Bacillus anthracis Responds to Targocil-Induced Envelope Damage through EdsRS Activation of Cardiolipin Synthesis

Abstract

Bacillus anthracis is a spore-forming bacterium that causes devastating infections and has been used as a bioterror agent. This pathogen can survive hostile environments through the signaling activity of two-component systems, which couple environmental sensing with transcriptional activation to initiate a coordinated response to stress. In this work, we describe the identification of a two-component system, EdsRS, which mediates the B. anthracis response to the antimicrobial compound targocil. Targocil is a cell envelope-targeting compound that is toxic to B. anthracis at high concentrations. Exposure to targocil causes damage to the cellular barrier and activates EdsRS to induce expression of a previously uncharacterized cardiolipin synthase, which we have named ClsT. Both EdsRS and ClsT are required for protection against targocil-dependent damage. Induction of clsT by EdsRS during targocil treatment results in an increase in cardiolipin levels, which protects B. anthracis from envelope damage. Together, these results reveal that a two-component system signaling response to an envelope-targeting antimicrobial induces production of a phospholipid associated with stabilization of the membrane. Cardiolipin is then used to repair envelope damage and promote B. anthracis viability. IMPORTANCE Compromising the integrity of the bacterial cell barrier is a common action of antimicrobials. Targocil is an antimicrobial that is active against the bacterial envelope. We hypothesized that Bacillus anthracis, a potential weapon of bioterror, senses and responds to targocil to alleviate targocil-dependent cell damage. Here, we show that targocil treatment increases the permeability of the cellular envelope and is particularly toxic to B. anthracis spores during outgrowth. In vegetative cells, two-component system signaling through EdsRS is activated by targocil. This results in an increase in the production of cardiolipin via a cardiolipin synthase, ClsT, which restores the loss of barrier function, thereby reducing the effectiveness of targocil. By elucidating the B. anthracis response to targocil, we have uncovered an intrinsic mechanism that this pathogen employs to resist toxicity and have revealed therapeutic targets that are important for bacterial defense against structural damage.

Mini Review: Bacterial Membrane Composition and Its Modulation in Response to Stress

“…In S. aureus , surface membrane charge is modified by the induction of mprF by the GraRS TCS, thereby increasing LPG levels ( Falord et al, 2011 ; Yang et al, 2012 ). In B. anthracis , the membrane-active compound targocil activates the EdsRS TCS, which induces expression of a cardiolipin synthase ( Laut et al, 2020 ). Thus, many different stimuli can trigger changes in the membrane lipidome.…”

Functional Analyses of the Bacillus velezensis HMB26553 Genome Provide Evidence That Its Genes Are Potentially Related to the Promotion of Plant Growth and Prevention of Cotton Rhizoctonia Damping-Off

“…Surfactin exhibited antibacterial, antiviral, antitumor and hemolytic action [44]. Plantazolicin damages the bacterial bilayer by entering the bacteria envelope and interfering with the membrane potential [45]. Butirosin A was a member of the second class of aminoglycoside antibiotics possessing a 2-deoxystreptamine aminocyclitol core [46].…”

Directed evolution reveals the mechanism of HitRS signal transduction inBacillus anthracis

“…anthracis encodes approximately 45 TCSs, reflecting the complex environmental conditions encountered by this pathogen. A few B. anthracis TCSs have been studied (Laut et al, 2020;Mike et al, 2014;Stauff & Skaar, 2009), including a heme sensor system (HssRS) that responds to changes in available heme and activates the expression of a heme efflux pump upon heme exposure, and a HssRS interfacing TCS (HitRS) that senses cell envelope stress and activates an uncharacterized transporter system (HitP) (Mike et al, 2014;Stauff & Skaar, 2009). Although the nature of the activating signal of HitRS remains unclear, a high-throughput screen identified a series of cell-envelope acting compounds as inducers of HitRS (Mike et al, 2014;Mike et al, 2013), including the small synthetic compound VU0120205 ('205) (Mike et al, 2013), nordihydroguaiaretic acid, which is an antioxidant that possesses activity against the cell membrane (Ooi et al, 2015), chlorpromazine, which is an antipsychotic drug that inhibits cell wall biogenesis (Klubes et al, 1971), targocil, which is an antibiotic that inhibits wall teichoic acid synthesis (Lee et al, 2010), and vancomycin, which inhibits Gram-positive cell wall biosynthesis and disrupts membrane integrity at low concentrations (Watanakunakorn, 1984).…”