Quorum Sensing Is Required for the Colony Establishment of a Plant Phyllosphere Bacterium Rhodopseudomonas palustris Strain GJ-22.

The phyllosphere presents a hostile environment for many biocontrol agents; however, it is as significant as is the rhizosphere for plant health. Deploying biocontrol bacteria into the phyllosphere can efficiently suppress diseases; however, the lack of knowledge on the phyllosphere adaptive traits of biocontrol bacteria poses challenges. In this study, we demonstrated that Rhodopseudomonas palustris GJ-22 colonizes the phyllosphere by forming cell aggregates. The formation of cell aggregates required the production of exopolysaccharides (EPS), which depended on the function of the rpaI-rpaR quorum sensing (QS) mechanism, mediated by the signaling molecule p-coumaroyl-HSL (pC-HSL). The mutation of the EPS biosynthesis gene Exop1 or the signaling molecule biosynthesis gene rpaI compromised the ability of GJ-22 to tolerate reactive oxygen intermediates (ROIs), such as H2O2, in vitro and to form cell aggregates in vivo. Collectively, the results revealed that QS mediates EPS production and consequently leads to bacterial cell aggregation. IMPORTANCE Quorum sensing is used by various bacteria for coordinating the multiplication of bacterial cells in a group and for modulating the behaviors of surrounding microbial species. Host plants can benefit from this interspecies modulation, as it can disrupt the QS circuits of pathogenic bacteria. Some N-acyl homoserine lactone- (AHL-) producing bacteria that were introduced into the phyllosphere as biocontrol agents may establish AHL-based crosstalk with indigenous microbes to steer the nutritional and microecological conditions toward their own and the host plant's benefit. Here, we showed that biocontrol bacteria introduced into the phyllosphere require a functioning QS circuit to establish colonies and suppress pathogens. Furthermore, our findings provoked a broader investigation into the role of the QS circuit in beneficial microorganism-plant interactions.

Derivatized chitosan-oil-in-water nanocapsules for trans-cinnamaldehyde delivery.

trans-Cinnamaldehyde, known for its bacterial anti-quorum sensing activity when applied at sublethal concentrations, has gained traction given its potential use against multidrug resistant bacteria. In this work, trans-cinnamaldehyde-loaded oil-in-water nanocapsules coated with chitosan, N,N,N-trimethyl chitosan chloride, N-(2-(N,N,N-trimethylammoniumyl)acetyl) chitosan chloride or N-(6-(N,N,N-trimethylammoniumyl)hexanoyl)chitosan chloride were obtained. All the formulated nanocapsules showed a Z-average hydrodynamic diameter ~ 160 nm and ζ-potential higher than +40 mV. N,N,N-trimethyl chitosan-coated oil-in-water nanocapsules showed the greatest trans-cinnamaldehyde association efficiency (99.3 ± 7.6) % and total payload release (88.6 ± 22.5) %, while N-(6-(N,N,N-trimethylammoniumyl)hexanoyl)chitosan chloride chitosan-coated oil-in-water nanocapsules were the only formulations stable in phosphate buffer saline PBS (pH 7.4) upon incubation at 37 °C for 24 h. Future work should address the stability of the developed nanocapsules in culture media and their biological performance.

Promoting the healing of infected diabetic wound by an anti-bacterial and nano-enzyme-containing hydrogel with inflammation-suppressing, ROS-scavenging, oxygen and nitric oxide-generating properties.

The diabetic wound is easily to develop into a chronic wound because of the extremely serious and complex inflammatory microenvironment including biofilm formation, over-expressed reactive oxygen species (ROS), hypoxia and insufficiency of nitric oxide (NO) synthesis. In this work, a multifunctional hydrogel was designed and prepared by crosslinking hydrophilic poly(PEGMA-co-GMA-co-AAm) (PPGA) polymers with hyperbranched poly-L-lysine (HBPL)-modified manganese dioxide (MnO2) nanozymes. Pravastatin sodium, which is supposed to participate in the synthesis of NO, was further loaded to obtain the HMP hydrogel. The capabilities of this hydrogel in scavenging different types of ROS, generating O2, killing broad spectrum bacteria, and protecting cells against oxidative stress were confirmed in vitro. The transcriptome analysis revealed that HBPL inhibited bacterial quorum sensing (QS) system, downregulated virulent genes, and interfered bacterial metabolism. The HBPL-crosslinked hydrogels killed up to 94.1%-99.5% of methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli (E. coli) and Pseudomonas aeruginosa even at 109 CFU/mL. HBPL modification greatly increased the stability of MnO2 nanosheets in physiological environment. The MRSA-caused infection was effectively treated by the HBPL-crosslinked HMP hydrogel in vivo, and thereby the wound closure at inflammatory phase was promoted significantly. The treatment of HMP hydrogel reduced the ROS degree and relieved the inflammatory level significantly, accompanied by the decreased neutrophil infiltration and enhanced M2-type macrophage polarization in vivo. Significantly lower levels of inflammatory factors such as interleukin-1ß (IL-1ß), IL-6, tumor necrosis factor-α (TNF-α) and chemokines-1 (CXCL-1), and higher levels of anti-inflammatory cytokines such as IL-4 and IL-10 were also confirmed. Moreover, the HMP hydrogel could promote the secretion of transforming growth factor-ß (TGF-ß) and stimulate neovascularization, and deposition of collagen with a thicker skin and epithelium structure.

