C-type natriuretic peptide modulates quorum sensing molecule and toxin production in Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa coordinates its virulence expression and establishment in the host in response to modification of its environment. During the infectious process, bacteria are exposed to and can detect eukaryotic products including hormones. It has been shown that P. aeruginosa is sensitive to natriuretic peptides, a family of eukaryotic hormones, through a cyclic nucleotide-dependent sensor system that modulates its cytotoxicity. We observed that pre-treatment of P. aeruginosa PAO1 with C-type natriuretic peptide (CNP) increases the capacity of the bacteria to kill Caenorhabditis elegans through diffusive toxin production. In contrast, brain natriuretic peptide (BNP) did not affect the capacity of the bacteria to kill C. elegans. The bacterial production of hydrogen cyanide (HCN) was enhanced by both BNP and CNP whereas the production of phenazine pyocyanin was strongly inhibited by CNP. The amount of 2-heptyl-4-quinolone (HHQ), a precursor to 2-heptyl-3-hydroxyl-4-quinolone (Pseudomonas quinolone signal; PQS), decreased after CNP treatment. The quantity of 2-nonyl-4-quinolone (HNQ), another quinolone which is synthesized from HHQ, was also reduced after CNP treatment. Conversely, both BNP and CNP significantly enhanced bacterial production of acylhomoserine lactone (AHL) [e.g. 3-oxo-dodecanoyl-homoserine lactone (3OC12-HSL) and butanoylhomoserine lactone (C4-HSL)]. These results correlate with an induction of lasI transcription 1 h after bacterial exposure to BNP or CNP. Concurrently, pre-treatment of P. aeruginosa PAO1 with either BNP or CNP enhanced PAO1 exotoxin A production, via a higher toxA mRNA level. At the same time, CNP led to elevated amounts of algC mRNA, indicating that algC is involved in C. elegans killing. Finally, we observed that in PAO1, Vfr protein is essential to the pro-virulent effect of CNP whereas the regulator PtxR supports only a part of the CNP pro-virulent activity. Taken together, these data reinforce the hypothesis that during infection natriuretic peptides, particularly CNP, could enhance the virulence of PAO1. This activity is relayed by Vfr and PtxR activation, and a general diagram of the virulence activation cascade involving AHL, HCN and exotoxin A is proposed.

The aliphatic amidase AmiE is involved in regulation of Pseudomonas aeruginosa virulence

“…Our previous study showing that the hormone CNP is able to bind AmiC triggering thus both ami operon transcription and an enhancement of the bacterial virulence16 could not directly fit with our present data showing that AmiE, when over-produced, negatively controls virulence in P. aeruginosa . Next to the direct control of amiE transcription by the AmiC/AmiR sensor/regulator pair, it has been shown that the amiE gene translation is under the Crc/Hfq proteins control49.…”

“…In previous studies, we showed that the opportunistic pathogen P. aeruginosa is able to sense the human C-type natriuretic peptide (CNP), which leads to modifying its biofilm formation1216. This responsiveness of P. aeruginosa to this human hormone is relayed by the specific bacterial sensor protein AmiC, which displays a structural and pharmacological profile identical to the human natriuretic receptor subtype C (hNPR-C)12.…”

“…We have previously shown that CNP slightly enhances the bacterial virulence16 through ami operon transcription12. Because CNP triggers AmiR release after binding to AmiC sensor, it is tempting to speculate that the transcription anti-termination factor AmiR could regulate other targets involved in virulence promotion and biofilm repression, conferring to the sensor AmiC protein, in association with its AmiR partner new functions.…”

“…Recently, it has been shown that the human hormone CNP acts as an AmiC agonist, which activates the transcription of the whole ami operon, including the gene for the AmiE aliphatic enzyme12. Since CNP is able to modify P. aeruginosa virulence16 and biofilm formation12, we hypothesized that the final product of the ami operon, i.e. the AmiE enzyme, could be involved in balancing biofilm formation and bacterial virulence.…”

Host Peptidic Hormones Affecting Bacterial Biofilm Formation and Virulence

“…The provirulent effect of CNP on P. aeruginosa was shown to result from the increase in the cAMP concentration [37], which activates the virulence factor regulator Vfr [71] (Fig. 1).…”