In vitro investigation of relationship between quorum-sensing system genes, biofilm forming ability, and drug resistance in clinical isolates of Pseudomonas aeruginosa.

BACKGROUND: Pseudomonas aeruginosa is an opportunistic pathogen in the health-care systems and one of the primary causative agents with high mortality in hospitalized patients, particularly immunocompromised. The limitation of effective antibiotic administration in multidrug-resistant and extensively drug-resistant P. aeruginosa isolates leads to the development of nosocomial infections and health problems. Quorum sensing system contributes to biofilm formation, expression of bacterial virulence factors, and development of drug resistance, causing prolonged patient infections. Therefore, due to the significance of the quorum sensing system in increasing the pathogenicity of P. aeruginosa, the primary objective of our study was to investigate the frequency of quorum sensing genes, as well as the biofilm formation and antibiotic resistance pattern among P. aeruginosa strains. METHODS: A total of 120 P. aeruginosa isolates were collected from different clinical specimens. The disk diffusion method was applied to detect the antibiotic resistance pattern of P. aeruginosa strains. Also, the microtiter plate method was carried out to evaluate the biofilm-forming ability of isolates. Finally, the frequency of rhlI, rhlR, lasI, and lasR genes was examined by the polymerase chain reaction method. RESULTS: In total, 88.3% P. aeruginosa isolates were found to be multidrug-resistant, of which 30.1% had extensively drug-resistant pattern. The highest and lowest resistance rates were found against ceftazidime (75.0%) and ciprofloxacin (46.6%), respectively. Also, 95.8% of isolates were able to produce biofilm, of which 42.5%, 33.3%, and 20.0% had strong, moderate, and weak biofilm patterns, respectively. The frequency of quorum sensing genes among all examined strains was as follows: rhlI (81.6%), rhlR (90.8%), lasI (89.1%), and lasR (78.3%). The most common type of quorum sensing genes among multidrug-resistant isolates were related to rhlR and lasI genes with 94.3%. Furthermore, rhlI, rhlR, and lasI genes were positive for all extensively drug-resistant isolates. However, the lasR gene had the lowest frequency among both multidrug-resistant (83.0%) and extensively drug-resistant (90.6%) isolates. Moreover, rhlR (94.7%) and lasR (81.7%) genes had the highest and lowest prevalence among biofilm-forming isolates, respectively. CONCLUSION: Our findings disclosed the significantly high prevalence of drug resistance among P. aeruginosa isolates. Also, the quorum sensing system had a significant correlation with biofilm formation and drug resistance, indicating the essential role of this system in the emergence of nosocomial infections caused by P. aeruginosa.

Study on molecular epidemiology of carbapenem resistant Pseudomonas aeruginosa and related genes of quorum sensing signal system.

This study aims to investigate the drug resistance, regulation mechanism of quorum sensing system, expression of related virulence genes, and epidemiological characteristics of carbapenem-resistant Pseudomonas aeruginosa (CRPA).In this study, Polymerase chain reaction amplification was performed to evaluate carbapenemase genes, OprD2 gene, quorum sensing system, and related virulence genes. Bacterial genotypes were analyzed using multilocus sequence typing and evolutionary analysis was conducted based on the goeBURST algorithm. The results demonstrated that a total of 47 CRPA strains were collected in this study, primarily from respiratory specimens in the ICU. Drug sensitivity results showed that the resistance rates of the 47 CRPA strains were highest for imipenem (97.87 %). The loss of OprD2 may be the main factor contributing to carbapenem resistance in our hospital's CRPA strains.All isolates tested positive for the quorum sensing system genes lasI and rhlI/R, and the virulence gene lasB was detected in all isolates, while the algD gene was detected in 19.15 % of the isolates. Among the 47 strains, 6 were untypeable, and the 41 strains with 28 different sequence types were clustered into three clonal complexes (BG1, BG2, and BG3).In conclusion, the CRPA isolates from our hospital exhibit high genetic diversity, with the deletion of the OprD2 gene possibly being the primary determinant of carbapenem resistance in Pseudomonas aeruginosa.Moreover, Las and RhI systems play a key role in quorum sensing signal system. Further research and development of drugs targeting quorum sensing signaling system may provide valuable guidance for the treatment of CRPA.

