Impact of either Elevated or Decreased Levels of Cytochrome bd Expression on Shigella flexneri Virulence

Abstract

Shigella spp. are the major cause of bacillary dysentery worldwide. The pathogenic process involves bacterial invasion and lysis of the phagocytic vacuole, followed by replication and movement within the cell cytoplasm and, ultimately, spread directly into adjacent cells. This study demonstrates that S. flexneri cytochrome bd expression is necessary for normal intracellular survival and virulence. Cytochrome bdis one of two terminal oxidases in the bacterial respiratory chain that reduce molecular oxygen to water, utilizing intermediates shuttled through the electron transport chain. S. flexneri mutants that contain a disruption in the cydC locus, which leads to defective cytochrome bd expression, or in the riboflavin (ribE) or ubiquinol-8 (ubiH) biosynthetic pathway, which leads to elevated cytochrome bd expression, were evaluated in intracellular survival and virulence assays. ThecydC mutant formed significantly smaller plaques, had significantly decreased intracellular survival, and had a 100-fold increase in lethal dose for mice compared with the wild type. TheribE and ubiH mutants each formed significantly larger plaques and had a 10-fold decrease in lethal dose for mice compared with the wild type. The data indicate that expression of cytochrome bd is required for S. flexneriintracellular survival and virulence.

Macrophage adaptation leads to parallel evolution of genetically diverse Escherichia coli small‐colony variants with increased fitness in vivo and antibiotic collateral sensitivity

“…Mutations in genes of the ETC are often associated with SCVs, however the diversity of mutational targets that can give rise to such SCVs is poorly understood. Our results (Table S2) & Goldberg, 1999). We confirmed this result in our SCV clone, by demonstrating that (i) ubiH expression was strongly reduced in the pepP mutant (clone 41; Fig.…”

A system for identifying post‐invasion functions of invasion genes: requirements for the Mxi–Spa type III secretion pathway of Shigella flexneri in intercellular dissemination

“…A MxiG derivative in which an internal RGD motif is replaced by RAD can secrete the Ipas and is invasive, but is unable to mediate proper bacterial contact with the protrusion membrane and, as such, forms abnormally small plaques. Other mutations that affect cell-to-cell spread include those that speci®cally inhibit intracellular septation (MacSõ Âomo  in et al, 1996), alter cytochrome bd expression (Way et al, 1999), destabilize the cytoplasmic membrane or peptidoglycan layer (Hong et al, 1998) or prevent periplasmic oxidative protein folding (Yu, 1998). No experiments have yet been reported that speci®cally implicate Ipa secretion in any post-invasion functions within epithelial cell or epithelial cell-like lines.…”

Cytochrome bd oxidase and nitric oxide: From reaction mechanisms to bacterial physiology

“…Finally, E. coli cytochrome bd-I was proved to provide the oxidizing power required both by the DsbA-DsbB system to catalyze disulfide bond formation during protein folding [91] and by protoporphyrinogen IX oxidase (HemG), an enzyme involved in heme biosynthesis [92]. It is worth mentioning that the expression of cytochrome bd oxidases was documented in a number of bacterial pathogens, such as Salmonella [7,10], Mycobacterium tuberculosis [12], Shigella flexneri [8], Streptococcus [13], Listeria monocytogenes [15], Brucella [9,14], members of the strict anaerobe Bacteroides class [11], Klebsiella pneumoniae [6], and for some of these pathogens a correlation between enzyme levels and virulence was observed. Particularly interesting is the case of Mycobacterium tuberculosis in which a transient up-regulation of cytochrome bd was observed in vivo in the transition from acute to chronic infection of mouse lungs, along with a reduced virulence of a mutant strain defective in the cytochrome bd-associated transporter CydC [12].…”

“…Beyond its role in energy metabolism, a large body of evidence suggests that the enzyme plays alternative functions relevant to physiology and, more specifically, to bacterial adaptation to a wide variety of stress conditions [3,5]. This respiratory oxidase has been identified in a number of pathogens [6][7][8][9][10][11][12][13][14][15] and, in some cases, its expression level was intriguingly found to positively correlate with virulence. Evidence suggests that cytochrome bd is implicated in adaptation to the hostile conditions created by host immunity during the infection process, though the molecular mechanism(s) through which the enzyme operates to enhance bacterial resistance have been only partly clarified.…”