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Quorum sensing is a bacterial communication process whereby bacteria produce, release, and detect extracellular signaling molecules called autoinducers to coordinate collective behaviors. In the pathogen Vibrio cholerae, the quorum-sensing autoinducer 3,5-dimethyl-pyrazin-2-ol (DPO) binds the receptor and transcription factor VqmA. The DPO-VqmA complex activates transcription of vqmR, encoding the VqmR small RNA, which represses genes required for biofilm formation and virulence factor production. Here, we show that VqmA is soluble and properly folded and activates basal-level transcription of its target vqmR in the absence of DPO. VqmA transcriptional activity is increased in response to increasing concentrations of DPO, allowing VqmA to drive the V. cholerae quorum-sensing transition at high cell densities. We solved the DPO-VqmA crystal structure to 2.0 Å resolution and compared it with existing structures to understand the conformational changes VqmA undergoes upon DNA binding. Analysis of DPO analogs showed that a hydroxyl or carbonyl group at the 2′-position is critical for binding to VqmA. The proposed DPO precursor, a linear molecule, N-alanyl-aminoacetone (Ala-AA), also bound and activated VqmA. Results from site-directed mutagenesis and competitive ligand-binding analyses revealed that DPO and Ala-AA occupy the same binding site. In summary, our structure-function analysis identifies key features required for VqmA activation and DNA binding and establishes that, whereas VqmA binds two different ligands, VqmA does not require a bound ligand for folding or basal transcriptional activity. However, bound ligand is required for maximal activity.

Quorum sensing (QS) is a chemical communication process in which bacteria produce, release, and detect extracellular signaling molecules called autoinducers. Via combined transcriptional and post-transcriptional regulatory mechanisms, QS allows bacteria to collectively alter gene expression on a population-wide scale. Recently, the TetR-family transcriptional regulator LuxT was shown to control V. harveyi qrr1, encoding the Qrr1 small RNA that functions at the core of the QS regulatory cascade. Here, we use RNA-Sequencing to reveal that, beyond control of qrr1, LuxT is a global regulator of 414 V. harveyi genes including those involved in type III secretion, siderophore production, and aerolysin toxin biosynthesis. Importantly, LuxT directly represses swrZ, encoding a GntR-family transcriptional regulator, and LuxT control of type III secretion, siderophore, and aerolysin genes occurs by two mechanisms, one that is SwrZ-dependent and one that is SwrZ-independent. All of these target genes specify QS-controlled behaviors that are enacted when V. harveyi is at low cell density. Thus, LuxT and SwrZ function in parallel with QS to drive particular low cell density behaviors. Phylogenetic analyses reveal that luxT is highly conserved among Vibrionaceae, but swrZ is less well conserved. In a test case, we find that in Aliivibrio fischeri, LuxT also represses swrZ. SwrZ is a repressor of A. fischeri siderophore production genes. Thus, LuxT repression of swrZ drives activation of A. fischeri siderophore gene expression. Our results indicate that LuxT is a major regulator among Vibrionaceae, and, in the species that also possess swrZ, LuxT functions with SwrZ to control gene expression.ImportanceBacteria precisely tune gene expression patterns to successfully react to changes that occur in the environment. Defining the mechanisms that enable bacteria to thrive in diverse and fluctuating habitats, including in host organisms, is crucial for a deep understanding of the microbial world and also for development of effective applications to promote or to combat particular bacteria. In this study, we show that a regulator called LuxT controls over 400 genes in the marine bacterium Vibrio harveyi and, moreover, that LuxT is highly conserved among Vibrionaceae species, ubiquitous marine bacteria that often cause disease. We characterize the mechanisms by which LuxT controls genes involved in virulence and nutrient acquisition. We show that LuxT functions in parallel with a set of regulators of the bacterial cell-to-cell communication process called quorum sensing to promote V. harveyi behaviors at low cell density.

