Conserved Metabolic Regulator ArcA Responds to Oxygen Availability, Iron Limitation, and Cell Envelope Perturbations during Bacteremia

Abstract

Bacteremia, a systemic infection associated with severe clinical outcomes, is often caused by Gram-negative facultative anaerobes. 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 thearcAgene as promoting fitness ofKlebsiella pneumoniae,Citrobacter freundii, andSerratia marcescensbut notEscherichia coliin a murine model of bacteremia. Engineered mutants lackingarcAexhibit a dysregulated response to changes in oxygen availability, iron limitation, and membrane perturbations, all of which bacterial cells experience during infection. The genetic response of thearcAmutants relative to wild-type strains to the cationic antimicrobial peptide polymyxin B demonstrates an expanded role for ArcA as an activator in response to membrane damage in addition to metabolic adaptation. ArcA function is furthermore linked to electron transport chain activity based on its response to uncoupling of proton motive force by carbonyl cyanide-m-chlorophenylhydrazone (CCCP). Differences in lactate and acetate levels as well as lactate dehydrogenase activity between arcA mutant and wild-type cells following CCCP treatment establish 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.

A novel method for integrating genomic and Tn-Seq data to identify commonin vivofitness mechanisms across multiple bacterial species

“…ArcA is a global gene regulator of aerobic respiration that contributes to the maintenance of a proton motive force when oxygen is available. In a recent study [119], we constructed deletion mutants in the aerobic respiration control sensor arcA across four species and confirmed that ArcA is a bacteremia-fitness factor in K. pneumoniae, C. freundii, and S. marcescens but not E. coli. ArcA is conserved across the Enterobacterales and clearly contributes to fitness in a murine bacteremia model [119].…”

“…In a recent study [119], we constructed deletion mutants in the aerobic respiration control sensor arcA across four species and confirmed that ArcA is a bacteremia-fitness factor in K. pneumoniae, C. freundii, and S. marcescens but not E. coli. ArcA is conserved across the Enterobacterales and clearly contributes to fitness in a murine bacteremia model [119]. Because this regulator, along with ArcB, mediates transition from aerobic to anaerobic growth, mutants in arcA do not grow well under anaerobic conditions.…”