[Research progress of traditional Chinese medicines as quorum sensing inhibitors in collaboration with antibiotics to inhibit drug-resistant bacteria].

Quorum sensing system regulates the expression of genes related to bacterial growth, metabolism and other behaviors by sensing bacterial density, and controls the unified action of the entire bacterial population. This mechanism can ensure the normal secretion of bacterial metabolites and the stability of the biofilm microenvironment, providing protection for the formation of biofilms and the normal growth and reproduction of bacteria. Traditional Chinese medicine, capable of quorum sensing inhibition, can inhibit the formation of bacterial biofilms, reduce bacterial resistance, and enhance the anti-infection ability of antibiotics when combined with antibiotics. In recent years, the combination of traditional Chinese and Western medicine in the treatment of drug-resistant bacterial infections has become a research hotspot. Starting with the associations between quorum sensing, biofilm and drug-resistant bacteria, this paper reviews the relevant studies about the combined application of traditional Chinese medicines as quorum sensing inhibitors with antibiotics in the treatment of drug-resistant bacteria. This review is expected to provide ideas for the development of new clinical treatment methods and novel anti-infection drugs.

The Construction of the Self-Induced Sal System and Its Application in Salicylic Acid Production.

The design and construction of more complex and delicate genetic control circuits suffer from poor orthogonality in quorum sensing (QS) systems. The Sal system, which relies on salicylic acid as a signaling molecule, is an artificially engineered regulatory system with a structure that differs significantly from that of natural QS signaling molecules. Salicylic acid is an important drug precursor, mainly used in the production of drugs such as aspirin and anti-HIV drugs. However, there have been no reports on the construction of a self-induced Sal system in single cells. In this study, a high-copy plasmid backbone was used to construct the regulatory proteins and a self-induced promoter of salicylic acid in E. coli by adjusting the precise regulation of key gene expression; the sensitivity and induction range of this system were improved. Subsequently, the exogenous gene pchBA was introduced in E. coli to extend the shikimate pathway and synthesize salicylic acid, resulting in the construction of the first complete self-induced Sal system. Finally, the self-induced Sal System was combined with artificial trans-encoded sRNAs (atsRNAs) to repress the growth-essential gene ppc and accumulate the precursor substance PEP, thereby increasing the titer of salicylic acid by 151%. This construction of a self-induced artificial system introduces a new tool for selecting communication tools and induction systems in synthetic biology and metabolic engineering, but also demonstrates a self-inducible pathway design strategy for salicylic acid biosynthesis.

Role of the fsr Quorum-Sensing System in Enterococcus faecalis Bloodstream Infection.

Enterococcus faecalis is an important intestinal colonizing bacteria and can cause various tissue infections, including invasive blood infection (BI). The annual incidence of E. faecalis BI has been estimated to be ~4.5 per 100,000, with a fatality rate that can reach 20%. However, whether bacterial colonization or invasive infections are tissue based has not been thoroughly studied. In this study, we analyzed 537 clinical isolates from 7 different tissues to identify the key genomic elements that facilitate the colonization and invasive infection of E. faecalis. Comparative genomic analysis revealed that the BI E. faecalis isolates had the largest genome size but the lowest GC content, fsr quorum-sensing system genes were enriched in the BI E. faecalis, and the fsr gene cluster could enhance biofilm formation and serum resistance ability. Our findings also provide deep insight into the genomic differences between different tissue isolates, and the fsr quorum-sensing systems could be a key factor promoting E. faecalis invasion into the blood. IMPORTANCE First, we conducted an advanced study on the genomic differences between colonizing and infecting E. faecalis, which provides support and evidence for early and accurate diagnoses. Second, we discovered that fsr was significantly associated with blood infections, which also provides additional information for studies exploring the invasiveness of E. faecalis. Most importantly, we found that fsr played an important role in both biofilm formation and serum resistance ability in E. faecalis.

Luteolin attenuates the pathogenesis of Staphylococcus aureus by interfering with the agr system.