Background Recent research attention has been paid to anthropogenic heat emissions (AE), temperature increase generated by human activity such as lighting, transportation, manufacturing, construction, and building climate controls. However, there is no epidemiological data available to investigate the association between anthropogenic heat emissions and metabolic syndrome (MetS), a cluster of conditions that increase risk of stroke, heart disease and diabetes. Objective To explore the relationships between AE and MetS in China. Methods We recruited 15,477 adults from the 33 Communities Chinese Health Study, a cross-sectional study in northeastern China. We retrieved anthropogenic heat flux by collecting socio-economic and energy consumption data as well as satellite-based nighttime light and Normalized Difference Vegetation Index datasets, including emissions from buildings, transportation, human metabolism, and industries. We also measured MetS components consisting of triglycerides, high density lipoprotein cholesterol, fasting glucose, systolic blood pressure, and diastolic blood pressure, and waist circumference. Restricted cubic spline models were applied to assess the associations between AE and MetS. Results The median flux of total AE was 30.98 W/m2 and industrial AE was the dominant contributor (87.64%). The adjusted odds ratio and 95% confidence interval (CI) of MetS for the 75th and 95th percentiles of the total AE against the threshold were 1.29 (95% CI: 1.21, 1.38) and 1.65 (95% CI: 1.47, 1.85). Greater AE was associated with higher odds of MetS in a dose-response pattern, and the lowest point of U-shape curve indicated the threshold effect. Participants who are young and middle-aged exhibited stronger associations between AE and MetS. Conclusions Our novel findings reveal that AE are positively associated with MetS and that associations are modified by age. Further investigations into the mechanisms of the effects are needed.

Background Chlorinated polyfluorinated ether sulfonic acids (Cl-PFESAs), a group of perfluorooctane sulfonate (PFOS) alternatives, can be widely observed in humans and environmental matrices. However, associations between exposure to Cl-PFESAs and serum lipid levels in adults are unknown. Objective To explore the relationships between Cl-PFESA levels and serum lipid levels in adults. Methods We analyzed 1238 adults from the Isomers of C8 Health Project, a cross-sectional study conducted in China from July 2015 to October 2016. The average age of the participants was 61.98 ± 14.40 years. We quantified two select legacy per- and perfluoroalkyl substances [perfluorooctanoic acid (PFOA) and PFOS] and their alternatives (6:2 and 8:2 Cl-PFESAs). We also measured four serum lipids: low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), total cholesterol (TC), and triglycerides (TG). We used generalized linear models to estimate the associations between PFASs and serum lipids, with PFASs defined as either a categorical variable divided into quartiles or as a continuous variable. Results We found that 6:2 Cl-PFESA was positively associated with serum TC and LDL-C. For instance, LDL-C levels in the highest quartile of 6:2 Cl-PFESA exposure (Q4) were significantly higher than those in the lowest quartile (Q1) [β: 0.19, 95% confidence interval (CI): 0.08, 0.30]. Further analysis showed that one ln-ng/mL increase in 6:2 Cl-PFESA exposure corresponded to a 0.10 mmol/L (95% CI: 0.05, 0.16) LDL-C increase, and that exposure to 8:2 Cl-PFESA was negatively correlated with HDL-C (β: −0.03, 95% CI: −0.05, −0.01). TC had a similar relationship with both 6:2 Cl-PFESA and legacy PFASs. Participants with a BMI ≥ 25 kg/m2 exhibited a stronger association between 6:2 Cl-PFESA and TC. Conclusions Our findings make the novel suggestion that exposure to Cl-PFESAs are adversely associated with serum lipid levels, and that such associations are also observed in legacy PFASs. Increased investigation into the effects of Cl-PFESAs exposure on human health is warranted.

