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An SPFH Protein Couples Membrane Stress to Differentiation in Bacillus subtilis

ABSTRACT: Bacillus subtilis adapts to fluctuating environmental stress, such as membrane perturbation or alkaline conditions, using membrane-associated regulatory complexes. Here, we rename the previously termed pspA-ydjGHI operon to pspA-samGHI (for starvation and motility) to reflect its functional roles in membrane envelope stress signalling. The SamG–SamH membrane proteins recruit SamI, a cytosolic SPFH protein, which stabilizes focal membrane localization and recruitment of PspA, an ESCRT-III homolog. Under normal conditions, this system transiently assembles at the membrane, stabilizing it and allowing proper motility, secretion, and biofilm formation. Loss of SamI (ΔsamI/ΔydjI) leads to unbalanced SamG–SamH activity leading to a constitutive stress signalling, and global transcriptional changes reminiscent of starvation situations. This, in turn, blocks secretion of the matrix protein BslA, preventing biofilm formation, and reducing motility. Deletion of samH in combination with ΔsamI restores biofilm formation, while ΔpspA mutants form biofilms normally, indicating that PspA is dispensable for the developmental phenotype. Our findings reveal that beside membrane integrity SamGHI coordinates transcriptional homeostasis and multicellular development through formation of a membrane integral stress sensor complex.

ORGANISM(S): Bacillus subtilis subsp. subtilis str. 168

PROVIDER: GSE327651 | GEO | 2026/04/20

REPOSITORIES: GEO

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Project description:P. aeruginosa is the leading cause of death in patients with cystic fibrosis patients and one of the most problematic bacterial pathogens responsible for hospital-acquired infections. This pathogen has a high capacity to form biofilms on inert and living surfaces. This lifestyle allows it to persist in various hospital niches or on medical device which become vectors of contamination. Chronic infections are extremely complicated to eradicate due to the remarkable antimicrobial resistance of biofilms leading to a persistence in the tissue and an immune system exhaustion. It is therefore becoming essential to understand the mechanisms of biofilm formation to find new therapeutic targets in order to develop effective antibiofilm strategies. We previously identified in P. aeruginosa PA01 biofilms an accumulation of a hypothetical protein named PA3731 and its deletion impacted the biofilm formation. Similarly, to PspA, a protein from the well-known Psp system of E. coli, PA3731 is a has a predicted structure mostly helical, a PspA/IM30 domain and was accumulated during an osmotic shock. In P. aeruginosa genome, PA3731 appears to form a cluster with 3 genes (PA3732 to PA3729) that we named BAC system for “Biofilm Associated Cluster”. Here we worked on the PA14 strain and focus our study on PA14_16140, the PA3732 homologue. Using a ∆16140 mutant and phenotypic approach, we confirmed the role of the BAC system in the virulence and biofilm formation. We added supplementary genes coding the BAC system and demonstrate that altogether they form an operonic structure regulates by RpoN. We get further insight the role PA14_16140 by proteomic quantitative approach revealing an accumulation of the BAC system proteins in ∆16140 biofilms suggesting its regulatory role of the bac operon. Moreover, we present here the first crystallographic structure of PA14_16140. To summarise, according to our studies, and although further analysis is still required, this newly discovered operon appears composed firstly of its regulator and then of a homologous PspA.

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An SPFH Protein Couples Membrane Stress to Differentiation in Bacillus subtilis

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