Screening, identification and fermentation optimization of a newly isolated raw starch digesting amylase-producing strain Bacillus sp. GEL-09

Abstract:

[Background] Raw starch digesting amylase can directly degrade raw starch granules below the gelatinization temperature. Hence, it has been wildly used in the production of bioethanol, Chinese spirit, yellow rice wine and vinegar. [Objective] This study aims at isolation and identification new raw starch digesting amylase-producing strain, to provide enzyme resource that can be used in the process of fermentation with uncooked materials. [Methods] With tapioca starch as sole carbon source, raw starch digesting amylase-high producing strain was isolated from soil of cassava field. Then, it was identified by analysis of colony morphology, photomicrographs, and 16S rRNA gene sequence. Single factor experiment was used to optimize the medium component and fermentation conditions. The enzyme was purified and characterized. [Results] Strain GEL-09 was isolated and identified as a species of the genus Bacillus, designated as Bacillus sp. GEL-09. The raw starch digesting amylase production was optimized by varying culture conditions. On the optimal culture condition, the maximal enzyme production was 430.6 U/mL, which was 2.8 folds of that before optimization. The enzyme showed highest activity at 50 °C and pH 7.0. Its raw starch digestion ability value was 62.3%, which was higher than that of the α-amylase, maltogenic α-amylase or β-amylase. [Conclusion] Bacillus sp. GEL-09 has great development potential and application prospects in the production of raw starch digesting amylase.