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Journal of Bacteriology, September 2001, p. 5248-5256, Vol. 183, No. 18
Institut für Mikrobiologie,
Eidgenössische Technische Hochschule Zürich, 8092 Zürich, Switzerland,1 and
Institut für Biotechnologie 1, Forschungszentrum
Jülich, 52425 Jülich, Germany2
Received 17 January 2001/Accepted 4 June 2001
Klebsiella pneumoniae is able to grow anaerobically
with citrate as a sole carbon and energy source by a
fermentative pathway involving the Na+-dependent
citrate carrier CitS, citrate lyase, and oxaloacetate decarboxylase. The corresponding genes are organized in the
divergent citC and citS operons, whose
expression is strictly dependent on the citrate-sensing
CitA-CitB two-component system. Evidence is provided here that
the citrate fermentation genes are subject to catabolite repression,
since anaerobic cultivation with a mixture of citrate and glucose or
citrate and gluconate resulted in diauxic growth. Glucose, gluconate,
and also glycerol decreased the expression of a chromosomal
citS-lacZ fusion by 60 to 75%, whereas a direct inhibition of the citrate fermentation enzymes was not observed. The purified cyclic AMP (cAMP) receptor protein (CRP) of K.
pneumoniae bound to two sites in the
citC-citS intergenic region, which were centered at
position
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.18.5248-5256.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Catabolite Repression of the Citrate Fermentation
Genes in Klebsiella pneumoniae: Evidence for
Involvement of the Cyclic AMP Receptor Protein
41.5 upstream of the citC and
citS transcriptional start sites. Binding was apparently
stimulated by the response regulator CitB. These data indicate that
catabolite repression of the citrate fermentation genes is exerted by
CRP and that in the absence of repressing carbon sources the cAMP-CRP
complex serves to enhance the basal, CitB-dependent transcription level.
*
Corresponding author. Mailing address: Institut
für Biotechnologie 1, Forschungszentrum Jülich, 52425 Jülich, Germany. Phone: 49 2461 615515. Fax: 49 2461 612710. E-mail: m.bott{at}fz-juelich.de.
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