Purification and characterization of an extracellular esterase with organic solvent tolerance from a halotolerant isolate, Salimicrobiumsp. LY19

Li Xin,Yu Hui-Ying

doi:10.1186/1472-6750-13-108

Abstract

BackgroundHalotolerant bacteria are excellent sources for selecting novel enzymes. Being intrinsically stable and active under high salinities, enzymes from these prokaryotes have evolved to function optimally under extreme conditions, making them robust biocatalysts with potential applications in harsh industrial processes.ResultsA halotolerant strain LY19 showing lipolytic activity was isolated from saline soil of Yuncheng Salt Lake, China. It was identified as belonging to the genus of Salimicrobium by 16S rRNA gene sequence analysis. The extracellular enzyme was purified to homogeneity with molecular mass of 57 kDa by SDS-PAGE. Substrate specificity test revealed that the enzyme preferred short-chain p-nitrophenyl esters and exhibited maximum activity towards p-nitrophenyl butyrate (p-NPB), indicating an esterase activity. The esterase was highly active and stable over broad temperature (20°C-70°C), pH (7.0-10.0) and NaCl concentration (2.5%-25%) ranges, with an optimum at 50°C, pH 7.0 and 5% NaCl. Significant inhibition of the esterase was shown by ethylenediaminetetraacetic acid (EDTA), phenylmethylsulfonyl fluoride (PMSF) and phenylarsine oxide (PAO), which indicated that it was a metalloenzyme with serine and cysteine residues essential for enzyme activity. Moreover, the esterase displayed high activity and stability in the presence of hydrophobic organic solvents with log Pow ≥ 0.88 than in the absence of an organic solvent or in the presence of hydrophilic solvents.ConclusionsResults from the present study indicated the novel extracellular esterase from Salimicrobium sp. LY19 exhibited thermostable, alkali-stable, halotolerant and organic solvent-tolerant properties. These features led us to conclude that the esterase may have considerable potential for industrial applications in organic synthesis reactions.

Highlights

Halotolerant bacteria are excellent sources for selecting novel enzymes
It is able to grow in media containing 0-30% (w/v) NaCl and grows optimally at 4% (w/v) NaCl. This bacterium can be considered as a halotolerant microorganism [10]
Phylogenetic analysis based on 16S rRNA gene sequence comparisons revealed the strain LY19 belonged to the genus of Salimicrobium and was most closely related to Salimicrobium halophilum DSM 4771 T (98.6% 16S rRNA gene sequence similarity) (Figure 1)

Summary

Introduction

Halotolerant bacteria are excellent sources for selecting novel enzymes. Being intrinsically stable and active under high salinities, enzymes from these prokaryotes have evolved to function optimally under extreme conditions, making them robust biocatalysts with potential applications in harsh industrial processes. Esterases (EC 3.1.1.1) represent a family of hydrolases that catalyze the hydrolysis and formation of shortchain fatty acid esters. Because of their broad substrate specificity, highly chemo-, regio-, enantio-selectivity and non-aqueous catalytic properties [1], they have diverse applications in biotechnology which are used as additives in laundry detergents and stereo-specific biocatalysis in pharmaceutical production [2]. Since salt tends to greatly reduce water activity like organic solvents, enzymes from halotolerant microorganisms may become the choice for biocatalytic processes performed in low water activity environments [8]. Numerous organic solvent-tolerant microbial esterases have been reported [9]; published studies on the enzymatic behavior of esterases from halotolerant bacteria in non-aqueous media are scarce. Purification and characterization of its extracellular esterase, especially its activity and stability in the presence of organic solvents, were reported

Methods

Results

Discussion

Conclusion