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J. Bacteriol. doi:10.1128/JB.00449-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

CcpA-dependent and -independent control of beta-galactosidase expression in Streptococcus pneumoniae occurs via regulation of an upstream PTS-encoding operon

Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294

^* To whom correspondence should be addressed. Email: jyother{at}uab.edu.

	Abstract

A spontaneous mutant of Streptococcus pneumoniae strain D39 exhibiting elevated -galactosidase activity was identified. We determined that -galactosidase activity was due to BgaA, a surface protein in S. pneumoniae, and that the expression of bgaA was regulated. Transcription analyses demonstrated expression of bgaA in the constitutive -galactosidase (BgaA^C) mutant but not in the parent. -galactosidase expression was induced in the parent under specific growth conditions, however the levels did not reach those of the BgaA^C mutant. We localized the mutation resulting in the BgaA^C phenotype to a region upstream of bgaA and in the promoter of a phosphoenolpyruvate-dependent phosphotransferase system (PTS) operon. The mutation was in a cre and affected binding of CcpA (catabolite control protein A), a key regulator of many carbon metabolism genes. The pts operon and bgaA were co-transcribed, and their transcription was regulated by CcpA. Deletion of ccpA altered -galactosidase activity, leading to a 7-fold increase in the parent but a 5-fold decrease in the BgaA^C mutant. The resulting -galactosidase activities were the same in the two strains, suggesting the presence of a second repressor. The presence of glucose in the growth medium resulted in pts-bgaA repression by both CcpA and the second repressor, with the latter being important in responding to glucose concentration. Expression of -galactosidase is important for S. pneumoniae adherence during colonization of the nasopharynx, a site normally devoid of glucose. CcpA and environmental glucose concentrations thus appear to play important roles in the regulation of a niche-specific virulence factor.

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