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Woods KE, Akhter S, Rodriguez B, Townsend KA, Smith N, Smith B, Wambua A, Craddock V, Abisado-Duque RG, Santa EE, Manson DE, Oakley BR, Hancock LE, Miao Y, Blackwell HE, Chandler JR. Characterization of natural product inhibitors of quorum sensing in Pseudomonas aeruginosa reveals competitive inhibition of RhlR by ortho-vanillin. bioRxiv 2024:2024.02.24.581676. [PMID: 38559250 PMCID: PMC10979890 DOI: 10.1101/2024.02.24.581676] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
Quorum sensing (QS) is a cell-cell signaling system that enables bacteria to coordinate population density-dependent changes in behavior. This chemical communication pathway is mediated by diffusible N-acyl L-homoserine lactone signals and cytoplasmic signal-responsive LuxR-type receptors in Gram-negative bacteria. As many common pathogenic bacteria use QS to regulate virulence, there is significant interest in disrupting QS as a potential therapeutic strategy. Prior studies have implicated the natural products salicylic acid, cinnamaldehyde and other related benzaldehyde derivatives as inhibitors of QS in the opportunistic pathogen Pseudomonas aeruginosa, yet we lack an understanding of the mechanisms by which these compounds function. Herein, we evaluate the activity of a set of benzaldehyde derivatives using heterologous reporters of the P. aeruginosa LasR and RhlR QS signal receptors. We find that most tested benzaldehyde derivatives can antagonize LasR or RhlR reporter activation at micromolar concentrations, although certain molecules also caused mild growth defects and nonspecific reporter antagonism. Notably, several compounds showed promising RhlR or LasR specific inhibitory activities over a range of concentrations below that causing toxicity. Ortho-Vanillin, a previously untested compound, was the most promising within this set. Competition experiments against the native ligands for LasR and RhlR revealed that ortho-vanillin can interact competitively with RhlR but not with LasR. Overall, these studies expand our understanding of benzaldehyde activities in the LasR and RhlR receptors and reveal potentially promising effects of ortho-vanillin as a small molecule QS modulator against RhlR.
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Affiliation(s)
- Kathryn E. Woods
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045
| | - Sana Akhter
- Center for Computational Biology, University of Kansas, Lawrence, KS 66045
| | - Blanca Rodriguez
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045
| | - Kade A. Townsend
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045
| | - Nathan Smith
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045
| | - Ben Smith
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045
| | - Alice Wambua
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045
| | - Vaughn Craddock
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045
| | | | - Emma E. Santa
- Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53706
| | - Daniel E. Manson
- Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53706
| | - Berl R. Oakley
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045
| | - Lynn E. Hancock
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045
| | - Yinglong Miao
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045
- Center for Computational Biology, University of Kansas, Lawrence, KS 66045
- Current location: Department of Pharmacology and Computational Medicine Program, University of North Carolina–Chapel Hill, Chapel Hill, NC 27599
| | - Helen E. Blackwell
- Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53706
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Abisado-Duque RG, Townsend KA, Mckee BM, Woods K, Koirala P, Holder AJ, Craddock VD, Cabeen M, Chandler JR. An Amino Acid Substitution in Elongation Factor EF-G1A Alters the Antibiotic Susceptibility of Pseudomonas aeruginosa LasR-Null Mutants. J Bacteriol 2023; 205:e0011423. [PMID: 37191503 PMCID: PMC10294626 DOI: 10.1128/jb.00114-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Accepted: 04/22/2023] [Indexed: 05/17/2023] Open
Abstract
The opportunistic bacterium Pseudomonas aeruginosa uses the LasR-I quorum-sensing system to increase resistance to the aminoglycoside antibiotic tobramycin. Paradoxically, lasR-null mutants are commonly isolated from chronic human infections treated with tobramycin, suggesting there may be a mechanism that permits the emergence of lasR-null mutants under tobramycin selection. We hypothesized that some other genetic mutations that emerge in these isolates might modulate the effects of lasR-null mutations on antibiotic resistance. To test this hypothesis, we inactivated lasR in several highly tobramycin-resistant isolates from long-term evolution experiments. In some of these isolates, inactivating lasR further increased resistance, compared with decreasing resistance of the wild-type ancestor. These strain-dependent effects were due to a G61A nucleotide polymorphism in the fusA1 gene encoding amino acid substitution A21T in the translation elongation factor EF-G1A. The EF-G1A mutational effects required the MexXY efflux pump and the MexXY regulator ArmZ. The fusA1 mutation also modulated ΔlasR mutant resistance to two other antibiotics, ciprofloxacin and ceftazidime. Our results identify a gene mutation that can reverse the direction of the antibiotic selection of lasR mutants, a phenomenon known as sign epistasis, and provide a possible explanation for the emergence of lasR-null mutants in clinical isolates. IMPORTANCE One of the most common mutations in Pseudomonas aeruginosa clinical isolates is in the quorum sensing lasR gene. In laboratory strains, lasR disruption decreases resistance to the clinical antibiotic tobramycin. To understand how lasR mutations emerge in tobramycin-treated patients, we mutated lasR in highly tobramycin-resistant laboratory strains and determined the effects on resistance. Disrupting lasR enhanced the resistance of some strains. These strains had a single amino acid substitution in the translation factor EF-G1A. The EF-G1A mutation reversed the selective effects of tobramycin on lasR mutants. These results illustrate how adaptive mutations can lead to the emergence of new traits in a population and are relevant to understanding how genetic diversity contributes to the progression of disease during chronic infections.
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Affiliation(s)
| | - Kade A. Townsend
- Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA
| | - Brielle M. Mckee
- Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA
| | - Kathryn Woods
- Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA
| | - Pratik Koirala
- Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA
| | - Alexandra J. Holder
- Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA
| | - Vaughn D. Craddock
- Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA
| | - Matthew Cabeen
- Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, Oklahoma, USA
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