The absence of SigX results in impaired carbon metabolism and membrane fluidity in Pseudomonas aeruginosa

Abstract

In Pseudomonas aeruginosa, SigX is an extra-cytoplasmic function σ factor that belongs to the cell wall stress response network. In previous studies, we made the puzzling observation that sigX mutant growth was severely affected in rich lysogeny broth (LB) but not in minimal medium. Here, through comparative transcriptomic and proteomic analysis, we show that the absence of SigX results in dysregulation of genes, whose products are mainly involved in transport, carbon and energy metabolisms. Production of most of these genes is controlled by carbon catabolite repression (CCR), a key regulatory system than ensures preferential carbon source uptake and utilization, substrate prioritization and metabolism. The strong CCR response elicited in LB was lowered in a sigX mutant, suggesting altered nutrient uptake. Since the absence of SigX affects membrane composition and fluidity, we suspected membrane changes to cause such phenotype. The detergent polysorbate 80 (PS80) can moderately destabilize the envelope resulting in non-specific increased nutrient intake. Remarkably, growth, membrane fluidity and expression of dysregulated genes in the sigX mutant strain were restored in LB supplemented with PS80. Altogether, these data suggest that SigX is indirectly involved in CCR regulation, possibly via its effects on membrane integrity and fluidity.

Membrane-Interactive Compounds fromPistacia lentiscusL. ThwartPseudomonas aeruginosaVirulence

“…Interestingly, these results mirror those observed in P. aeruginosa sigX mutant and over-expressing strains when compared to the wild-type strain. 11,15,16 Moreover, Δ sigX cells display reduced membrane fluidity (membrane rigidification), HAQs QS-molecules production, pyocyanin pigment production, and virulence towards a C. elegans model. 9,16 Overall, these data provide evidences that PLFE1 most likely contain membrane-interactive compounds, as it is the case for many plant extracts.…”

“…11,15,16 Moreover, Δ sigX cells display reduced membrane fluidity (membrane rigidification), HAQs QS-molecules production, pyocyanin pigment production, and virulence towards a C. elegans model. 9,16 Overall, these data provide evidences that PLFE1 most likely contain membrane-interactive compounds, as it is the case for many plant extracts. 32,33 PLFE1 interaction with membrane lipid bilayers seems to be involved in the increased membrane stiffness, which might trigger the modulation of the ECFσ SigX.…”

“…Fluorescence anisotropy analysis of P. aeruginosa cells were performed as previously described. 16 Briefly, cell pellets of P. aeruginosa H103 untreated (control DMSO 1%) and treated by 100, 50, 25, 12.5, 6.25, 3.12, 1.6 and 0.8 μg mL −1 of PLFE1 were washed two times (7500 × g, 5 min, 25 °C) in 0.01 M MgSO 4 and resuspended in the same wash solution to reach an OD 580nm of 0.1. One μL of a 4 mM of 1,6-diphenyl-1,3,5-hexatriene (DPH) stock solution (Sigma-Aldrich) in tetrahydrofuran was added to 1 mL aliquot of the resuspended cultures and incubated in the dark for 30 min at 37 °C to allow the probe to incorporate into the cytoplasmic membrane.…”

“…9,11,13 More importantly, SigX has been reported to be involved in the regulation of fatty acid biosynthesis, which triggers changes in cell membrane phospholipid composition that affect membrane fluidity and envelope integrity. 11,14–16 SigX is also involved in physiological processes as important as iron uptake, virulence, motility, attachment, biofilm formation, and antibiotic resistance and susceptibility via direct and/or indirect governance. 9–11,17…”

Diversity of extracytoplasmic function sigma (σECF) factor‐dependent signaling in Pseudomonas

“…This σ ECF factor is homologous to σ SigX of the Gram‐positive bacterium Bacillus subtilis , which regulates membrane fluidity rendering B. subtilis more resistant to antimicrobial peptides (Cao and Helmann, ). In P. aeruginosa , σ SigX has a similar function and absence of this σ factor affects membrane fluidity, fatty acid composition of the cell membrane and cell morphology (Duchesne et al , ; Boechat et al , ; Blanka et al , ; Flechard et al , ). Several conditions that produce cell wall stress increase sigX expression and activity and, in response, σ SigX modulates expression of about 300 genes to relief the stress, including sigX itself (Bouffartigues et al , ; Gicquel et al , ; Blanka et al , ; Bouffartigues et al , ; Chevalier et al , 2019).…”