Staphylococcus aureus is a serious human pathogen that causes a wide variety of infectious diseases with high morbidity and mortality. Luteolin was recently shown to inhibit biofilm formation and reduce the production of virulence factors and the transcription of agrA in S. aureus. Given the broad impacts of the agr quorum-sensing system on the biofilm formation and virulence factors of S. aureus, this study aimed to investigate the effects of luteolin on the agr system and pathogenicity of S. aureus. Here, we show that at subminimal inhibitory concentrations (sub-MICs) that have no effect on bacterial growth, luteolin can markedly inhibit the adhesion and biofilm formation of both wild-type (WT) and agr mutant strains of S. aureus strain Newman. The hemolytic activity and toxin protein levels were markedly decreased in the culture supernatants of luteolin-treated WT strain but not the luteolin-treated agr mutant strain. qRT-PCR analysis showed that upon luteolin treatment, the expression of genes involved in virulence and biofilm formation was downregulated in the WT S. aureus strain, and the inefficacy of luteolin with respect to the virulence factors of only the agr mutant confirmed the agr-mediated antivirulence potential of luteolin. Furthermore, treatment with sub-MIC luteolin attenuated human alveolar epithelial A549 cell injury caused by the WT Newman strain and protected mice from pneumonia caused by the WT strain, but these effects were not observed with the agr mutant strain. These findings indicate that luteolin is a promising compound that interferes with the agr system and can be developed into novel therapeutic drugs against S. aureus infections.

Fighting multidrug-resistant Enterococcus faecalis via interfering with virulence factors using green synthesized nanoparticles.

This study aims to synthesize silver nanoparticles by the green method and test it against specific virulence factors in multi-drug resistant Enterococcus faecalis bacteria. virulence factors of E. faecalis clinical isolates were determined and the most potent isolate was selected for further investigations. The prepared Ag-NPs were characterized using UV spectroscopy, FTIR spectroscopy, dynamic light scattering, and transmission electron microscopy (TEM). The result revealed the concentration of 0.0625 mg/ml Ag-NPs was significantly reducing virulence factors in multidrug-resistant E. faecalis without affecting planktonic cell growth. UV-Visible spectroscopy characterization revealed a characteristic surface Plasmon band [SPR] at a wavelength ranging from 256 to 345 and 510 nm in the prepared Ag-NPs. dynamic light scattering indicated it tended to an electrostatic attraction between nanoparticles in the prepared solution. TEM images revealed the average size of Ag-NPs were prepared to be 28.8 nm and the shape was spherical. Green synthesized Ag-NPs have the ability to combat multi-drug-resistant E. faecalis via reducing virulence factors, which is considered a good approach toward resolving the multidrug resistance crisis.

Serum resistance factors in avian pathogenic Escherichia coli mediated by ETT2 gene cluster.

Serum resistance is a poorly understood but common trait of some systemic disease pathogenic strains of bacteria. In this study, we analysed the role Escherichia coli type III secretion system 2 (ETT2) of avian pathogenic Escherichia coli (APEC) in serum resistance by bacteria survival number in serum culture, mRNA Seq and Tandem Mass Tag™ (TMT™) detection, lipopolysaccharide (LPS) extraction, and biofilm formation detection. We found that the ETT2 gene cluster deletion strain (ΔETT2) is more resistant to the killing effect of serum than wild-type APEC40. The analysis of ΔETT2 compared to APEC40 in the transcriptomics and proteomics data showed that ETT2 has a negative effect in the ATP-binding cassette (ABC) translator system and quorum sensing system and a positive effect in purine metabolism. ETT2 may affect the LPS, biofilm, flagella, and fimbriae which may affect the serum resistance. These results could lead to effective strategies for managing the infection by APEC. The mRNA Seq data of this study are available in the Sequence Read Archive of the National Center for Biotechnology Information under the BioProject PRJNA757182, and proteomic raw data have been deposited under the accession number IPX0003420000 at iProX.

Effect of chlorogenic acid on the quorum-sensing system of clinically isolated multidrug-resistant Pseudomonas aeruginosa.

