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Journal of Bacteriology, November 2001, p. 6324-6334, Vol. 183, No. 21
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.21.6324-6334.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Regulation of D-Alanyl-Lipoteichoic Acid Biosynthesis in Streptococcus agalactiae Involves a Novel Two-Component Regulatory System

Claire Poyart,1,2 Marie Cécile Lamy,1 Claire Boumaila,1 Franz Fiedler,3 and Patrick Trieu-Cuot1,2,*

Laboratoire de Microbiologie, INSERM U-4111 and Laboratoire Mixte Pasteur-Necker de Recherche sur les Streptocoques et Streptococcies,2 Faculté de Médecine Necker-Enfants Malades, 75730 Paris Cedex 15, France, and Institute for Genetics and Microbiology, University of Munich, D-80638 Munich, Germany3

Received 16 April 2001/Accepted 8 August 2001

The dlt operon of gram-positive bacteria comprises four genes (dltA, dltB, dltC, and dltD) that catalyze the incorporation of D-alanine residues into the lipoteichoic acids (LTAs). In this work, we characterized the dlt operon of Streptococcus agalactiae, which, in addition to the dltA to dltD genes, included two regulatory genes, designated dltR and dltS, located upstream of dltA. The dltR gene encodes a 224-amino-acid putative response regulator belonging to the OmpR family of regulatory proteins. The dltS gene codes for a 395-amino-acid putative histidine kinase thought to be involved in the sensing of environmental signals. The dlt operon of S. agalactiae is mainly transcribed from the PdltR promoter, which directs synthesis of a 6.5-kb transcript encompassing dltR, dltS, dltA, dltB, dltC, and dltD, and from a weaker promoter, PdltA, which is located in the 3' extremity of dltS. We demonstrate that PdltR, but not PdlA, is activated by DltR in the presence of DltS in D-Ala-deficient LTA mutants resulting from insertional inactivation of the dltA gene, which encodes the cytoplasmic D-alanine-D-alanyl carrier ligase DltA. Expression of the dlt operon does not require DltR and DltS, since the basal activity of PdltR is high, being 20-fold that of the constitutive promoter PaphA-3 which directs synthesis of the kanamycin resistance gene aphA-3 in various gram-positive bacteria. We hypothesize that the role of DltR and DltS in the control of expression of the dlt operon is to maintain the level of D-Ala esters in LTAs at a constant and appropriate value whatever the environmental conditions. The DltA- mutant displayed the ability to form clumps in standing culture and exhibited an increased susceptibility to the cationic antimicrobial polypeptide colistin.


* Corresponding author. Mailing address: Laboratoire de Microbiologie, Faculté de Médecine Necker-Enfants Malades, 75730 Paris Cedex 15, France. Phone: (33)(1)40 61 56 79. Fax: (33)(1)40 61 55 92. E-mail: ptrieu{at}pasteur.fr.


Journal of Bacteriology, November 2001, p. 6324-6334, Vol. 183, No. 21
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.21.6324-6334.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.



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