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A functional screen of a metagenomic library from "Upo" swamp sediment in Korea identified a gene EstL28, the product of which displayed lipolytic properties on a tributyrin-supplemented medium. The EstL28 sequence encodes a 290 amino acid protein (designated as EstL28), with a predicted molecular weight of 31.3 kDa. The encoded EstL28 protein exhibited the highest sequence similarity (45 %) to a hydrolase found in Streptococcus sanguinis. Phylogenetic analysis indicated that EstL28 belongs to a currently uncharacterized family of esterases. Within the conserved alpha/beta-hydrolase 6 domain, the EstL28 retains the catalytic triad Ser(103)-Asp(248)-His(268) that is typical of esterases. The Ser(103) residue in the catalytic triad is located in the consensus pentapeptide motif GXSXG. The purified EstL28 enzyme worked optimally at 35 A degrees C and pH 8.5 and remained stable at temperatures lower than 20 A degrees C. The catalytic activity of EstL28 was maximal with p-nitrophenyl butyrate, indicating that it was an esterase. This enzyme also exhibited stable activity in the presence of methanol, ethanol, isopropanol, and dimethyl sulfoxide. Therefore, the level of stability in organic solvents and cold temperature suggests that EstL28 has potential for many biotechnological applications.