AIMS: Quorum sensing (QS) is the intercellular communication used by bacteria to regulate collective behaviour. QS regulates the production of virulence factors in many bacterial species and is considered to be an attractive target for reducing bacterial pathogenicity. Chlorogenic acid (CA) is abundant in vegetables, fruits, and traditional Chinese medicine, and has multiple activities. This study aimed to investigate the QS quenching activity of CA against clinically isolated multidrug-resistant Pseudomonas aeruginosa. METHODS AND RESULTS: The results showed that CA inhibited the mobility of bacteria, reduced the production of pyocyanin, and inhibited the activity of elastase. Furthermore, crystal violet staining and scanning electron microscope experiments showed that CA inhibited the formation of multidrug-resistant P. aeruginosa biofilm. CA at or below the concentration of 2560 µg/mL exerted negligible cytotoxicity to RAW264.7 cells. The study also examined the expression of QS-related genes, including lasI, lasR, rhlI, rhlR, pqsA, and pqsR in P. aeruginosa and found that the expression of these genes was down-regulated under CA treatment. CONCLUSIONS: The study showed that CA could be used as an anti-virulence factor for treating clinical P. aeruginosa infection. SIGNIFICANCE AND IMPACT OF STUDY: For the first time, this study took clinically isolated multidrug-resistant P. aeruginosa as the experimental object, and suggested that CA might be an effective antimicrobial compound targeting QS in treating P. aeruginosa infection, thus providing a new therapeutic direction for treating bacterial infection and effectively alleviating bacterial resistance.

Complementary Regulation of BfmRS Two-Component and AbaIR Quorum Sensing Systems to Express Virulence-Associated Genes in Acinetobacter baumannii.

Acinetobacter baumannii expresses various virulence factors to adapt to hostile environments and infect susceptible hosts. This study investigated the regulatory network of the BfmRS two-component and AbaIR quorum sensing (QS) systems in the expression of virulence-associated genes in A. baumannii ATCC 17978. The ΔbfmS mutant exhibited a significant decrease in surface motility, which presumably resulted from the low expression of pilT and A1S_0112-A1S_0119 gene cluster. The ΔbfmR mutant displayed a significant reduction in biofilm and pellicle formation due to the low expression of csu operon. The deletion of abaR did not affect the expression of bfmR or bfmS. However, the expression of abaR and abaI was upregulated in the ΔbfmR mutant. The ΔbfmR mutant also produced more autoinducers than did the wild-type strain, suggesting that BfmR negatively regulates the AbaIR QS system. The ΔbfmS mutant exhibited no autoinducer production in the bioassay system. The expression of the A1S_0112-A1S_0119 gene cluster was downregulated in the ΔabaR mutant, whereas the expression of csu operon was upregulated in this mutant with a high cell density. In conclusion, for the first time, we demonstrated that the BfmRS-AbaIR QS system axis regulated the expression of virulence-associated genes in A. baumannii. This study provides new insights into the complex network system involved in the regulation of virulence-associated genes underlying the pathogenicity of A. baumannii.

Application of quorum sensing system in microbial synthesis of valuable chemicals: a mini-review.

With advantages of low substrates cost, high optical purity of end products and environmentally friendly fermentation process, microbial production of valuable chemicals grow rapidly. Compared with static microbial strain engineering strategies, such as gene deletion, overexpression and mutation, dynamic pathway regulation is a new approach that balances cellular growth and chemical production. Quorum sensing is a natural microbial communication system responsible for cell-density-related cell behaviors. Accordingly, quorum sensing systems can be employed to achieve dynamic regulation in microorganisms without the need for manual intervention or the use of chemical inducers. In this review, natural quorum sensing systems are firstly summarized. Then, recent progress in using quorum sensing circuits in the field of metabolic engineering is highlighted. The current application challenges of quorum sensing systems and future perspectives in microbial synthesis of chemicals are also discussed.

Coordinated regulation of anthranilate metabolism and bacterial virulence by the GntR family regulator MpaR in Pseudomonas aeruginosa.

