Quorum Sensing Signaling Pathways Research Articles

Unveiling the hidden language of bacteria: anti-quorum sensing strategies for gram-negative bacteria infection control.

Quorum sensing (QS) is a communication mechanism employed by many bacteria to regulate gene expression in a population density-dependent manner. It plays a crucial role in coordinating various bacterial behaviors, including biofilm formation, virulence factor production, and antibiotic resistance. However, the dysregulation of QS can lead to detrimental effects, making it an attractive target for developing novel therapeutic strategies. Anti-QS approaches aim to interfere with QS signaling pathways, inhibiting the communication between bacteria, and disrupting their coordinated activities. Various strategies have been explored to achieve this goal. Advances in understanding QS mechanisms and the discovery of new targets have paved the way for the development of innovative anti-QS approaches. Combining multiple anti-QS strategies or utilizing them in combination with traditional antibiotics holds great promise for combating bacterial infections and addressing the challenges posed by antibiotic resistance. Anti-QS approaches offer a diverse range of strategies including natural compounds, antibody-mediated quorum quenching (QQ), computer-aided drug design for QQ, repurposing of Drugs approved by FDA as anti-QS agents and modulating quorum-sensing molecules which were discussed in detail in this review. This review, comprehensively and for the first time, sheds light on the significance of diverse anti-QS strategies in solving antimicrobial resistance problem in Gram-negative microbial infection.

Synthesis, in Silico Study and Biological Evaluation of N-(Benzothiazol/Thiazol-2-yl)benzamide Derivatives as Quorum Sensing Inhibitors against Pseudomonas aeruginosa.

The development of bacterial resistance to chemical therapy poses a severe danger to efficacy of treating bacterial infections. One of the key factors for resistance to antimicrobial medications is growth of bacteria in biofilm. Quorum sensing (QS) inhibition was created as an alternative treatment by developing novel anti-biofilm medicines. Cell-cell communication is impeded by QS inhibition, which targets QS signaling pathway. The goal of this work is to develop newer drugs that are effective against Pseudomonas aeruginosa by decreasing QS and acting as anti-biofilm agents. In this investigation, N-(benzo[d]thiazol-2-yl)benzamide/N-(thiazol-2-yl)benzamide derivatives 3a-h were designed and synthesized in good yields. Further, molecular docking analyses revealed that binding affinity values were founded -11.2 to -7.6 kcal/mol that were moderate to good. The physicochemical properties of these prepared compounds were investigated through in-silico method. Molecular dynamic simulation was also used to know better understanding of stability of the protein and ligand complex. Comparing N-(benzo[d]thiazol-2-yl)benzamide 3a to salicylic acid (4.40±0.10) that was utilised as standard for quorum sensing inhibitor, the anti-QS action was found greater for N-(benzo[d]thiazol-2-yl)benzamide 3a (4.67±0.45) than salicylic acid (4.40±0.10). Overall, research results suggested that N-(benzo[d]thiazol-2-yl)benzamide/N-(thiazol-2-yl)benzamide derivatives 3a-h may hold to develop new quorum sensing inhibitors.

Chromobacterium Violaceum: A Model for Evaluating the Anti-Quorum Sensing Activities of Plant Substances

In the new antibiotic era, the exponential increase in multiresistant bacterial strains has become the main global health problem. Many researchers have focused their efforts on exploring novel or combined strategies for combating bacterial resistance. Good knowledge of the molecular mechanisms of resistance and bacterial virulence factors as key targets provides us with a good basis for resolving the problem. One particularly attractive and promising strategy is to attack the main regulatory “network” of bacterial virulence determinants known as quorum sensing (QS). The inhibition of QS signals will be a novel means of screening more effective quorum-sensing inhibitors (QSIs) and will play a key role in the use of next-generation antimicrobials in the battle against resistance. This motivated the present review to provide a comprehensive clarification of the regulatory mechanisms of quorum-sensing signaling pathways in Chromobacterium violaceum and the discovery of potential plant quorum-sensing inhibitors.

A Streptomyces tendae Specialized Metabolite Inhibits Quorum Sensing in Group A Streptococcus.

Quorum sensing (QS) is a means of bacterial communication accomplished by microbe-produced signals and sensory systems. QS systems regulate important population-wide behaviors in bacteria, including secondary metabolite production, swarming motility, and bioluminescence. The human pathogen Streptococcus pyogenes (group A Streptococcus [GAS]) utilizes Rgg-SHP QS systems to regulate biofilm formation, protease production, and activation of cryptic competence pathways. Given their reliance on small-molecule signals, QS systems are attractive targets for small-molecule modulators that would then affect gene expression. In this study, a high-throughput luciferase assay was employed to screen an Actinobacteria-derived secondary metabolite (SM) fraction library to identify small molecule inhibitors of Rgg regulation. A metabolite produced by Streptomyces tendae D051 was found to be a general inhibitor of GAS Rgg-mediated QS. Herein, we describe the biological activity of this metabolite as a QS inhibitor. IMPORTANCE Streptococcus pyogenes, a human pathogen known for causing infections such as pharyngitis and necrotizing fasciitis, uses quorum sensing (QS) to regulate social responses in its environment. Previous studies have focused on disrupting QS as a means to control specific bacterial signaling outcomes. In this work, we identified and described the activity of a naturally derived S. pyogenes QS inhibitor. This study demonstrates that the inhibitor affects three separate but similar QS signaling pathways.

