Mei-Ping Cheng

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.

Poultry-litter biochars (PLBs), which were prepared at two pyrolytic temperatures, were applied to the soils of croplands with four consecutive harvests of water spinach to assess the effects of PLBs on the soil properties and the growth of water spinach. The results show that PLB amendment resulted in an increase of soil pH. The electrical conductivity values, and the concentrations of extractable inorganic nitrogen, exchangeable potassium, and available phosphorus in the soils drastically increased in the 0.5% and 1% biochar-amended soils. However, most of the significant changes due to PLB amendment disappeared after four consecutive harvests of water spinach. The growth of water spinach was enhanced in the soils amended with PLBs, especially the one prepared at 350 °C. Nonetheless, the application of 1% PLBs to the soil resulted in an imbalance between calcium and magnesium in water spinach.

In this study, a low-cost adsorbent was prepared from rice straw without any activation process and studied for the adsorption capacities and mechanisms of Cd and Pb ions in water. The adsorption of these metal ions on rice-straw char (RSC) was fast and reached equilibrium within 24 h. The adsorption isotherms exhibited the L-type and the adsorption capacities of Pb(II) and Cd(II) at pH 4 were determined to be 68 and 26 μmol g⁻¹, respectively. The difference between the adsorption capacities of these two metal ions implied different adsorption mechanisms. The adsorptions of Pb(II) and Cd(II) both increased with increasing pH. The adsorption of Pb(II) was insensitive to ionic strength, and the adsorption edge was significantly lower than the PZC of RSC. On the contrary, the adsorption of Cd(II) was affected by changing ionic strength, and the adsorption edges was close to the PZC of RSC. Based on these results, the adsorption mechanism of Pb(II) was determined to be inner-sphere complexation, whereas Cd(II) interacted with the RSC surface through electrostatic attraction and formed outer-sphere complexes on RSC.