High yield recombinant thermostable α-amylase production using an improved Bacillus licheniformis system

Background: Some strains of Bacillus licheniformis have been improved by target-directed screening as well as by classical genetic manipulation and used in commercial thermostable alpha-amylase and alkaline protease production for over 40 years. Further improvements in production of these enzymes are desirable. Results: A new strain of B. licheniformis CBBD302 carrying a recombinant plasmid pHY-amyL for Bacillus licheniformis alpha-amylase (BLA) production was constructed. The combination of target-directed screening and genetic recombination led to an approximately 26-fold improvement of BLA production and export in B. licheniformis. Furthermore, a low-cost fermentation medium containing soybean meal and cottonseed meal for BLA production in shake-flasks and in a 15 liter bioreactor was developed and a BLA concentration of up to 17.6 mg per ml growth medium was attained. Conclusion: This production level of BLA by B. licheniformis CBBD302(pHY-amyL) is amongst the highest levels in Gram-positive bacteria reported so far.