Quorum sensing is a chemical communication process that bacteria use to coordinate group behaviors. Pseudomonas aeruginosa, an opportunistic pathogen, employs multiple quorum-sensing systems to control behaviors including virulence factor production and biofilm formation. One P. aeruginosa quorum-sensing receptor, called RhlR, binds the cognate autoinducer N-butryl-homoserine lactone (C4HSL), and the RhlR:C4HSL complex activates transcription of target quorum-sensing genes. Here, we use a genetic screen to identify RhlR mutants that function independently of the autoinducer. The RhlR Y64F W68F V133F triple mutant, which we call RhlR*, exhibits ligand-independent activity in vitro and in vivo. RhlR* can drive wildtype biofilm formation and infection in a nematode animal model. The ability of RhlR* to properly regulate quorum-sensing-controlled genes in vivo depends on the quorum-sensing regulator RsaL keeping RhlR* activity in check. RhlR is known to function together with PqsE to control production of the virulence factor called pyocyanin. Likewise, RhlR* requires PqsE for pyocyanin production in planktonic cultures, however, PqsE is dispensable for RhlR*-driven pyocyanin production on surfaces. Finally, wildtype RhlR protein is not sufficiently stabilized by C4HSL to allow purification. However, wildtype RhlR can be stabilized by the synthetic ligand mBTL (meta-bromo-thiolactone) and RhlR* is stable without a ligand. These features enabled purification of the RhlR:mBTL complex and of RhlR* for in vitro examination of their biochemical activities. To our knowledge, this work reports the first RhlR protein purification., Author summary The human pathogen Pseudomonas aeruginosa uses a chemical communication process called quorum sensing to orchestrate group behaviors including virulence factor production and biofilm formation. Thus, quorum sensing is essential for P. aeruginosa to be a pathogen. Quorum sensing relies on the production, release, and detection of extracellular signal molecules called autoinducers. Autoinducers are bound by partner receptor proteins, and together, autoinducer-receptor complexes control gene expression. Here, we identify, purify, and characterize a mutant version of the P. aeruginosa RhlR quorum-sensing receptor that we call RhlR*, which, remarkably, does not require its partner autoinducer to function. We show that P. aeruginosa carrying RhlR* can properly form biofilms, produce virulence factors, and infect a nematode animal used as a model for pathogenesis. Because RhlR* does not rely on an autoinducer to function, biochemical and genetic analyses that were previously not possible with RhlR could be performed with RhlR*. Indeed, our studies of RhlR* provide new insight into the workings of other P. aeruginosa quorum-sensing components, most notably, the PqsE enzyme that functions together with RhlR to control virulence factor production. We propose that RhlR* is an especially valuable tool for learning about cell-cell communication and virulence in P. aeruginosa, a pathogen of high clinical relevance.

Quorum sensing, a bacterial cell-cell communication process, controls biofilm formation and virulence factor production in Vibrio cholerae, a human pathogen that causes the disease cholera. The major V. cholerae autoinducer is (S)-3-hydroxytridecan-4-one (CAI-1). A membrane bound two-component sensor histidine kinase called CqsS detects CAI-1, and the CqsS → LuxU → LuxO phosphorelay cascade transduces the information encoded in CAI-1 into the cell. Because the CAI-1 ligand is known and because the signalling circuit is simple, consisting of only three proteins, this system is ideal for analysing ligand regulation of a sensor histidine kinase. Here we reconstitute the CqsS → LuxU → LuxO phosphorylation cascade in vitro. We find that CAI-1 inhibits the initial auto-phosphorylation of CqsS whereas subsequent phosphotransfer steps and CqsS phosphatase activity are not CAI-1-controlled. CAI-1 binding to CqsS causes a conformational change that renders His194 in CqsS inaccessible to the CqsS catalytic domain. CqsS mutants with altered ligand detection specificities are faithfully controlled by their corresponding modified ligands in vitro. Likewise, pairing of agonists and antagonists allows in vitro assessment of their opposing activities. Our data are consistent with a two-state model for ligand control of histidine kinases.

