Abstract: With the development of modern starch industry,looking for new acid-stable α-amylase become a research hot spot.AF1 producing acid-stable α-amylase with high enzyme activity was isolated from the PDA medium.It was identified as Bacillus amyloliquefaciens based on morphological characteristics,physiological and biochemical characteristics and 16S rDNA gene sequence.Its enzymatic properties showed that the optimal reaction temperature was 75 ℃,the pH was 5.0.Its enzyme activity remained at more than 80% in pH 5.0-7.0 for 1 h.It was stable under the temperature of 60 ℃.But its activity decreased significantly up to 70 ℃,even decreased to zero at 80 ℃ for only 30 min.Also,this α-amylase was inhibited obviously by Cu²⁺ but not affected by Na⁺, Ca²⁺, Ba²⁺, Mg²⁺ and EDTA.It was indicated that the α-amylase from AF1 was an acid-stable α-amylase with Ca²⁺ independent.This α-amylase can be used together with glucoamylase avoiding pH adjustment and no Ca²⁺ added into the reaction system to keep the stability of the α-amylase during the starch processing.Hence,the process was simpler and the cost was lower when the liquefaction and saccharification process at the same time under low acid condition with this α-amylase.

Key words: Bacillus amyloliquefaciens, strain identification, acid-stale &alpha, -amylase, enzymatic property