# Essential role of cytochrome bc1 in Pseudomonas aeruginosa cell physiology and virulence

## TL;DR

This study shows that cytochrome bc1 is crucial for the survival and virulence of Pseudomonas aeruginosa, a dangerous antibiotic-resistant bacteria.

## Contribution

The study reveals a new link between respiratory metabolism and virulence in Pseudomonas aeruginosa through cytochrome bc1.

## Key findings

- A bc1 deletion mutant shows significant growth defects in urinary- and lung-like media.
- The mutant has reduced virulence in bladder epithelial cells and is nearly avirulent in a mouse model.
- The mutant relies on alternative metabolic pathways, but with reduced ATP production.

## Abstract

Pseudomonas aeruginosa is a multidrug-resistant Gram-negative nosocomial pathogen posing a major healthcare burden due to its intrinsic antibiotic resistance and environmental adaptability, which continue to significantly constrain therapeutic options. This pathogen is a leading cause of hospital-acquired respiratory and urinary tract infections that are often persistent and difficult to treat. The elucidation of metabolic adaptations permitting P. aeruginosa survival and supporting virulence in diverse host environments is essential for informing novel treatments. This study investigates the role of cytochrome bc1 in P. aeruginosa PA14 growth, energetics, and virulence in vitro, under physiologically relevant conditions, and in vivo. The bc1 deletion mutant exhibits significant growth defects in urinary- and lung-like media, demonstrating its importance in PA14 physiology, and displays reduced virulence in bladder epithelial cell monolayers, mediated by decreased type III secretion system (T3SS) toxin expression. In vivo, the mutant was nearly avirulent in a murine systemic infection model. Bioenergetic analysis revealed severe decline in PA14 Δbc1 ATP production, aligning with the enzyme’s central role in respiration and providing a mechanistic explanation for the mutant’s reduced T3SS function, as toxin secretion requires energy. This work provides compelling evidence of direct T3SS regulation by cytochrome bc1, revealing a previously unrecognized link between respiratory metabolism and virulence. Metabolic profiling indicates that to compensate for cytochrome bc1 loss, the mutant relies on NDH-2 and bd oxidase, permitting cellular survival but substantially reducing ATP yield. Collectively, these findings establish cytochrome bc1 as a target for antibiotic development against P. aeruginosa, impacting bioenergetics, physiology, and virulence.