Antagonistic self-sensing and mate-sensing signaling controls antibiotic-resistance transfer

Abstract

Conjugation is one of the most common ways bacteria acquire antibiotic resistance, contributing to the emergence of multidrugresistant "superbugs." Bacteria of the genus Enterococcus faecalis are highly antibiotic-resistant nosocomial pathogens that use the mechanism of conjugation to spread antibiotic resistance between resistance-bearing donor cells and resistance-deficient recipient cells. Here, we report a unique quorum sensing-based communication system that uses two antagonistic signaling molecules to regulate conjugative transfer of tetracycline-resistance plasmid pCF10 in E. faecalis. A "mate-sensing" peptide sex pheromone produced by recipient cells is detected by donor cells to induce conjugative genetic transfer. Using mathematical modeling and experimentation, we show that a second antagonistic "self-sensing" signaling peptide, previously known to suppress self-induction of donor cells, also serves as a classic quorum-sensing signal for donors that functions to reduce antibiotic-resistance transfer at high donor density. This unique form of quorum sensing may provide a means of limiting the spread of the plasmid and present opportunities to control antibiotic-resistance transfer through manipulation of intercellular signaling, with implications in the clinical setting.

Examination of Enterococcus faecalis Toxin-Antitoxin System Toxin Fst Function Utilizing a Pheromone-Inducible Expression Vector with Tight Repression and Broad Dynamic Range

“…In this report, we describe the construction and use of the pCIE Escherichia coli-E. faecalis shuttle/expression vector that uses the P Q cCF10 pheromone-responsive promoter from the plasmid pCF10 (24,25) for regulated transcription of cloned genes. Utilizing promoterless versions of the RNA I pAD1 and RNA I EF0409 genes, we demonstrated that this promoter (i) is tightly repressed in the absence of exogenous cCF10, (ii) is sensitive to added cCF10 at nanogram-per-milliliter concentrations, and (iii) possesses a large dynamic range.…”

Enterococcal Sex Pheromones: Evolutionary Pathways to Complex, Two-Signal Systems

“…The system not only avoids spurious induction but also limits the duration of induction due to the fact that the induction process itself dramatically increases inhibitor production, leading to rapid shut off of the response after a short period of induction (64). Furthermore, the inhibitor can function as a classic quorum sensor of donor density; at high donor densities, donors are poorly induced even by high concentrations of C (64). These cumulative effects of the inhibitor apparently limit the extent of induction in mixed populations of donors and recipients.…”

“…II shows how the system became more complex as it acquired the ability to enable its host cell to recognize C as an indicator of close proximity of plasmid-free recipients (mate sensing). At the mechanistic level, the C peptide competes with I, which functions as a classic quorum-sensing signal of donor density (self-sensing) (64). Evolution of the ability to differentially respond to these two antagonistic peptides was accompanied by the acquisition of genes encoding an oligopeptide binding protein, PrgZ, which binds both C and I with high affinity and increases their import via the Opp ABC transporter (37,38), and PrgY, a predicted membrane peptidase that reduces the production of endogenous C by the host cell (36).…”

cis-Antisense RNA and Transcriptional Interference: Coupled Layers of Gene Regulation

“…With exception of few studies [32,69,78,79], the presence of truncated RNA has not yet been vigorously investigated in systems with antisense transcription. The plethora of cis-antisense noncoding RNAs found in bacteria could potentially be the wreckage of RNAP collision due to transcription from conditionally activated hidden promoters, thus hinting that this could be rather a ubiquitous phenomenon.…”

“…Since antisense transcription can amplify the gap between transcript expression between two physiologically different states, such a gene regulatory mechanism is capable of showing reciprocal switch like behaviors such as bistable switch response in prgQ/prgX operon of E. faecalis [32,79,80] and scbA/scbR operon of S. coelicolor [69]. Antisense transcription from the prgQ/prgX locus of conjugative plasmid pCF10 of E. faecalis, allows for controlling the expression of long prgQ mRNA, which induces expression of downstream conjugationcausing genes.…”