Activation of the Listeria monocytogenes stressosome in the intracellular eukaryotic environment

• Published in: Applied and environmental microbiology 2021-05, Vol.87 (12), p.1-e0039721
• Main Authors: Dessaux, Charlotte, Pucciarelli, M Graciela, Guerreiro, Duarte N, O'Byrne, Conor P, García-Del Portillo, Francisco
• Format: Article
• Language: English
• Subjects: Bacteria; Core protein; Epithelial cells; Epithelium; Intracellular; Listeria; Listeria monocytogenes; Membrane proteins; Membranes; Oxidative stress; Phosphorylation; Physiology; Proteins; Sigma factor; Stress concentration
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.00397-21

is a ubiquitous environmental bacterium and intracellular pathogen that responds to stress using predominantly the alternative sigma factor SigB. Stress is sensed by a multiprotein complex, the stressosome, extensively studied in bacteria grown in nutrient media. Following signal perception, the stressosome triggers a phosphorylation cascade that releases SigB from its anti-sigma factor. Whether the stressosome is activated during the intracellular infection, is unknown. Here, we analysed the subcellular distribution of stressosome proteins in located inside epithelial cells following their immunodetection in membrane and cytosolic fractions prepared from intracellular bacteria. Unlike bacteria in laboratory media, intracellular bacteria have a large proportion of the core stressosome protein RsbR1 associated with the membrane. Another core protein, RsbS, is however undetectable. Despite the absence of RsbS, a SigB-dependent reporter revealed that SigB activity increases gradually from early (1 h) to late (6 h) post-infection times. We also found that RsbR1 paralogues attenuate the intensity of the SigB response and that the miniprotein Prli42, reported to tether the stressosome to the membrane in response to oxidative stress, plays no role in associating RsbR1 to the membrane of intracellular bacteria. Altogether, these data indicate that, once inside host cells, the stressosome may adopt a unique configuration to sense stress and to activate SigB in the intracellular eukaryotic niche. The response to stress mediated by the alternative sigma factor SigB has been extensively characterized in and These bacteria sense stress using a supra-macromolecular complex, the stressosome, which triggers a cascade that releases SigB from its anti-sigma factor. Despite much structural data of the complex available and analyses performed in mutants lacking components of the stressosome or the signalling cascade, the integration of the stress signal and the dynamics of stressosome proteins following environmental changes remain poorly understood. Our study provides data at the protein level on essential stressosome components and SigB activity when , normally a saprophytic bacterium, adapts to an intracellular lifestyle. Our results support activation of the stressosome complex in intracellular bacteria. The apparent loss of the stressosome core protein RsbS in intracellular also challenges current models, favouring the idea of a unique stressosome architecture responding