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An acid-tolerant and cold-active β-galactosidase potentially suitable to process milk and whey samples

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Abstract

A novel β-galactosidase gene (galM) was cloned from an aquatic habitat metagenome. The analysis of its translated sequence (GalM) revealed its phylogenetic closeness towards Verrucomicrobia sp. The sequence comparison and homology structure analysis designated it a member of GH42 family. The three-dimensional homology model of GalM depicted a typical (β/α)8 TIM-barrel containing the catalytic core. The gene (galM) was expressed in a heterologous host, Escherichia coli, and the purified protein (GalM) was subjected to biochemical characterization. It displayed β-galactosidase activity in a wide range of pH (2.0 to 9.0) and temperature (4 to 60 °C). The heat exposed protein showed considerable stability at 40 and 50 °C, with the half-life of about 100 h and 35 h, respectively. The presence of Na, Mg, K, Ca, and Mn metals was favorable to the catalytic efficiency of GalM, which is a desirable catalytic feature, as these metals exist in milk. It showed remarkable tolerance of glucose and galactose in the reaction. Furthermore, GalM discerned transglycosylation activity that is useful in galacto-oligosaccharides’ production. These biochemical properties specify the suitability of this biocatalyst for milk and whey processing applications.

Key points

• A novel β-galactosidase gene was identified and characterized from an aquatic habitat.

• It was active in extreme acidic to mild alkaline pH and at cold to moderate temperatures.

• The β-galactosidase was capable to hydrolyze lactose in milk and whey.

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Data availability

The sequence of galM gene is available in the NCBI GenBank under the accession number OL412003.

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Acknowledgements

The authors acknowledge the Department of Biotechnology (DBT), Govt. of India, for financial support. M. T. acknowledges the CSIR fellowship. S. P. S. and A. K. R. acknowledge the DBT research project, BT/PR31829/NDB/39/649/2019.

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M. T. performed all the experiments, analyzed the data, and drafted the manuscript. S. P. S. conceived, designed, and supervised the study, analyzed the data, and drafted the manuscript. A. K. R. contributed to study design, data analysis, and reviewed the manuscript. All authors read and approved the final manuscript.

Corresponding authors

Correspondence to Amit Kumar Rai or Sudhir P. Singh.

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The authors declare no competing interests.

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Thakur, M., Kumar Rai, A. & Singh, S.P. An acid-tolerant and cold-active β-galactosidase potentially suitable to process milk and whey samples. Appl Microbiol Biotechnol 106, 3599–3610 (2022). https://doi.org/10.1007/s00253-022-11970-7

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  • DOI: https://doi.org/10.1007/s00253-022-11970-7

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