The GntR family regulators are widely distributed in bacteria and play critical roles in metabolic processes and bacterial pathogenicity. In this study, we describe a GntR family protein encoded by PA4132 that we named MpaR (MvfR-mediated PQS and anthranilate regulator) for its regulation of Pseudomonas quinolone signal (PQS) production and anthranilate metabolism in Pseudomonas aeruginosa. The deletion of mpaR increased biofilm formation and reduced pyocyanin production. RNA sequencing analysis revealed that the mRNA levels of antABC encoding enzymes for the synthesis of catechol from anthranilate, a precursor of the PQS, were most affected by mpaR deletion. Data showed that MpaR directly activates the expression of mvfR, a master regulator of pqs system, and subsequently promotes PQS production. Accordingly, deletion of mpaR activates the expression of antABC genes, and thus, increases catechol production. We also demonstrated that MpaR represses the rhl quorum-sensing (QS) system, which has been shown to control antABC activity. These results suggested that MpaR function is integrated into the QS regulatory network. Moreover, mutation of mpaR promotes bacterial survival in a mouse model of acute pneumonia infection. Collectively, this study identified a novel regulator of pqs system, which coordinately controls anthranilate metabolism and bacterial virulence in P. aeruginosa.

The production of bacterial cellulose in Gluconacetobacter xylinus regulated by luxR overexpression of quorum sensing system.

Quorum sensing is a mechanism that facilitates cell-to-cell communication. Through signal molecular density for signal recognition, which leads to the regulation of some physiological and biochemical functions. Gluconacetobacter xylinus CGMCC 2955, which produces bacterial cellulose (BC), synthesizes the LuxR protein belonging to the LuxI/LuxR type QS system. Here, a luxR overexpression vector was transformed into G. xylinus CGMCC 2955. The overexpression of luxR increased the yield of BC by 15.6% after 16 days static culture and reduced the cell density by 15.5% after 120-h-agitated culture. The glucose was used up by G. xylinus-pMV24-luxR at 72-h-agitated fermentation, which 12 h earlier than the wild-type (WT). The total N-acylhomoserine lactones (AHL) content of the luxR-overexpressing strain and the WT strain attained 1367.9 ± 57.86 mg/L and 842.9 ± 54.22 mg/L, respectively. The C12-HSL and C14-HSL contents of G. xylinus-pMV24-luxR were 202 ± 21.66 mg/L and 409.6 ± 0.91 mg/L, which were significantly lower than that of WT. In contrast, C6-HSL showed opposite results. The difference of AHL content proved that overexpression of luxR improved the binding of AHL and showed preference for some specific AHL. The metabolic results demonstrated that upon glucose exhaustion, the consumption of gluconic acid was promoted by luxR overexpression, and the content of D- ( +)-trehalose, an antiretrograde metabolite, increased significantly. KEY POINTS: • The overexpression of luxR increased the yield of bacterial cellulose • The content of signal molecules was significantly different • Differential metabolites were involved in multiple metabolic pathways.

rpeA, a global regulator involved in mupirocin biosynthesis in Pseudomonas fluorescens NCIMB 10586.

Mupirocin, a polyketide antibiotic produced by Pseudomonas fluorescens, is used as a topical antimicrobial treatment to cure various skin infections. Quorum sensing system plays an important role in regulation of mupirocin biosynthesis in P. fluorescens NCIMB 10586. In Pseudomonas, the RpeA/RpeB two-component signal transduction (TCST) system regulates quorum sensing system. However, the influences of the RpeA/RpeB TCST system on mupirocin production or other cell activities have not been studied. In this work, the homologous genes of rpeA and rpeB in P. fluorescens NCIMB 10586 were identified and inactivated in the chromosome, respectively. The deletion of rpeA reduced the mupirocin production from 160 in the wild-type to 21.3 mg/L along with slightly decreased cell growth, while no significant effected on mupirocin production in the rpeB mutant. Next, it was found that the RpeA/RpeB TCST system regulated the biosynthesis of mupirocin by modulating the quorum sensing system. Furthermore, untargeted metabolomics analysis was employed to detect the influences of RpeA on other cell activities modulated by quorum sensing system. Combined with quantitative real-time PCR, the results demonstrated that RpeA also regulated other cell activities including central carbon, amino acids, fatty acids, and purine metabolism. Overall, this study expands the current understanding of the RpeA/RpeB TCST system and provides several targets for increasing yields of mupirocin. KEY POINTS: • In P. fluorescens, the RpeA/RpeB TCST system regulates the biosynthesis of mupirocin. • RpeA modulates the cell activities through effecting the central carbon metabolism.

Quercetin inhibits Pseudomonas aeruginosa biofilm formation via the vfr-mediated lasIR system.

