RT Journal Article
SR Electronic
T1 Regulation of <span class="sc">d</span>-Alanyl-Lipoteichoic Acid Biosynthesis in <em>Streptococcus agalactiae</em> Involves a Novel Two-Component Regulatory System
JF Journal of Bacteriology
JO J. Bacteriol.
FD American Society for Microbiology
SP 6324
OP 6334
DO 10.1128/JB.183.21.6324-6334.2001
VO 183
IS 21
A1 Poyart, Claire
A1 Lamy, Marie Cécile
A1 Boumaila, Claire
A1 Fiedler, Franz
A1 Trieu-Cuot, Patrick
YR 2001
UL http://jb.asm.org/content/183/21/6324.abstract
AB 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 thedlt 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 ofS. 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 ofdltS. 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.