Isolation an Aldehyde Dehydrogenase Gene from Metagenomics Based on Semi-nest Touch-Down PCR

Culture-independent approaches to analyze metagenome are practical choices for rapid exploring useful genes. The mg-MSDH gene, acquired from the hot spring metagenomic, was retrieved full lengths of functional gene using semi-nest touch-down PCR. Two pairs of degenerate primers were used to separate seven conserve partial sequences by semi-nest touch-down PCR. One of them showed similarity with aldehyde dehydrogenase was used as a target fragment for isolating full-length sequence. The full-length mg-MSDH sequence contained a 1,473 bp coding sequence encoding a 490-amino-acid polypeptide and assigned an accession number JQ715422 in Genbank. The upstream sequences TAGGAG of the start codon (GTG), suggested that was a ribosome binding site. The coding sequence of mg-MSDH was ligated to pET-303 vector and the reconstructive plasmid was successfully overexpressed in E. coli. The purified recombinant mg-MSDH enzyme showed propionaldehyde oxidative activity of 3.0 U mg(-1) at 37 °C.