PorA, a conserved C-terminal domain-containing protein, impacts the PorXY-SigP signaling of the type IX secretion system

AbstractPorphyromonas gingivalis, a periodontal pathogen, translocates many virulence factors including the cysteine proteases referred to as gingipains to the cell surface via the type IX secretion system (T9SS). Expression of the T9SS component proteins is regulated by the tandem signaling of the PorXY two-component system and the ECF sigma factor SigP. However, the details of this regulatory pathway are still unknown. We found that one of the T9SS conserved C-terminal domain-containing proteins, PGN_0123, which we have designated PorA, is involved in regulating expression of genes encoding T9SS structural proteins and that PorA can be translocated onto the cell surface without the T9SS translocation machinery. X-ray crystallography revealed that PorA has a domain similar to the mannose-binding domain of Escherichia coli FimH, the tip protein of Type 1 pilus. Mutations in the cytoplasmic domain of the sensor kinase PorY conferred phenotypic recovery on the ΔporA mutant. The SigP sigma factor, which is activated by the PorXY two-component system, markedly decreased in the ΔporA mutant. These results strongly support a potential role for PorA in relaying a signal from the cell surface to the PorXY-SigP signaling pathway.

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Carbon starvation induces the expression of PprB-regulated genes inPesudomonas aeruginosa

10.1101/639112 ◽

2019 ◽

Author(s):

Congcong Wang ◽

Wenhui Chen ◽

Aiguo Xia ◽

Rongrong Zhang ◽

Yajia Huang ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Cell Surface ◽

Biofilm Formation ◽

Carbon Starvation ◽

Secretion System ◽

Starvation Stress ◽

Two Component System ◽

Component System ◽

Two Component ◽

Cell Cell

ABSTRACTPseudomonas aeruginosacan cause severe infections in humans. This bacteria often adopt a biofilm lifestyle that is hard to treat. In several previous studies, the PprA-PprB two-component system (TCS), which controls the expression of type IVb pili, BapA adhesin, and CupE fimbriae, was shown to be involved in biofilm formation. However, signals or environmental conditions that can trigger the PprA-PprB TCS are still unknown, and the molecular mechanisms of PprB-mediated biofilm formation are poorly characterized. Here we report that carbon starvation stress (CCS) can induce the expression ofpprBand genes in the PprB regulon. The stress response sigma factor RpoS, rather than the two-component sensor PprA, was determined to mediate the induction ofpprBtranscription. We also observed a strong negative regulation of PprB to the transcription of itself. Further experiments showed that PprB overexpression greatly enhanced cell-cell adhesion (CCA) and cell-surface adhesion (CSA) inP. aeruginosa. Specially, under the background of PprB overexpression, both of the BapA adhesin and CupE fimbriae displayed positive effect on CCA and CSA, while the type IVb pili showed an unexpected negative effect on CCA and no effect on CSA. In addition, expression of the PprB regulon genes displayed significant increases in 3-day colony biofilms, indicating a possible carbon limitation state in these biofilms. The CSS-RpoS-PprB-Bap/Flp/CupE/Tad pathway identified in this study provides a new perspective on the process of biofilm formation under carbon-limited environments.IMPORTANCETypically, determining the external signals that can trigger a regulatory system is crucial to understand the regulatory logic and inward function of that system. The PprA-PprB two-component system was reported to be involved in biofilm formation inPseudomonas aeruginosa, but the signals that can trigger this system are unknown. In this study, we found that carbon starvation stress (CSS) can induce the transcription ofpprBand genes in PprB regulon, through an RpoS dependent pathway. Increase of PprB expression leads to enhanced cell-cell and cell-surface adhesions inP. aeruginosa,both of which are dependent mainly on the Bap adhesin secretion system and partially on the CupE fimbriae. Our findings suggest that PprB reinforces the structure of biofilms under carbon-limited conditions, and the Bap secretion system and CupE fimbriae are two potential targets for biofilm treatment.

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