Isolation and characterization of a novel organic solvent-tolerant and halotolerant esterase from a soil metagenomic library

Soil metagenome conceals a great variety of unexploited genes for industrially important enzymes. To identify novel genes conferring lipolytic activity, one metagenomic library comprising of 200,000 transformants were constructed. Among the 48,000 clones screened, 19 clones which exhibited lipolytic activity were obtained. After sequence analysis, 19 different lipolytic genes were identified. One of these genes, designated as estWSD, consisted of 1152 nucleotides, encoding a 383-amino-acid protein. Multiple sequence alignment and phylogenetic analysis indicated that EstWSD and its closest homologues may constitute a new family of bacterial lipolytic enzymes. The best substrate for the purified EstWSD among the ρ-nitrophenol esters examined was ρ-nitrophenol butyrate. Recombinant EstWSD displayed a pH optimum of 7.0 and a temperature optimum of 50 °С. This enzyme retained 52% of maximal activity after incubation at 50 °C for 3 h. Furthermore, EstWSD also exhibited salt tolerance with over 51% of its initial activity in the presence of up to 4.5 M NaCl for 1 h. In particular, this enzyme showed remarkable stability in 15% and 30% dimethylsulfoxide, ρ-xylene, hexane, heptane, and octane even after incubation for 72 h. To our knowledge, it is the first report to find a novel esterase belonging to a new lipolytic family and possessing such variety of excellent features. All these characteristics suggest that EstWSD may be a potential candidate for application in industrial processes.