• Molecules and Cells
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• v.28 no.5
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• pp.447-453
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• 2009

The quorum sensing (QS) inhibitors that antagonize TraR, a receptor protein for N-3-oxo-octanoyl-L-homoserine lactones (3-oxo-C8-HSL), a QS signal of Agrobacterium tumefaciens were developed. The structural analogues of 3-oxo-C8-HSL were designed by in silico molecular modeling using SYBYL packages, and synthesized by the solid phase organic synthesis (SPOS) method, where the carboxamide bond of 3-oxo-C8-HSL was replaced with a nicotinamide or a sulfonamide bond to make derivatives of N-nicotinyl-L-homoserine lactones or N-sulfonyl-L-homoserine lactones. The in vivo inhibitory activities of these compounds against QS signaling were assayed using reporter systems and compared with the estimated binding energies from the modeling study. This comparison showed fairly good correlation, suggesting that the in silico interpretation of ligand-receptor structures can be a valuable tool for the pre-design of better competitive inhibitors. In addition, these inhibitors also showed anti-biofilm activities against Pseudomonas aeruginosa.

• Membrane and Water Treatment
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• v.14 no.1
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• pp.35-45
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• 2023

Biofilms significantly affect the performance of wastewater treatment processes in which biodegradability of numerous microorganisms are actively involved, and various technologies have been applied to secure microbial biofilms. Understanding changes in biofilm characteristics by regulating expression of signaling molecules is important to control and regulate biofilms in membrane bioreactor, i.e., biofouling. This study investigated effects of addition of acyl-homoserine lactones (AHL) as a controllable factor for the microbial signaling system on biofilm formation of Pseudomonas aeruginosa PAO1 and multiple strains in membrane bioreactor. The addition of three AHL, i.e., C4-, C6-, and C8-HSL, at a concentration of 200 ㎍/L, enhanced the formation of the PAO1 biofilm and the degree of increases in the biofilm formation of PAO1 were 70.2%, 76.6%, and 72.9%, respectively. The improvement of biofilm formation of individual strains by C4-HSL was an average of 68%, and the microbial consortia increased by approximately 52.1% in the presence of 200 ㎍/L C4-HSL. CLSM images showed that more bacterial cells were present on the membrane surface after the AHL application. In the COMSTAT results, biomass and thickness were increased up to 2.2 times (PAO1) and 1.6 times (multi-strains) by C4-HSL. This study clearly showed that biofilm formation was increased by the application of AHL to individual strain groups, including PAO1 and microbial consortia, and significant increases were observed when 50 or 100 ㎍/L AHL was administered. This suggests that AHL application can improve the biofilm formation of microorganisms, which could yield an enhancement in efficiency of biofilm control, such as in various biofilm reactors including membrane bioreactor and bioflocculent systems in water/wastewater treatment processes.

• Journal of Microbiology and Biotechnology
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• v.21 no.12
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• pp.1330-1335
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• 2011

N-Acyl homoserine lactones (AHLs) serve as the vital quorum-sensing signals that regulate the virulence of the pathogenic bacterium Erwinia carotovora. In the present study, an approach to efficiently restrain the pathogenicity of E. carotovora-induced soft rot disease is described. Bacillus thuringiensis-derived N-acyl homoserine lactonase (AiiA) was projected onto the surface of Pseudomonas putida cells, and inoculation with both strains was challenged. The previously identified N-terminal moiety of the ice nucleation protein, InaQ-N, was applied as the anchoring motif. A surface display cassette with inaQ-N/aiiA was constructed and expressed under the control of a constitutive promoter in P. putida AB92019. Surface localization of the fusion protein was confirmed by Western blot analysis, flow cytometry, and immunofluorescence microscopy. The antagonistic activity of P. putida MB116 expressing InaQ-N/AiiA toward E. carotovora ATCC25270 was evaluated by challenge inoculation in potato slices at different ratios. The results revealed a remarkable suppressing effect on E. carotovora infection. The active component was further analyzed using different cell fractions, and the cell surface-projected fusion protein was found to correspond to the suppressing effect.

