Characterization of the Thermophilic Starch Degrading Petrotoga Strain 64G3 and the Expression of its α-amylase Gene

A starch degrading bacterial isolate 64G3 was taxonomically characterized. Based on physiological properties, 16S rDNA sequence analysis and DNA-DNA hybridization, this isolate was assigned to Petrotoga mexicana species. A gene encoding an α-amylase of this strain was cloned and overexpressed in Escherichia coli. The gene is 1, 992 bp long encoding a polypeptide of 663 amino acids with a calculated molecular mass of 77, 042 Da. The deduced amino acids sequence shows a high identity of 94% with Petrotoga mobilis SJ95 α-amylase but low identities (up to 45%) with other glycosyl hydrolase family 13 enzymes. Recombinant amylase produced in Escherichia coli showed hydrolytic activity towards amylose, amylopectin, glycogen and maltooligosaccharides but not pullulan or other types of cyclodextrins. The optimal temperature and pH for the enzyme activity on starch were 45°C and 6.5, respectively. The enzyme cleaved soluble starch in endo-acting manner to release maltose, maltotriose and a minor amount of glucose during hydrolysis.