Isolation and characterisation of a novel alpha-amylase from the extreme haloarchaeon Haloterrigena turkmenica

An extracellular halophilic alpha-amylase (AmyA) was produced by the haloarchaeon Haloterrigena turkmenica grown in medium enriched with 0.2% (w/v) starch. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion chromatography (SEC) analyses showed a major band at 66.0 kDa and a peak of 54.0 kDa, respectively. Analysis of tryptic fragments of the protein present in the major SDS-PAGE band by nano-LC-ESI⿿MS/MS led to identification of the alpha-amylase catalytic region, encoded by the htur2110 gene, as the protein possessing the described activity. Optimal values for activity were 55 °C, pH 8.5 and 2 M NaCl, and high thermostability was showed at 55 °C and 3 M NaCl. AmyA activity was enhanced by Triton X-100 and was not influenced by n-hexane and chloroform. Starch hydrolysis produced different oligomers with maltose as the smallest end-product. The efficiency of AmyA in degrading starch contained in agronomic residues was tested in grape cane chosen as model substrate. Preliminary results showed that starch was degraded making the enzyme a potential candidate for utilization of agro-industrial waste in fuel and chemicals production. AmyA is one of the few investigated amylases produced by haloarchaea, and the first alpha-amylase described among microorganisms belonging to the genus Haloterrigena.