The bacterial quorum sensing molecule, 2-heptyl-3-hydroxy-4-quinolone (PQS), inhibits signal transduction mechanisms in brain tissue and is behaviorally active in mice.

Interkingdom communication between bacteria and host organisms is one of the most interesting research topics in biology. Quorum sensing molecules produced by Gram-negative bacteria, such as acylated homoserine lactones and quinolones, have been shown to interact with host cell receptors, stimulating innate immunity and bacterial clearance. To our knowledge, there is no evidence that these molecules influence CNS function. Here, we have found that low micromolar concentrations of the Pseudomonas aeruginosa quorum sensing autoinducer, 2-heptyl-3-hydroxy-4-quinolone (PQS), inhibited polyphosphoinositide hydrolysis in mouse brain slices, whereas four selected acylated homoserine lactones were inactive. PQS also inhibited forskolin-stimulated cAMP formation in brain slices. We therefore focused on PQS in our study. Biochemical effects of PQS were not mediated by the bitter taste receptors, T2R4 and T2R16. Interestingly, submicromolar concentrations of PQS could be detected in the serum and brain tissue of adult mice under normal conditions. Levels increased in five selected brain regions after single i.p. injection of PQS (10 mg/kg), peaked after 15 min, and returned back to normal between 1 and 4 h. Systemically administered PQS reduced spontaneous locomotor activity, increased the immobility time in the forced swim test, and largely attenuated motor response to the psychostimulant, methamphetamine. These findings offer the first demonstration that a quorum sensing molecule specifically produced by Pseudomonas aeruginosa is centrally active and influences cell signaling and behavior. Quorum sensing autoinducers might represent new interkingdom signaling molecules between ecological communities of commensal, symbiotic, and pathogenic microorganisms and the host CNS.

Identification and Characterization of a New Quorum-Quenching N-acyl Homoserine Lactonase in the Plant Pathogen Erwinia amylovora.

Quorum quenching (QQ) is the ability to interfere with bacterial cell to cell communication, known as quorum sensing (QS). QQ enzymes that degrade or modify acyl homoserine lactones (AHLs) have been attracting increasing interest as promising agents for inhibiting QS-mediated bacterial pathogenicity. Plant pathogens from the genus Erwinia cause diseases in several economically important crops. Fire blight is a devastating plant disease caused by Erwinia amylovora, affecting a wide range of host species within the Rosaceae and posing a major global threat for commercial apple and pear production. While QS has been described in Erwinia species, no AHL-degrading enzymes were identified and characterized. Here, phylogenetic analysis and structural modeling were applied to identify an AHL lactonase in E. amylovora (dubbed EaAiiA). Following recombinant expression and purification, the enzyme was biochemically characterized. EaAiiA lactonase activity was dependent on metal ions and effectively degraded AHLs with high catalytic efficiency. Its highest specific activity (kcat/KM value) was observed against one of the AHLs (3-oxo-C6-homoserine lactone) secreted from E. amylovora. Exogenous addition of the purified enzyme to cultures of E. amylovora reduced the formation of levan, a QS-regulated virulence factor, by 40% and the transcription level of the levansucrase-encoding gene by 55%. Furthermore, preincubation of E. amylovora cultures with EaAiiA inhibited the progress of fire blight symptoms in immature Pyrus communis fruits. These results demonstrate the ability of the identified enzyme from E. amylovora to act as a quorum-quenching lactonase.

High-Throughput Immunochemical Method to Assess the 2-Heptyl-4-quinolone Quorum Sensing Molecule as a Potential Biomarker of Pseudomonas aeruginosa Infections.

