High-level production of α-amylase by manipulating the expression of alanine racamase in Bacillus licheniformis

To improve target protein production by manipulating expression levels of alanine racemase in Bacillus licheniformis. The gene of dal was identified to be responsible for alanine racemase function. Based on the selection marker of dal, a food-grade expression system was constructed in B. licheniformis, and effects of different dal expression levels mediated by promoters on alpha-amylase production were investigated. The highest alpha-amylase activity (155 U/ml) was obtained in BL10D/pP43SAT-PtetDal, increased by 27% compared with that of the control strain BL10/pP43SAT in tetracycline-based system (123 U/ml). Moreover, the dal transcriptional level was not correlated positively with that of amyL. A food-grade system for high-level production of alpha-amylase was constructed in B. licheniformis, revealing that expression levels of selection marker significantly affected target protein production.