Cloning, expression and functional analyses of the catabolite control protein CcpA from Bacillus megaterium

A mutant of Bacillus megaterium relieved from catabolite repression has been used to clone ccpA from B. megaterium by complementation. ccpA is the first gene of a presumed operon, in which it is followed by the motA homologue ORF1 and the motB homologue ORF2. The mutation maps in the 3'-terminal region of ccpA, where an in-frame duplication of 84 nucleotides located between two 9 bp direct repeats leads to an insertion of 28 amino acids near the C-terminus of CcpA. An in-frame deletion of 501 bp in ccpA exhibits the same phenotype as the 84 bp duplication. Deletion of ORF1 and ORF2 does not yield an apparent phenotype. A single-copy ccpA::lacZ transcriptional fusion is constitutively expressed, independent of whether the growth medium triggers catabolite repression or not. The ccpA mutation leads to relief of catabolite repression exerted by glucose, fructose, mannitol, glucitol and glycerol, whereas only smaller effects were found with ribose, citrate and glutamate. The respective growth rates on these carbon sources are uniformly reduced to a generation time of about 90 min in the ccpA mutant. Catabolite repression of a plasmid-encoded xylA::ccpA fusion is less efficient than that of a xylA::lacZ fusion in the same vector. Furthermore, overproduction of CcpA decreases catabolite repression of a single-copy xylA::lacZ fusion approximately twofold. Thus, overexpression of CcpA may be counterproductive for catabolite repression, supporting the hypothesis that CcpA by itself may not bind sufficiently strongly to the cis-active catabolite-responsive element to exert catabolite repression.