AiiA-mediated quorum quenching does not affect virulence or toxoflavin expression in Burkholderia glumae SL2376

Disrupting quorum sensing as a strategy to inhibit bacterial virulence in human, animal, and plant pathogens

The development of sustainable alternatives to conventional antimicrobials is needed to address bacterial virulence while avoiding selecting resistant strains in a variety of fields, including human, animal, and plant health. Quorum sensing (QS), a bacterial communication system involved in noxious bacterial phenotypes such as virulence, motility, and biofilm formation, is of utmost interest. In this study, we harnessed the potential of the lactonase SsoPox to disrupt QS of human, fish, and plant pathogens. Lactonase treatment significantly alters phenotypes including biofilm formation, motility, and infection capacity. In plant pathogens, SsoPox decreased the production of plant cell wall degrading enzymes in Pectobacterium carotovorum and reduced the maceration of onions infected by Burkholderia glumae. In human pathogens, lactonase treatment significantly reduced biofilm formation in Acinetobacter baumannii, Burkholderia cepacia, and Pseudomonas aeruginosa, with the cytotoxicity of the latter being reduced by SsoPox treatment. In fish pathogens, lactonase treatment inhibited biofilm formation and bioluminescence in Vibrio harveyi and affected QS regulation in Aeromonas salmonicida. QS inhibition can thus be used to largely impact the virulence of bacterial pathogens and would constitute a global and sustainable approach for public, crop, and livestock health in line with the expectations of the One Health initiative.

A versatile Tn7 transposon-based bioluminescence tagging tool for quantitative and spatial detection of bacteria in plants

Investigation of plant-bacteria interactions requires quantification of in planta bacterial titers by means of cumbersome and time-consuming colony-counting assays. Here, we devised a broadly applicable tool for bioluminescence-based quantitative and spatial detection of bacteria in plants. We developed vectors that enable Tn7 transposon-mediated integration of the luxCDABE luciferase operon into a specific genomic location found ubiquitously across bacterial phyla. These vectors allowed for the generation of bioluminescent transformants of various plant pathogenic bacteria from the genera Pseudomonas, Rhizobium (Agrobacterium), and Ralstonia. Direct luminescence measurements of plant tissues inoculated with bioluminescent Pseudomonas syringae pv. tomato DC3000 (Pto-lux) reported bacterial titers as accurately as conventional colony-counting assays in Arabidopsis thaliana, Solanum lycopersicum, Nicotiana benthamiana, and Marchantia polymorpha. We further showed the usefulness of our vectors in converting previously generated Pto derivatives to isogenic bioluminescent strains. Importantly, quantitative bioluminescence assays using these Pto-lux strains accurately reported the effects of plant immunity and bacterial effectors on bacterial growth, with a dynamic range of four orders of magnitude. Moreover, macroscopic bioluminescence imaging illuminated the spatial patterns of Pto-lux growth in/on inoculated plant tissues. In conclusion, our vectors offer untapped opportunities to develop bioluminescence-based assays for a variety of plant-bacteria interactions.

Prevention of biofilm formation by quorum quenching

Quorum sensing (QS) is a mechanism that enables microbial communication. It is based on the constant secretion of signaling molecules to the environment. The main role of QS is the regulation of vital processes in the cell such as virulence factor production or biofilm formation. Due to still growing bacterial resistance to antibiotics that have been overused, it is necessary to search for alternative antimicrobial therapies. One of them is quorum quenching (QQ) that disrupts microbial communication. QQ-driving molecules can decrease or even completely inhibit the production of virulence factors (including biofilm formation). There are few QQ strategies that comprise the use of the structural analogues of QS receptor autoinductors (AI). They may be found in nature or be designed and synthesized via chemical engineering. Many of the characterized QQ molecules are enzymes with the ability to degrade signaling molecules. They can also impede cellular signaling cascades. There are different techniques used for testing QS/QQ, including chromatography-mass spectroscopy, bioluminescence, chemiluminescence, fluorescence, electrochemistry, and colorimetry. They all enable qualitative and quantitative measurements of QS/QQ molecules. This article gathers the information about the mechanisms of QS and QQ, and their effect on microbial biofilm formation. Basic methods used to study QS/QQ, as well as the medical and biotechnological applications of QQ, are also described. Basis research methods are also described as well as medical and biotechnological application.

Exploiting quorum sensing to confuse bacterial pathogens

Cell-cell communication, or quorum sensing, is a widespread phenomenon in bacteria that is used to coordinate gene expression among local populations. Its use by bacterial pathogens to regulate genes that promote invasion, defense, and spread has been particularly well documented. With the ongoing emergence of antibiotic-resistant pathogens, there is a current need for development of alternative therapeutic strategies. An antivirulence approach by which quorum sensing is impeded has caught on as a viable means to manipulate bacterial processes, especially pathogenic traits that are harmful to human and animal health and agricultural productivity. The identification and development of chemical compounds and enzymes that facilitate quorum-sensing inhibition (QSI) by targeting signaling molecules, signal biogenesis, or signal detection are reviewed here. Overall, the evidence suggests that QSI therapy may be efficacious against some, but not necessarily all, bacterial pathogens, and several failures and ongoing concerns that may steer future studies in productive directions are discussed. Nevertheless, various QSI successes have rightfully perpetuated excitement surrounding new potential therapies, and this review highlights promising QSI leads in disrupting pathogenesis in both plants and animals.

Quorum quenching enzymes and their application in degrading signal molecules to block quorum sensing-dependent infection

With the emergence of antibiotic-resistant strains of bacteria, the available options for treating bacterial infections have become very limited, and the search for a novel general antibacterial therapy has received much greater attention. Quorum quenching can be used to control disease in a quorum sensing system by triggering the pathogenic phenotype. The interference with the quorum sensing system by the quorum quenching enzyme is a potential strategy for replacing traditional antibiotics because the quorum quenching strategy does not aim to kill the pathogen or limit cell growth but to shut down the expression of the pathogenic gene. Quorum quenching enzymes have been identified in quorum sensing and non-quorum sensing microbes, including lactonase, acylase, oxidoreductase and paraoxonase. Lactonase is widely conserved in a range of bacterial species and has variable substrate spectra. The existence of quorum quenching enzymes in the quorum sensing microbes can attenuate their quorum sensing, leading to blocking unnecessary gene expression and pathogenic phenotypes. In this review, we discuss the physiological function of quorum quenching enzymes in bacterial infection and elucidate the enzymatic protection in quorum sensing systems for host diseases and their application in resistance against microbial diseases.