Bacterial quorum sensing (QS) is being contemplated as a promising target for developing innovative diagnostic and therapeutic strategies. Here we report for the first time the development of antibodies against 2-heptyl-4-quinolone (HHQ), a signaling molecule from the pqs QS system of Pseudomonas aeruginosa, involved in the production of important virulent factors and biofilm formation. The antibodies produced were used to develop an immunochemical diagnostic approach to assess the potential of this molecule as a biomarker of P. aeruginosa infection. The ELISA developed is able to reach a detectability in the low nM range (IC50 = 4.59 ± 0.29 nM and LOD = 0.34 ± 0.13 nM), even in complex biological samples such as Müeller Hinton (MH) culture media. The ELISA developed is robust and reproducible and has been found to be specific to HHQ, with little interference from other related alkylquinolones from the pqs QS system. The ELISA has been used to analyze the HHQ production kinetics of P. aeruginosa clinical isolates grown in MH media, pointing to its potential as a biomarker of infection and at the possibility to use the technology developed to obtain additional information about the disease stage.

Quantitative Investigation of the Role of Intra-/Intercellular Dynamics in Bacterial Quorum Sensing.

Bacteria utilize diffusible signals to regulate population density-dependent coordinated gene expression in a process called quorum sensing (QS). While the intracellular regulatory mechanisms of QS are well-understood, the effect of spatiotemporal changes in the population configuration on the sensitivity and robustness of the QS response remains largely unexplored. Using a microfluidic device, we quantitatively characterized the emergent behavior of a population of swimming E. coli bacteria engineered with the lux QS system and a GFP reporter. We show that the QS activation time follows a power law with respect to bacterial population density, but this trend is disrupted significantly by microscale variations in population configuration and genetic circuit noise. We then developed a computational model that integrates population dynamics with genetic circuit dynamics to enable accurate (less than 7% error) quantitation of the bacterial QS activation time. Through modeling and experimental analyses, we show that changes in spatial configuration of swimming bacteria can drastically alter the QS activation time, by up to 22%. The integrative model developed herein also enables examination of the performance robustness of synthetic circuits with respect to growth rate, circuit sensitivity, and the population's initial size and spatial structure. Our framework facilitates quantitative tuning of microbial systems performance through rational engineering of synthetic ribosomal binding sites. We have demonstrated this through modulation of QS activation time over an order of magnitude. Altogether, we conclude that predictive engineering of QS-based bacterial systems requires not only the precise temporal modulation of gene expression (intracellular dynamics) but also accounting for the spatiotemporal changes in population configuration (intercellular dynamics).

Synthesis and evaluation of new 3-aminooxazolidin-2-one derivatives for inhibiting bacterial quorum sensing / 国际药学研究杂志

Objective To develop some 3-aminooxazolidin-2-one derivatives with bacteria quorum sensing(QS) inhibitory activity. Methods Using (2-hydroxyethyl) hydrazine as raw material, we finished the synthesis through cyclization, condensation, hydrolysis and condensation reaction, and evaluated their inhibition of QS via Chromobacterium violaceum. Results Eight compounds were synthesized and their structures were confirmed by 1H NMR and MS characterization. Compounds Z2 had inhibitory effect against QS. Conclusion None of the eight synthesized compounds have been reported before and the synthetic route is reliable. Compounds Z2 have inhibitory effect against QS.

Synthesis and evaluation of new 3-aminooxazolidin-2-one derivatives for inhibiting bacterial quorum sensing / 国际药学研究杂志

Objective To develop some 3-aminooxazolidin-2-one derivatives with bacteria quorum sensing(QS)inhibitory ac?tivity. Methods Using(2-hydroxyethyl)hydrazine as raw material,we finished the synthesis through cyclization,condensation,hy?drolysis and condensation reaction,and evaluated their inhibition of QS via Chromobacterium violaceum. Results Eight compounds were synthesized and their structures were confirmed by 1H NMR and MS characterization. Compounds Z2 had inhibitory effect against QS. Conclusion None of the eight synthesized compounds have been reported before and the synthetic route is reliable. Compounds Z2 have inhibitory effect against QS.

QUORUM SENSING IN PLANT-ASSOCIATED BACTERIA / 微生物学通报

Bacterial N-Acyl-L-homoserine lactones (AHLs)-mediated quorum sensing is involved in the regulation of diverse biological functions. As the bacterial pathogen population density increases, AHLs concentration secreted by pathogen reaches a threshold and then interacts with their intercellular receptor and triggers expression of virulence genes. It is a promising approach to biologically control bacterial disease in plants and animals by manipulating bacterial AHL-quorum sensing with AHLs-degrading enzyme and AHL analogue.