Two-Component System Cross-Regulation Integrates Bacillus anthracis Response to Heme and Cell Envelope Stress

Abstract

Two-component signaling systems (TCSs) are one of the mechanisms that bacteria employ to sense and adapt to changes in the environment. A prototypical TCS functions as a phosphorelay from a membrane-bound sensor histidine kinase (HK) to a cytoplasmic response regulator (RR) that controls target gene expression. Despite significant homology in the signaling domains of HKs and RRs, TCSs are thought to typically function as linear systems with little to no cross-talk between non-cognate HK-RR pairs. Here we have identified several cell envelope acting compounds that stimulate a previously uncharacterized Bacillus anthracis TCS. Furthermore, this TCS cross-signals with the heme sensing TCS HssRS; therefore, we have named it HssRS interfacing TCS (HitRS). HssRS reciprocates cross-talk to HitRS, suggesting a link between heme toxicity and cell envelope stress. The signaling between HssRS and HitRS occurs in the parental B. anthracis strain; therefore, we classify HssRS-HitRS interactions as cross-regulation. Cross-talk between HssRS and HitRS occurs at both HK-RR and post-RR signaling junctions. Finally, HitRS also regulates a previously unstudied ABC transporter implicating this transporter in the response to cell envelope stress. This chemical biology approach to probing TCS signaling provides a new model for understanding how bacterial signaling networks are integrated to enable adaptation to complex environments such as those encountered during colonization of the vertebrate host.

The DNA glycosylase AlkD uses a non-base-flipping mechanism to excise bulky lesions

“…The 1-kb flanking regions surrounding alkD were inserted into the knockout-plasmid pLM4 using standard molecular biology techniques 41 . The modified plasmid was propagated in E. coli K1077 before introduction by electroporation into Bacillus anthracis Sterne cells 42,43 .…”

Heme Synthesis and Acquisition in Bacterial Pathogens

“…When the Hrt efflux pump is inactivated in both S. aureus and L. lactis , levels of intracellular heme increase, suggesting that heme is the substrate of HrtAB export [229,237]. In B. anthracis , an HssRS orthologue controls the expression of HrtAB and cross-talks with a second TCS that responds to cellular envelope stresses, further implicating membrane damage as a component of heme stress [238]. HrtAB is actively expressed during murine anthrax, suggesting that organisms that replicate in the bloodstream must tolerate heme toxicity [33].…”

Regulation of bacterial surface attachment by a network of sensory transduction proteins

“…There is good experimental support for the paradigm that TCS form insulated signaling systems, with little cross-regulation between noncognate kinases and responses regulators [19][20][21][22], though there are examples of branched TCS pathways in which sensor kinases signal to more than one regulator, or in which signals from multiple kinases converge on a single regulator (reviewed in [23,24]). Complex cellular processes including sporulation [25], stress responses [16,[26][27][28][29], biofilm formation [30], and cell cycle [31,32] are often controlled by multiple TCS in branched pathways. In this study, we have defined a regulatory system composed of multiple TCS proteins and transcription factors that regulates holdfast development in C. crescentus.…”