Characterization of a cypermethrin-degrading Methylobacterium sp strain A-1 and molecular cloning of its carboxylesterase gene

A novel mesophilic bacterial strain, designated A-1, was isolated from microbially contaminated biopolymer microcapsules. The bacterium was able to withstand and grow in liquid cultures supplemented with the pyrethroid cypermethrin in concentrations up to 400mgL(-1). Furthermore, strain A-1 could use cypermethrin as sole carbon source and could degrade >50% of it in 12h. Based on phenotypic and chemotaxonomic characterization, and phylogenetic analysis of 16S rRNA gene sequence, the strain A-1 was identified as Methylobacterium sp., which is the first reported cypermethrin degrader of methylotrophic bacteria. A role for esterase activity in cypermethrin biodegradation was presumed. Therefore, the carboxylesterase gene mse1 was amplified from the Methylobacterium sp. strain A-1 genome and the resulting 1kb amplicon cloned into E. coli. Sequence analysis of the mse1-DNA insert revealed an open reading frame of 633bp encoding for a putative carboxylesterase of 210 amino acid residues with a predicted molecular mass of 22kDa. The amino acid sequence of the deduced enzyme MsE1 with the catalytic triad Ser(106), Asp(156), and His(187) was found to be similar to that of /-hydrolase fold proteins. The active site Ser(106) residue is located in the consensus pentapeptide motif Gly-X-Ser-X-Gly that is typical of esterases.