Abstract: A strain L2004 was obtained by screening model of cold-active β-galactosidase from 101 strains isolated from the sample of permafrost, refrigeration dairy products under 4 ℃. Based on morphological, physiology and biochemistry properties, the strain l2004 was identified as belonging to the genus Brevibacillus. The growth characteristics of the psychrotrophic bacterium L 2004 were studied, and the results showed that the optimal temperature for growth and enzyme production of the strain is about 20 ℃ and 15 ℃ respectively. The maximum enzyme activity occurred at pH 9 for L2004, and the optimal temperature of β-galactosidase action was about 33℃with ONPG as the substrate. β-galactosidase activity under 0 ℃ exhibited nearly 25% of the maximum activity, stimulated by Mg2+ and Mn2+, inhibited by Zn2+, Cu2+ and Hg2+. Moreover, Km of the cold-active β- galactosidase activity for ONPG from strain L2004 is of found to be 52.9 mmol/L at 30 ℃ Therefore the cold-active β- galactosidase of Brevibacillus sp. L2004 has particular advantage for producing lactose-reduced dairy at low temperature. The strain L2004 gives a maximum β-galactosidase activity of 80 U/ml in shaking flask after 48 h cultivation at 20 ℃ and 200 r/min when growing in a medium containing tryptone 37.5 g/L, soya peptone 5 g/L, lactose 6 g/L, yeast extract 4.5 g/L, KH2PO4 2.5 g/L and NaCl 7.5 g/L.

Key words: cold-active &beta, -galactosidase； enzyme property； fermentation； Brevibacillus；