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The density of negative charge in the cell wall influences two-component signal transduction in Bacillus subtilis

Leena Valmu^3,

¹ Vaccine Development Laboratory, Department of Vaccine, National Public Health Institute, Mannerheimintie 166, FIN-00300 Helsinki, Finland
² Institut für Mikrobiologie und Molecularbiologie, Ernst-Moritz-Arndt-Universität Greifswald, F.-L.-Jahn-str. 15, D-17487 Greifswald, Germany
³ Institute of Biotechnology, University of Helsinki, Viikki Biocenter, PO Box 56, FIN-00014, University of Helsinki, Finland

CorrespondenceVesa P. Kontinen

Vesa.Kontinen{at}ktl.fi

The Dlt system modulates the density of negative charge in the cell wall of Gram-positive bacteria by substituting anionic polymers (wall and lipoteichoic acids) with D-alanine. The htrA and htrB genes, regulated by the CssRS two-component system (TCS) and encoding membrane-associated protein quality control proteases, were expressed at strongly decreased levels in a mutant with defective Dlt (dltD : : miniTn10) as compared to the dlt⁺ wild-type strain under a secretion stress condition (hypersecretion of AmyQ -amylase). The level of HtrA protein in the extracellular proteome of the dltD mutant was decreased consistently. Expression from the promoter of the liaIHGFSR (yvqIHGFEC) operon (P_liaI) is dependent on the LiaRS TCS. The Dlt defect increased the expression from P_liaI under two stress conditions, AmyQ hypersecretion and treatment with a cationic antimicrobial peptide (LL-37), but decreased the expression in vancomycin-treated cells. Furthermore, Dlt inactivation enhanced the expression of the YxdJK-regulated yxdL gene in LL-37-treated cells. The increased net negative charge of the cell wall seems to cause varied and opposite effects on the expression of CssRS-, LiaRS- and YxdJK-regulated genes under different stress conditions. The results suggest that TCSs which sense misfolded proteins or peptides are modulated by the density of negative charge in the cell wall. The density of negative charge on the outer surface of the cell membrane did not have a similar effect on TCSs.

Present Address: Finnish Red Cross Blood Service, Research and Development, Kivihaantie 7, FIN-00310, Helsinki, Finland.