• Biotechnology and Bioprocess Engineering:BBE
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• v.10 no.4
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• pp.322-328
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• 2005

Acylhomoserine lactones (AHLs) are known to be the triggering molecules in the quorum sensing mechanism of many gram-negative bacteria. In order to detect AHL inhibitors that are potential biofilm inhibitors, a convenient and sensitive bioassay was developed based on the $\beta$-galactosidase activity ($\beta$-GAL) of a recombinant Agrobacterium tumefaciens strain. A series of commercially available AHLs were tested for inducing $\beta$-GAL at varying concentrations in agar-plate and liquid cultures of the reporter strain. All AHLs tested exhibited a concentration­dependent induction, and octanoyl homoserine lactone (OHL) showed the highest sensitivity with a detection limit of 0.1 nM in the liquid culture assay. When fimbrolide, a known quorum sensing inhibitor, was added, induction of $\beta$-GAL by OHL was repressed. The repression at a constant OHL concentration was dependent on the fimbrolide concentration with the detection limit below 1 ppm, indicating that this assay is a sensitive method for screening AHL inhibitors.

• Microbiology and Biotechnology Letters
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• v.50 no.1
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• pp.1-14
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• 2022

Bacteria communicate with each other through an intricate communication mechanism known as quorum sensing (QS). QS regulates different behavioral aspects in bacteria, such as biofilm formation, sporulation, virulence gene expression, antibiotic production, and bioluminescence. Several different chemical signals and signal detection systems play vital roles in promoting highly efficient intra- and interspecies communication. Gram-negative bacteria coordinate gene regulation through the production of acyl homoserine lactones (AHLs). Gram-positive bacteria do not code for AHL production, while some gram-negative bacteria have an incomplete AHL-QS system. Despite this fact, these microbes can detect AHLs owing to the presence of LuxR solo receptors. Various studies have reported the role of AHLs in interspecies signaling. Moreover, as bacteria live in a polymicrobial community, the production of extracellular compounds to compete for resources is imperative. Thus, AHL-mediated signaling and inhibition are considered to affect virulence in bacteria. In the current review, we focus on the synthesis and regulation mechanisms of AHLs and highlight their role in interspecies bacterial signaling. Exploring interspecies bacterial signaling will further help us understand host-pathogen interactions, thereby contributing to the development of therapeutic strategies intended to target chronic polymicrobial infections.

• Journal of Life Science
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• v.26 no.12
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• pp.1487-1497
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• 2016

Bacterial cell to cell communication strategies called quorum sensing (QS) using small diffusible signaling molecules (auto-inducers) govern the expression of various genes dependent on their population density manner. As a consequence of synthesis and response to the signaling molecules, individual planktonic cells synchronized group behaviors to control a diverse array of phenotypes such as maturation of biofilm, production of extra-polymeric substances (EPS), virulence, bioluminescence and antibiotic production. Many studies indicated that biofilm formations are associated with QS signaling molecules such as acyl-homoserine lactones (AHLs) mainly used by several Gram negative bacteria. The biofilm maturation causes undesirable biomass accumulation in various surface environments anywhere water is present called biofouling, which results in serious eco-technological problems. Numerous molecules that interfere the bacterial QS called quorum quenching (QQ), have been discovered from various microorganisms, and their functions and mechanisms associated with QS have also been elucidated. To resolve biofouling problems related to various industries, the novel approach based on QS interference has been emerged attenuating multi-drug resisting bacteria appearance and environmental toxicities, which may provide potential advantages over the conventional anti-biofouling approaches. Therefore this paper presents recent information related to bacterial quorum sensing system, quorum quenching enzymes that can control the QS signaling, and lastly discuss the anti-biofouling approaches using the quorum quenching.

