The Bacillus anthracis two-component system signaling response to host stressors.
Laut, Clare Lynn
In bacteria, stress-induced gene expression changes can occur via signal transduction systems known as two-component systems (TCSs). Bacillus anthracis, the causative agent of anthrax, encounters numerous stressors that aim to disarm the pathogen and reduce infectious burden. We hypothesized that B. anthracis adapts to toxic environments encountered during infection via TCSs. Here we investigated three TCSs encoded by B. anthracis. First, EdsRS (envelope disruption sensing) is activated by disruptions to the cellular barrier induced by the antimicrobial, targocil. Active EdsRS induces expression of a previously uncharacterized cardiolipin synthase. This results in an increase in cardiolipin levels, which restored B. anthracis envelope integrity. Next, HssRS (heme sensor system) responds to high heme levels, the iron-containing cofactor of hemoglobin that is encountered as B. anthracis grows to extreme densities in the blood. HssRS engages in cross-regulation with HitRS (HssRS interfacing TCS) which is activated by cell envelope stress. We confirmed HitRS regulated genes are induced within phagocytes using innovative imaging approaches and the eukaryotic factor responsible will be identified using an arrayed CRISPR/Cas9 library screen. HitRS is also required for viability in the presence of macrophages, indicating that both HssRS and HitRS are key in host derived conditions. To identify bacterial gene products involved in TCS stress-sensing, a genetic selection was designed. Highly conserved modulators of protein homeostasis were found to be required for HitRS and HssRS function. The substrate binding components of protein chaperones, DnaJ, and proteases, ClpX, are essential for the activation of HitRS and HssRS through maintenance of TCS protein levels. We hypothesize that coordination of the response to antibiotic compounds, envelope damage and heme stress must be tightly modulated at the protein level. This is required as B. anthracis transitions throughout various host niches and adapts to these dynamic conditions. The results of this work increased our understanding of how B. anthracis senses chemical or physical changes in the environment and regulates the response to cause infection.