Molecular Cloning and Characterization of a New Family VI Esterase from an Activated Sludge Metagenome.

A new esterase gene, est6, was discovered in an activated sludge metagenomic library. The 729-bp gene encodes a 242-amino acid protein (designated Est6) with a molecular mass of 26.1 kDa. Est6 shared only a moderate identity to a putative hydrolase with the highest BLASTP analysis score. Most of the closely related proteins are uncharacterized and are predicted from genome sequencing data of microorganisms or metagenomic DNA sequences. The phylogenetic analysis of Est6 showed that the protein was assigned to family VI esterases/lipases. The catalytic triad of Est6 was predicted to be Ser135, Asp188, and His219, with Ser135 in a typically conserved pentapeptide (GFSQG) of family VI members, which was further confirmed by site-directed mutagenesis. The est6 gene was overexpressed successfully in its soluble form in Escherichia coli and then purified to its tag-free form and homogeneity by affinity chromatography. The purified Est6 in pH 8.0 buffer was active as a monomer. The optimal conditions for Est6 activity were at a temperature of 45 °C and pH of 8.0 when using p-nitrophenyl acetate as a substrate. The enzyme was stable over wide temperature and pH ranges, and it exhibited activity in the presence of organic solvents, metal cations, or detergents. Furthermore, the enzyme showed significant regioselectivity in the spectrophotometric analysis. In conclusion, Est6 might have the potential for applications in biotechnological processes.

Nonylphenol reduces sperm viability and fertility of mature male breeders in Brown Tsaiya ducks (Anas platyrhynchos).

The aim of this study was to investigate the effect of nonylphenol (NP), a widely used surfactant, on the reproductive performance of male Brown Tsaiya ducks (Anas platyrhynchos) (MBBTDs). Mature MBBTDs (n=100) were treated with NP by daily gavaging of 0, 1 (NP1), 10 (NP10) and 250 (NP250) mg/kg-BW/d for 14 wk. Semen quality, fertilization rate and specific factors in blood plasma were measured. Weights of organs were also measured at 14 wk after NP administration. Ducks from each treatment (n=4) were continually treated with NP thereafter for 12 mo to observe changes of tissue ultrastructure by microscopic examination. The results showed that ducks treated with amounts of NP of greater than 1mg NP/kg BW/d (NP1) for 14 wk had decreased sperm viability (32.3%) compared to those in the control group (74.1%, P<0.05). The fertilization rate of ducks treated with 250mg NP/kg-BW/d (NP250) for 14 wk was reduced (21.0%) compared to the control group (74.5%, P<0.05). Plasma aminotransferase (AST) and alanine aminotransferase (ALT) activities were also greater in NP250 group at the 14th wk post-treatment. Plasma testosterone concentrations were increased by NP1 treatment at the 14th wk post-treatment. Administration at dosage 250mg NP/kg-BW/d for 12 mo resulted in reduced sperm counts (P<0.05) and histopathological changes, such as dilated seminiferous tubules (P<0.05) and degenerated spermatocytes (P<0.05). These findings strongly suggest that NP adversely affects the reproductive performance of MBBTDs.

Use of metagenomic approaches to isolate lipolytic genes from activated sludge.

The aims of this study were to access the bacterial diversity and isolate lipolytic genes using the metagenomic approach in activated sludge of a swine wastewater treatment facility. On the basis of BLASTN analysis of 16S rRNA gene clones, most of these communities (90%) were of uncultivated bacteria. The metagenomic library was constructed using a plasmid vector and DNA extracted directly from activated sludge samples. The average insert size was approximately 5.1 kb. A total of 12 unique and lipolytic clones were obtained using the tributyrin plate assay. The rate of discovering a lipolytic clone in this study was as high as 0.31%. Molecular analysis revealed that most of the 16 putative lipolytic enzymes showed 28-55% identity with non-redundant protein sequences in the database. Briefly, this study demonstrates that activated sludge is an ideal bioresource for isolating new lipolytic enzymes.

Enhanced chlorophenol sorption of soils by rice-straw-ash amendment.

Rice-straw burning is a common post-harvest practice on rice paddy land, which results in the accumulation of rice-straw ash (RSA) in paddy soil. Because the occurrence of RSA in soil may affect the fate and transport of contaminants, this study investigated the sorption of 3-chlorophenol (3-CP) on RSA and RSA amended soils to evaluate the sorptive properties of RSA in soils. The results showed that the sorption of 3-CP to RSA proceeds through a surface reaction rather than through partitioning and that the neutral form of 3-CP is preferentially sorbed to the surface when compared to the deprotonated anionic form of 3-CP. The addition of RSA to the soils enhanced the overall 3-CP sorption, indicating that RSA amendment may be applied to retard the movement of 3-CP in contaminated soils. As the RSA content in the soils was increased from 0% to 2%, the Langmuir sorption maximum of the soils increased from 18-80 to 256-274 mg kg(-1). Thus, RSA contributed more to the total sorption of the soils than other major components in the soils. Nonetheless, the 3-CP sorption of the soils containing RSA was less than the combination of pure RSA and the soils, thereby indicating that the 3-CP sorption of RSA was suppressed. This may be attributed to the competition of organic matter or other soil components for the surface binding sites of RSA.