Staphylococcus aureus
is a significant infectious threat to global public health. Acquisition or synthesis of heme is required for
S. aureus
to capture energy through respiration, but an excess of this critical cofactor is toxic to bacteria.
S. aureus
employs the heme sensor system (HssRS) to overcome heme toxicity; however, the mechanism of heme sensing is not defined. Here, we describe the identification of a small molecule activator of HssRS that induces endogenous heme biosynthesis by perturbing central metabolism. This molecule is toxic to fermenting
S. aureus
, including clinically relevant small colony variants. The utility of targeting fermenting bacteria is exemplified by the fact that this compound prevents the emergence of antibiotic resistance, enhances phagocyte killing, and reduces
S. aureus
pathogenesis. Not only is this small molecule a powerful tool for studying bacterial heme biosynthesis and central metabolism; it also establishes targeting of fermentation as a viable antibacterial strategy.
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.
SUMMARY
The rising problem of antimicrobial resistance in Staphylococcus aureus necessitates the discovery of novel therapeutic targets for small-molecule intervention. A major obstacle of drug discovery is identifying the target of molecules selected from high-throughput phenotypic assays. Here, we show that the toxicity of a small molecule termed ’882 is dependent on the constitutive activity of the S. aureus virulence regulator SaeRS, uncovering a link between virulence factor production and energy generation. A series of genetic, physiological, and biochemical analyses reveal that ’882 inhibits iron-sulfur (Fe-S) cluster assembly most likely through inhibition of the Suf complex, which synthesizes Fe-S clusters. In support of this, ’882 supplementation results in decreased activity of the Fe-S cluster-dependent enzyme aconitase. Further information regarding the effects of ’882 has deepened our understanding of virulence regulation and demonstrates the potential for small-molecule modulation of Fe-S cluster assembly in S. aureus and other pathogens.
Gram-positive bacteria cause the majority of skin and soft tissue infections (SSTIs), resulting in the most common reason for clinic visits in the United States. Recently, it was discovered that Gram-positive pathogens use a unique heme biosynthesis pathway, which implicates this pathway as a target for development of antibacterial therapies. We report here the identification of a small-molecule activator of coproporphyrinogen oxidase (CgoX) from Gram-positive bacteria, an enzyme essential for heme biosynthesis. Activation of CgoX induces accumulation of coproporphyrin III and leads to photosensitization of Gram-positive pathogens. In combination with light, CgoX activation reduces bacterial burden in murine models of SSTI. Thus, small-molecule activation of CgoX represents an effective strategy for the development of light-based antimicrobial therapies.
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