produced extracellularly by  P. pastoris  in high amounts giving approximately 137 mg and 97 mg of purified enzyme from 1 L of  P. pastoris  culture for the AOX1 and a constitutive system, respectively. The enzyme was purified to electrophoretic homogeneity by using either one step- or a fast two step- procedure including protein precipitation and affinity chromatography. The enzyme was found to be active as a homotrimeric protein consisting of 695 amino acid residues in each monomer. Although, the maximum activity of the enzyme was determined at pH 6.5 and 50°C, 60% of the maximum activity of the enzyme was determined at 25°C and 15% of the maximum activity was detected at 0°C.    Conclusion  The properties of  Arthrobacter  sp. 32cβ-D-galactosidase suggest that this enzyme could be useful for low-cost, industrial conversion of lactose into galactose and glucose in milk products and could be an interesting alternative for the production of ethanol from lactose-based feedstock.

A new cold-adapted β-D-galactosidase from the Antarctic Arthrobacter sp. 32c – gene cloning, overexpression, purification and properties