Vector promoters used in Klebsiella pneumoniae.

Much effort has been devoted to the metabolic engineering of Klebsiella pneumoniae; however, our knowledge of the actual expression level of promoters used in K. pneumoniae is limited. In this study, the expression levels of three promoters were compared systematically by using the lacZ reporter gene with different carbon sources in K. pneumoniae. The results showed that, although promoters P T5 and P tac designed for Escherichia coli were functional, P T5 appeared more efficient and the induction/repression ratio of P tac was decreased extremely in K. pneumoniae. The basal level of P tac for lacZ expression reached 396.5 U/mg, which was 9.5-fold higher compared with P T5 in LB medium, indicating P tac can be used as an efficient 'constitutive' promoter as well as an efficient induced promoter in K. pneumoniae. In different carbon sources medium, a newly constructed endogenous constitutive P bud proved to be a stable and weak promoter. On the basis of our data, a set of P bud and P tac promoters could meet the broad range (about 1,000 orders of magnitude) of gene expression needed for engineered K. pneumoniae in glycerol-based medium. [ABSTRACT FROM AUTHOR]