Pseudomonas aeruginosa is one of the most common opportunistic pathogens that cause biofilm-associated infections. Biofilm formation is partially regulated by the quorum sensing (QS) system, and quercetin can inhibit QS, biofilm formation and virulence factors. We therefore speculated that quercetin would inhibit the formation of P. aeruginosa biofilm via the QS system. In this study, we successfully constructed lasI, rhlI and lasI/rhlI gene-knockout strains. The knockout of the lasI and lasI/rhlI genes resulted in decreases in adhesion, biofilm formation, swarming motility and the expression of biofilm-associated genes, whereas deletion of the rhlI gene had no obvious influence on these biofilm-related indicators with the exception of the swarming motility. After treatment with quercetin, the lasI- and lasI/rhlI-mutant strains exhibited increased adhesion, biofilm formation, swarming motility and biofilm-associated gene expression compared with the control group. However, quercetin still exerted an inhibitory effect on these physiological factors and the biofilm-associated gene expression in the rhlI-mutant strain. The knockout of QS genes reduced the production of pyocyanin and protease activity, but after the virulence factors of the QS-mutant strains treated with quercetin showed almost no differences compared with those of the control group. In addition, quercetin could significantly inhibit vfr gene expression regardless of the presence of QS genes. The results indicated that quercetin might inhibit the lasIR system through the vfr gene and ultimately the formation of P. aeruginosa biofilms.

A novel Rap-Phr system in Bacillus velezensis NAU-B3 regulates surfactin production and sporulation via interaction with ComA.

Several quorum sensing systems occurring in Bacillus subtilis, e.g. Rap-Phr systems, were reported to interact with major regulatory proteins, such as ComA, DegU, and Spo0A, in order to regulate competence, sporulation, and synthesis of secondary metabolites. In this study, we characterized a novel Rap-Phr system, RapA4-PhrA4, in Bacillus velezensis NAU-B3. We found that the rapA4 and phrA4 genes were co-transcribed in NAU-B3. When rapA4 was expressed in the heterologous host Bacillus subtilis OKB105, surfactin production and sporulation were severely inhibited. However, when the phrA4 was co-expressed, the RapA4 activity was inhibited. The transcription of the surfactin synthetase srfA gene and sporulation-related genes were also regulated by the RapA4-PhrA4 system. In vitro results obtained from electrophoretic mobility shift assay (EMSA) proved that RapA4 inhibits ComA binding to the promoter of the srfA operon, and the PhrA4 pentapeptide acts as anti-activator of RapA4. We also found that the F24 residue plays a key role in RapA4 function. This study indicated that the novel RapA4-PhrA4 system regulates the surfactin synthesis and sporulation via interaction with ComA, thereby supporting the bacterium to compete and to survive in a hostile environment. KEY POINTS: •Bacillus velezensis NAU-B3 has a novel Rap-Phr quorum sensing system, which does not occur in model strains Bacillus subtilis 168 and B. velezensis FZB42. •RapA4-PhrA4 regulates surfactin production and sporulation. •RapA4-PhrA4 interacts with the ComA protein from ComP/ComA two-component system.

Allicin inhibits Pseudomonas aeruginosa virulence by suppressing the rhl and pqs quorum-sensing systems.

Pseudomonas aeruginosa is a virulent bacterium that secretes a variety of virulence factors that aid in establishing infections in individuals. Allicin, derived from garlic, has been shown to inhibit virulence factor production and biofilm formation in P. aeruginosa. However, the mechanisms underlying the allicin-mediated regulation of P. aeruginosa virulence remain unclear. In this study, we investigated the possible mechanisms underlying allicin-mediated virulence regulation in P. aeruginosa. The results showed that allicin attenuates the production of P. aeruginosa virulence-associated factors, such as elastase, pyocyanin, pyoverdine, and rhamnolipids, by inhibiting the rhl and pqs quorum-sensing systems. Further analysis revealed that the rhl and pqs systems play different roles during the allicin-mediated regulation process. Taken together, these results support the potential use of allicin as a therapeutic agent in controlling P. aeruginosa infection and associated mechanisms.

Identification of Quorum-Sensing Molecules of N-Acyl-Homoserine Lactone in Gluconacetobacter Strains by Liquid Chromatography-Tandem Mass Spectrometry.