Bacterial histidine kinases transduce extracellular signals into the cytoplasm. Most stimuli are chemically undefined; therefore, despite intensive study, signal recognition mechanisms remain mysterious. We exploit the fact that quorum-sensing signals are known molecules to identify mutants in the Vibrio cholerae quorum-sensing receptor CqsS that display altered responses to natural and synthetic ligands. Using this chemical-genetics approach, we assign particular amino acids of the CqsS sensor to particular roles in recognition of the native ligand, CAI-1 ( S -3 hydroxytridecan-4-one) as well as ligand analogues. Amino acids W104 and S107 dictate receptor preference for the carbon-3 moiety. Residues F162 and C170 specify ligand head size and tail length, respectively. By combining mutations, we can build CqsS receptors responsive to ligand analogues altered at both the head and tail. We suggest that rationally designed ligands can be employed to study, and ultimately to control, histidine kinase activity.

Bacteria use a chemical communication process called quorum sensing to monitor cell density and to alter behavior in response to fluctuations in population numbers. Previous studies with Vibrio harveyi have shown that LuxR, the master quorum-sensing regulator, activates and represses >600 genes. These include six genes that encode homologs of the Escherichia coli Bet and ProU systems for synthesis and transport, respectively, of glycine betaine, an osmoprotectant used during osmotic stress. Here we show that LuxR activates expression of the glycine betaine operon betIBA-proXWV , which enhances growth recovery under osmotic stress conditions. BetI, an autorepressor of the V. harveyi betIBA-proXWV operon, activates the expression of genes encoding regulatory small RNAs that control quorum-sensing transitions. Connecting quorum-sensing and glycine betaine pathways presumably enables V. harveyi to tune its execution of collective behaviors to its tolerance to stress.

Quorum sensing (QS) is a bacterial cell-cell communication process that relies on the production and detection of extracellular signal molecules called autoinducers. QS allows bacteria to perform collective activities. Vibrio cholerae, a pathogen that causes an acute disease, uses QS to repress virulence factor production and biofilm formation. Thus, molecules that activate QS in V. cholerae have the potential to control pathogenicity in this globally important bacterium. Using a whole-cell high-throughput screen, we identified eleven molecules that activate V. cholerae QS: eight molecules are receptor agonists and three molecules are antagonists of LuxO, the central NtrC-type response regulator that controls the global V. cholerae QS cascade. The LuxO inhibitors act by an uncompetitive mechanism by binding to the pre-formed LuxO-ATP complex to inhibit ATP hydrolysis. Genetic analyses suggest that the inhibitors bind in close proximity to the Walker B motif. The inhibitors display broad-spectrum capability in activation of QS in Vibrio species that employ LuxO. To the best of our knowledge, these are the first molecules identified that inhibit the ATPase activity of a NtrC-type response regulator. Our discovery supports the idea that exploiting pro-QS molecules is a promising strategy for the development of novel anti-infectives., Author Summary The disease cholera, caused by the pathogenic bacterium Vibrio cholerae, is a major health concern in developing regions. In order to be virulent, V. cholerae must precisely control the timing of production of virulence factors. To do this, V. cholerae uses a cell-cell communication process called quorum sensing to regulate pathogenicity. In the current work, we identify and characterize new classes of small molecules that interfere with quorum-sensing-control of virulence in multiple Vibrio species. The molecules target the key quorum-sensing regulator LuxO. These molecules have the potential to be developed into new anti-infectives to combat infectious diseases of global importance.

Colicin E1 is an E. coli plasmid-encoded water-soluble protein that spontaneously inserts into lipid membranes to form a voltage-gated ion channel. We have employed a novel approach in which site-directed mutagenesis is used to provide highly specific attachment points for nitroxide spin labels. A series of colicin mutants, differing only by the position of a single cysteine residue, were prepared and selectively labeled at that cysteine. A hydrophilic sequence (398-406) within the C-terminal domain of the water-soluble form of the protein was investigated and exhibited an electron paramagnetic resonance (EPR) spectral periodicity strongly suggesting an amphiphilic alpha-helix. After removal of the N-terminus of the protein with trypsin, the spectra for this sequence indicate increased label mobility and a more flexible structure.