The study looks at how changing the electric charge on the surface of a common bacteria (Bacillus subtilis) affects the bacteria’s internal stress‑sensing systems, especially when exposed to the antimicrobial peptide LL‑37. It shows that making the cell wall more negatively charged flips the activity of several signaling pathways, but this is a basic microbiology finding and doesn’t translate into any direct health or performance advice for people.

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 alpha-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.