Conserved metabolic regulator ArcA responds to oxygen availability, iron limitation, and cell envelope perturbations during bacteremia

Abstract

ABSTRACT Gram-negative facultative anaerobes often cause bacteremia, a systemic infection associated with severe clinical outcomes. ArcAB, a two-component regulatory system that represses aerobic respiration, is a key mediator of metabolic adaptation for such bacteria. Using targeted mutational analysis informed by global genetic screens, we identified the arcA gene as promoting fitness of Citrobacter freundii, Klebsiella pneumoniae, and Serratia marcescens but not Escherichia coli in a murine model of bacteremia. arcA mutants exhibit a dysregulated response to changes in oxygen availability, iron limitation, and membrane perturbations, which bacterial cells experience during infection. The genetic response of the arcA mutants to the cationic antimicrobial peptide polymyxin B supports an expanded role for ArcA as an activator in response to membrane damage. ArcA function is linked to electron transport chain activity based on its response to proton motive force uncoupling by carbonylcyanide-m-chlorophenylhydrazone (CCCP). Differences in lactate, acetate, and lactate dehydrogenase activity between arcA mutant and wild-type cells following CCCP treatment support an ArcA-mediated shift to fermentation independent of oxygen availability. This study highlights the semi-conserved role of ArcA during bacteremia and consolidates infection phenotypes into a comprehensive model based on respiratory activity. IMPORTANCE Infections of the bloodstream are life-threatening and can result in sepsis. Gram-negative bacteria cause a significant portion of bloodstream infections, which is also referred to as bacteremia. The long-term goal of our work is to understand how such bacteria establish and maintain infection during bacteremia. We have previously identified the transcription factor ArcA, which promotes fermentation in bacteria, as a likely contributor to the growth and survival of bacteria in this environment. Here, we study ArcA in the Gram-negative species Citrobacter freundii, Klebsiella pneumoniae, and Serratia marcescens. Our findings aid in determining how these bacteria sense their environment, utilize nutrients, and generate energy while countering the host immune system. This information is critical for developing better models of infection to inform future therapeutic development.

Keywords

• bacteremia
• two-component regulatory systems
• metabolic regulation
• Gram-negative pathogenesis