Many Gram-negative bacteria can regulate gene expression in a cell density-dependent manner via quorum-sensing systems using N-acyl-homoserine lactones (AHLs), which are typical quorum-sensing signaling molecules, and thus modulate physiological characteristics. N-acyl-homoserine lactones are small chemical molecules produced at low concentrations by bacteria and are, therefore, difficult to detect. Here, a biosensor system method and liquid chromatography-tandem mass spectrometry were combined to detect and assay AHL production. As demonstrated by liquid chromatography-tandem mass spectrometry, Gluconacetobacter xylinus CGMCC No. 2955, a Gram-negative acetic acid-producing bacterium and a typical bacterial cellulose (BC) biosynthesis strain, produces six different AHLs, including N-acetyl-homoserine lactone, N-butanoyl-homoserine lactone, N-hexanoyl-homoserine lactone, N-3-oxo-decanoyl-homoserine lactone, N-dodecanoyl-homoserine lactone, and N-tetradecanoyl-homoserine lactone. Gluconacetobacter sp. strain SX-1, another Gram-negative acetic acid-producing bacterium, which can synthesize BC, produces seven different AHLs including N-acetyl-homoserine lactone, N-butanoyl-homoserine lactone, N-hexanoyl-homoserine lactone, N-3-oxo-octanoyl-homoserine lactone, N-decanoyl-homoserine lactone, N-dodecanoyl-homoserine lactone, and N-tetradecanoyl-homoserine lactone. These results lay the foundation for investigating the relationship between BC biosynthesis and quorum-sensing systems.

RpoN-Dependent Direct Regulation of Quorum Sensing and the Type VI Secretion System in Pseudomonas aeruginosa PAO1.

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen of humans, particularly those with cystic fibrosis. As a global regulator, RpoN controls a group of virulence-related factors and quorum-sensing (QS) genes in P. aeruginosa To gain further insights into the direct targets of RpoN in vivo, the present study focused on identifying the direct targets of RpoN regulation in QS and the type VI secretion system (T6SS). We performed chromatin immunoprecipitation coupled with high-throughput sequencing (ChIP-seq) that identified 1,068 binding sites of RpoN, mostly including metabolic genes, a group of genes in QS (lasI, rhlI, and pqsR) and the T6SS (hcpA and hcpB). The direct targets of RpoN have been verified by electrophoretic mobility shifts assays (EMSA), lux reporter assay, reverse transcription-quantitative PCR, and phenotypic detection. The ΔrpoN::Tc mutant resulted in the reduced production of pyocyanin, motility, and proteolytic activity. However, the production of rhamnolipids and biofilm formation were higher in the ΔrpoN::Tc mutant than in the wild type. In summary, the results indicated that RpoN had direct and profound effects on QS and the T6SS.IMPORTANCE As a global regulator, RpoN controls a wide range of biological pathways, including virulence in P. aeruginosa PAO1. This work shows that RpoN plays critical and global roles in the regulation of bacterial pathogenicity and fitness. ChIP-seq provided a useful database to characterize additional functions and targets of RpoN in the future. The functional characterization of RpoN-mediated regulation will improve the current understanding of the regulatory network of quorum sensing and virulence in P. aeruginosa and other bacteria.

The LuxS/AI-2 system of Streptococcus suis.

Quorum sensing (QS) is an important protective mechanism that allows bacteria to adapt to its environment. A limited number of signal molecules play the key role of transmitting information in this mechanism. Signals are transmitted between individual bacterium through QS systems, resulting in the expression of specific genes. QS plays an important role in a variety of bacterial processes, including drug resistance, biofilm formation, motility, adherence, and virulence. Most Gram-positive and Gram-negative bacteria possess QS systems, mainly the LuxS/AI-2-mediated QS system. Evidence has been brought that LuxS/AI-2 system controls major virulence determinants in Streptococcus suis and, as such, the ability of this bacterial species to cause infections in humans and pigs. Understanding the S. suis LuxS/AI-2 system may open up novel avenues for decreasing the drug resistance and infectivity of S. suis. This article focuses on the progress made to date on the S. suis LuxS/AI-2-mediated QS system.