Zongze Shao

Molecular Cloning, Purification, and Characterization of a Novel, Acidic, pH-Stable Endoglucanase from Martelella mediterranea

A novel gene encoding an endoglucanase designated Cel5D was cloned from a marine bacterium Martelella mediterranea by genomic library. The gene had a 1,113 bp opening reading frame encoding a 371-amino-acid protein with a molecular mass of 40,508 Da and containing a putative signal peptide (41 amino acids). Cel5D had low similarity (48–51% identity) with other known endoglucanases and consisted of one single catalytic domain, which belonged to the glycosyl hydrolase family 5. The maximum activity of Cel5D was observed at 60°C and pH 5.0. Cel5D displayed broad pH stability within the range of pH 3.0–11.0 and retained hydrolytic activity in the presence of a wide variety of metal ions and some chemical reagents. These characteristics suggest that the enzyme has considerable potential in industrial applications.

Cel8H, a novel endoglucanase from the halophilic bacterium Halomonas sp. S66-4: molecular cloning, heterogonous expression, and biochemical characterization.

A recombinant Escherichia coli clone expressing an endoglucanase was identified from a genomic library of the halophilic bacterium Halomonas sp. S66-4, and the enzyme was designated Cel8H. The cel8H gene consisted of 1,053 bp and encoded 350 amino acids sharing the highest identity of 48% to other known endoglucanases. The protein was expressed in E. coli BL21 (DE3) and purified to homogeneity. The purified recombinant enzyme had an optimal activity of 4.9 U/mg at pH 5 and 45°C toward the substrate carboxymethylcellulose. It exhibited extraordinary properties which differed from endoglucanases reported previously at the point of high salt tolerance above 5 M, simultaneously with high pH stability at pH 4–12 and high temperature stability at 40–60°C. Various substrate tests indicated that the enzyme hydrolyzes β-1,4-glucosidic bonds specifically.

A Novel Bioassay for High-Throughput Screening Microorganisms with N-acyl Homoserine Lactone Degrading Activity

A novel biosensor strain (Escherichia coli ALM403) that responded to N-acyl homoserine lactone (AHL) was constructed using a luxR-Plux cassette as a regulatory sequence and β-mannanase as a reporter gene. Dinitrosalicylic acid method was used to detect the response of the sensor strain to N-acyl homoserine lactone. By investigating the response to a range of concentrations of N-β-oxooctanoyl-l-homoserine lactone (OOHL), it was demonstrated that the expression of mannanase in E. coli ALM403 could be greatly enhanced by OOHL and resulted in an assayable phenotype. A high-throughput screening approach was developed to isolate AHL-degrading microorganisms, and a marine Halomonas sp. S66-4 showing a marked AHL-degrading ability was successfully isolated. In conclusion, the bioassay system provided a simple and efficient approach to isolate AHL-degrading bacteria.