Isolation and characterization of cold-active family VIII esterases from an arctic soil metagenome

Functional screening for lipolytic enzymes at low temperatures resulted in the isolation of the novel cold-active esterases, EstM-N1 and EstM-N2, from a metagenomic DNA library of arctic soil samples. EstM-N1 and EstM-N2 were 395 and 407 amino acids in length, respectively, and showed the highest similarity to class C β-lactamases. However, they shared a relatively low level of sequence similarity (30%) with each other. Phylogenetic analysis of bacterial lipolytic enzymes confirmed that EstM-N1 and EstM-N2 belonged to family VIII of bacterial esterases/lipases. The (His)₆-tagged esterases were purified to about 99% homogeneity from the soluble fraction of recombinant Escherichia coli cultures. The purified EstM-N1 and EstM-N2 retained more than 50% of maximal activity in the temperature range of 0-35°C, with optimal temperatures of 20°C and 30°C, respectively. Both enzymes preferred the short acyl chains of p-nitrophenyl esters and exhibited very narrow substrate specificity, indicating that they are typical esterases. The β-lactamase activity of EstM-N1 and EstM-N2 was also detected and reached about 31% and 13% of the positive control enzyme, Bacillus cereus β-lactamase, respectively. These first cold-active esterases belonging to family VIII are expected to be useful for potential biotechnological applications as interesting biocatalysts.