[Purification and characterization of thermostable amylases from two bacterial species]

Two thermophilic bacterial isolates, strain 173 and strain 174, with raw starch-digesting activities were selected from thermophilic bacteria growing in hot spring of Tengchong County, Yunnan Province, China. By amplification, sequencing and alignment analysis of 16S ribosomal DNAs, they were identified as members of genus Geobacillus. In shaker flask culture Geobacillus sp. 173 produced 14.5 U/mL amylase and for Geobacillus sp. 174 with 12.9 U/mL. Both amylases were purified by starch absorption-desorption and chromatograph. The amylases from strain 173 and strain 174 purified to about 50 and 29 folds were respectively achieved with an overall yield of 34% and 41%. The maximum gelatinized-starch-digesting activity of the purified amylases were at 70 degrees C and pH 5.0 - 5.5. The high raw-starch-digesting activity of these enzymes were observed at 50 degrees C - 60 degrees C (from strain 173) and 40 degrees C - 60 degrees C (from strain 174). Both enzymes were not sensitive to ions including mental ions (Na+, K+, Mg2+, Ca2+, Mn2+, Zn2+) and others (EDTA, Citrate), but were slightly inhibited by ions such as Co2+, Cu2+ for amylase from strain 173 and Cu2+ for amylase from strain 174. Both enzyme had specificity of starch substrates.