• Animal Bioscience
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• v.37 no.2_spc
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• pp.337-345
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• 2024

Ruminants possess a specialized four-compartment forestomach, consisting of the reticulum, rumen, omasum, and abomasum. The rumen, the primary fermentative chamber, harbours a dynamic ecosystem comprising bacteria, protozoa, fungi, archaea, and bacteriophages. These microorganisms engage in diverse ecological interactions within the rumen microbiome, primarily benefiting the host animal by deriving energy from plant material breakdown. These interactions encompass symbiosis, such as mutualism and commensalism, as well as parasitism, predation, and competition. These ecological interactions are dependent on many factors, including the production of diverse molecules, such as those involved in quorum sensing (QS). QS is a density-dependent signalling mechanism involving the release of autoinducer (AIs) compounds, when cell density increases AIs bind to receptors causing the altered expression of certain genes. These AIs are classified as mainly being N-acyl-homoserine lactones (AHL; commonly used by Gram-negative bacteria) or autoinducer-2 based systems (AI-2; used by Gram-positive and Gram-negative bacteria); although other less common AI systems exist. Most of our understanding of QS at a gene-level comes from pure culture in vitro studies using bacterial pathogens, with much being unknown on a commensal bacterial and ecosystem level, especially in the context of the rumen microbiome. A small number of studies have explored QS in the rumen using 'omic' technologies, revealing a prevalence of AI-2 QS systems among rumen bacteria. Nevertheless, the implications of these signalling systems on gene regulation, rumen ecology, and ruminant characteristics are largely uncharted territory. Metatranscriptome data tracking the colonization of perennial ryegrass by rumen microbes suggest that these chemicals may influence transitions in bacterial diversity during colonization. The likelihood of undiscovered chemicals within the rumen microbial arsenal is high, with the identified chemicals representing only the tip of the iceberg. A comprehensive grasp of rumen microbial chemical signalling is crucial for addressing the challenges of food security and climate targets.

• The Plant Pathology Journal
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• v.27 no.3
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• pp.242-248
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• 2011

Several soil bacteria were found to degrade N-Acylhomoserine lactones (NAHLs), thereby interfering with the bacterial quorum sensing system. In this research, fifteen strains of NAHL degrading rhizobacteria were isolated from potato rhizosphere. Based on phenotypic characteristics and 16S rDNA sequence analyses, the strains were identified as members of genera Bacillus, Streptomyces, Arthrobacter, Pseudomonas and Mesorhizobium. All tested isolates were capable to degrade both synthetic and natural NAHL produced by Pectobacterium carotovorum subsp. carotovorum (Pcc) strain EMPCC. In quorum quenching experiments selected isolates, especially Mesorhizobium sp., were markedly reduced the pathogenicity of Pcc strain EMPCC in potato tubers and totally suppressed tissue maceration on potato tubers. These led to consider the latter as a useful biocontrol agent against Pectobacterium spp.

• 한국생물공학회:학술대회논문집
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• 2002.04a
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• pp.411-414
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• 2002

Acylated homoserine lactones (AHLs) are membrane-permeant signal molecules responsible for biofilm formation of gram-negative bacteria via a unique mechanism known as quorum sensing. A target specific bioassay employing the AHL-responsive Agrobacterium tumefaciens reporter strain has been developed to identify new AHL-like compounds from natural products, which could be developed into antifouling compounds. By varying the X-gal concentration, incubation time, solvent for sample preparation and the sample loading procedure, it was possible to detect low level AHLs up to $10^1nM$. The length of the acyl chain of the AHLs was found to affect the sensitivity of this bioassay.

• Proceedings of the PSK Conference
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• 2003.04a
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• pp.224.1-224.1
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• 2003

Recent studies have revealed that bacterial biofilm production by the gram-negative bacteria is regulated by the quorum sensing signaling molecules, AHLs (N-acyl homoserine lactones). This suggests that inhibiting the AHLs could enhance the effects of antibacterial agents. Halogenated furanones purified from the red algae Delisea pulchra have been known to decrease quorum sensing responses by competitive inhibition of the AHLs. (omitted)