Abstract
Bacteria have evolved numerous pathways to sense and respond to changing environmental conditions, including, within Gram-positive bacteria, the stressosome complex that regulates transcription of general stress response genes. However, the signalling molecules recognized by Gram-positive stressosomes have yet to be identified, hindering our understanding of the signal transduction mechanism within the complex. Furthermore, an analogous pathway has yet to be described in Gram-negative bacteria. Here we characterize a putative stressosome from the Gram-negative bacterium Vibrio brasiliensis. The sensor protein RsbR binds haem and exhibits ligand-dependent control of the stressosome complex activity. Oxygen binding to the haem decreases activity, while ferrous RsbR results in increased activity, suggesting that the V. brasiliensis stressosome may be activated when the bacterium enters anaerobic growth conditions. The findings provide a model system for investigating ligand-dependent signalling within stressosome complexes, as well as insights into potential pathways controlled by oxygen-dependent signalling within Vibrio species.
Highlights
Bacteria have evolved numerous pathways to sense and respond to changing environmental conditions, including, within Gram-positive bacteria, the stressosome complex that regulates transcription of general stress response genes
Stressosome-dependent signalling within Vibrio species likely involves the putative downstream phosphatase RsbU, which is a downstream protein in B. subtilis stressosome signalling and is localized in the V. brasiliensis genome with RsbR, RsbS and RsbT
Gramnegative bacteria, including Vibrio species, do not have sB, the protein required for initiating transcription of general stress response genes in B. subtilis[53]
Summary
Bacteria have evolved numerous pathways to sense and respond to changing environmental conditions, including, within Gram-positive bacteria, the stressosome complex that regulates transcription of general stress response genes. While a stressosome signalling complex from Gram-negative bacteria has yet to be characterized, these results suggest that a stressosome-like pathway may be involved in stress responses in Vibrio species. On the basis of homology with other globin coupled sensors, the N-terminal domain of RsbR in Vibrio brasiliensis maintains the proximal histidine residue required for haem binding, and the distal tyrosine involved in stabilization of bound ligands are conserved[25,26,27] Those key residues are not conserved in previously characterized RsbR proteins from B. subtilis and other Gram-positive bacteria[25]. We report the first example, to our knowledge, of a functional stressosome from a Gram-negative bacterium that senses O2 through a haem-bound RsbR
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