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KMID : 0545120110210030236
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Journal of Microbiology and Biotechnology
2011 Volume.21 No. 3 p.236 ~ p.242
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Molecular Characterization of Cold-Inducible β-Galactosidase from Arthrobacter sp. ON14 Isolated from Antarctica
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Ke Xu
Xixiang Tang
Yingbao Gai
Muhammad Aamer Mehmood
Xiang Xiao
Fengping Wang
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Abstract
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A psychrotrophic bacterium, Arthrobacter sp. ON14, isolated from Antarctica, was shown to exhibit a high β-galactosidase activity at a low temperature. A genomic library of ON14 was constructed and screened for β-galactosidase genes on functional plates containing 5-bromo-4-chloro-3-indolyl- β-D-galactopyranoside (X-gal) as the substrate. Two different β-galactosidase genes, named as galA, galB, were found in ON14. Computational analyses of the genes revealed that the encoded protein GalA belongs to family 2 of glycosyl hydrolysases and is a cold-active protein, whereas GalB belongs to family 42 of glycosyl hydrolysases and is a mesophilic protein. Reverse transcription analyses revealed that the expression of galA is highly induced at a low temperature (4oC) and repressed at a high temperature (28oC) when lactose is used as the sole carbon source. Conversely, the expression of galB is inhibited at a low temperature and induced at a high temperature. The purified GalA showed its peak activity at 15oC and pH 8. The mineral ions Na+, K+, Mg2+, and Mn2+ were identified as enzyme activators, whereas Ca2+ had no influence on the enzyme activity. An enzyme stability assay revealed that the activity of GalA is significantly decreased when it is incubated at 45oC for 2 h, and all its activity is lost when it is incubated at 50oC.
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KEYWORD
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β-galactosidase, cold inducible, Arthrobacter
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