A novel esterase from a psychrotrophic bacterium Psychrobacter celer 3Pb1 showed cold-adaptation and salt-tolerance

A genomic library of a psychrotrophic Psychrobacter celer 3Pb1 was constructed and screened for lipolytic proteins, and a novel esterase Est12 was cloned and characterized. The esterase gene, est12, contained an open reading frame of 990 bp that encoded a protein of 329 amino acids with an estimated molecular mass of 35,150 Da. Est12 displayed the highest amino acid identity (77%) with a hypothetical esterase from Psychrobacter sp. PAMC 21119 (WP_010200623.1). Phylogenetic analysis suggested that the protein belonged to a new lipase/esterase family. Substrate specifity study showed that Est12 preferred short-chain p-nitrophenyl esters and was most active toward p-nitrophenyl butyrate. Est12 displayed the optimal activity at pH 7.5 and 35 °C, and remained 41% activity at 0 °C while being unstable at temperatures above 40 °C, indicating its cold-adaptation. Besides, Est12 was a salt-tolerant esterase as 4.5 M NaCl significantly declined Km from 0.069 to 0.033 mM and increased kcat from 4.20 to 9.21 s−1, resulting in the increased catalytic efficiency kcat/Km from 60.72 to 276.31 s−1 mM−1. The enzyme activity was also quite stable after 24 h incubation in 0–4.5 M NaCl solutions. In addition, Est12 was very active and stable in the presence of several detergents and organic solvents. This new cold-active and halotolerant esterase would be a potential candidate in industrial applications under extreme conditions (low temperatures, high salinity), and was valuable for studying other unknown esterases/lipases in this new family.