Investigating the effect of the probiotic Lactobacillus plantarum and the prebiotic fructooligosaccharides on Pseudomonas aeruginosa metabolome, virulence factors and biofilm formation as potential quorum sensing inhibitors

Pseudomonas aeruginosa (P. aeruginosa) uses quorum sensing signaling (QS) molecules to control the expression of virulence factors and biofilm formation. In this study, the effects of the probiotic's (Lactobacillus plantarum (L. plantarum)) lysate and cell-free supernatant and the prebiotic (Fructooligosaccharides (FOS)) on the levels of P. aeruginosa QS molecules, virulence factors, biofilm density and metabolites were observed. These effects were investigated using exofactor assays, crystal violet and liquid chromatography-mass spectrometry (LC-MS)-based metabolomics approach.Results showed that in comparison to untreated P. aeruginosa, the L. plantarum cell-free supernatant (5%) and FOS (2%) significantly reduced the levels of the virulence factor pyoverdine (PVD) and several metabolites in the QS pathway including Pseudomonas autoinducer-2 (PAI-2). Metabolomics study revealed that the level of different secondary metabolites involved in the biosynthesis of vitamins, amino acids and the tricarboxylic acid (TCA) cycle were also affected. L. Plantarum was found to have a higher impact on the metabolomics profile of P. aeruginosa and its QS molecules compared to FOS. Lastly, a decrease in the formation of the P. aeruginosa biofilm was observed in a time-dependent pattern upon treatment with either cell-free supernatant of L. plantarum (5%), FOS (2%) or a combination of both treatments (5% + 2%). The latter showed the highest effect with 83% reduction in biofilm density at 72 h incubation.This work highlighted the important role probiotics and prebiotics play as potential QS inhibitors for P. aeruginosa. Moreover, it demonstrated the significant role of LC-MS metabolomics for investigating the altered biochemical and QS pathways in P. aeruginosa.

Effect of quorum quenchers on virulence factors production and quorum sensing signalling pathway of non-mucoid, mucoid, and heavily mucoid Pseudomonas aeruginosa

Quorum quenching (QQ), a mechanism which inhibits, interferes or inactivates quorum sensing, has been investigated for control of biofilms instigated by quorum sensing process. Application of quorum quenchers (QQs) provides the possibility to investigate how different phenotypes of Pseudomonas aeruginosa (non-mucoid, mucoid, and heavily mucoid strains) modulate their gene expression to form biofilms, their quorum sensing (QS) mediated biofilm to be formed, and their virulence expressed. The mRNA expression of the AHL-mediated QS circuit and AHL-mediated virulence factors in P. aeruginosa was investigated in presence of QQs. qPCR analysis showed that farnesol and tyrosol actively reduce the expression of the synthase protein, LasI and RhlI, and prevent production of 3OC12-HSL and C4-HSL, respectively. Also, the use of farnesol and tyrosol significantly moderated gene expression for exo-proteins toxA, aprA, LasB, as well as rhlAB, which are responsible for rhamnolipid production. Our findings were promising, identifying several suppressive regulatory effects of furanone and Candida albicans QS signal molecules, tyrosol, and farnesol on the AHL-mediated P. aeruginosa QS network and related virulence factors.

合成生物学应用于微生物群体感应的研究进展

<p indent="0mm">Bacteria exist as a unicellular organism with their community and systematization characteristics in the environment. Quorum sensing (QS), a language for cell-cell communication, helps bacteria regulate gene expression and community behavior, leading to adaptation to environmental changes. QS system is widespread in many kingdoms of microbiomes (bacteria, fungi, and archaea), which could manipulate various physiological behaviors, including bioluminescence, biofilm formation, producing virulence factors, and establishing symbiosis. However, due to the diversity of the microbial community structure and functional complexity in nature, there are still unknown areas for QS-mediated regulatory networks and ecological mechanisms. The recent vigorous development of synthetic biology may provide new opportunities to probe and explore QS effects. This method has made great achievements in designing genetic element libraries, assembling biological devices, designing genetic circuits, and creating predefined and predictable microbiome consortia. In parallel, synthetic biology can be used as a tool in quorum sensing to regulate the composition and function of communities. Hence, an attempt was made in this review to summarize the latest research. First, we presented several typical QS systems, their functions and signaling pathways. Second, we discussed how to design QS signaling pathways and genetic circuits and how to reduce crosstalk using synthetic biology strategies. Finally, we evaluated the assay on the synthetic QS system and its performance in microbial inter- and intraspecies communication. Thus, this review aims to sort out advanced concepts of synthetic biology, deepen the understanding of constructing a bio-calculation toolkit based on the QS system, control population density and metabolic flow, and expand the application scope of synthetic biology strategy in manipulating QS.

Extracellular release of two peptidases dominates generation of the trypanosome quorum-sensing signal

Trypanosomes causing African sleeping sickness use quorum-sensing (QS) to generate transmission-competent stumpy forms in mammalian hosts. This density-dependent process is signalled by oligopeptides that stimulate the signal transduction pathway leading to stumpy formation. Here, using mass spectrometry analysis, we identify peptidases released by trypanosomes and, for 12 peptidases, confirm their extracellular delivery. Thereafter, we determine the contribution of each peptidase to QS signal production using systematic inducible overexpression in vivo, and confirm this activity operates through the physiological QS signalling pathway. Gene knockout of the QS-active peptidases identifies two enzymes, oligopeptidase B and metallocarboxypeptidase 1, that significantly reduce QS when ablated individually. Further, combinatorial gene knockout of both peptidases confirms their dominance in the generation of the QS signal, with peptidase release of oligopeptidase B mediated via an unconventional protein secretion pathway. This work identifies how the QS signal driving trypanosome virulence and transmission is generated in mammalian hosts.

Phenotypic Discovery of an Antivirulence Agent against Vibrio vulnificus via Modulation of Quorum-Sensing Regulator SmcR.

An antivirulence agent against Vibrio vulnificus named quoromycin (QM) was discovered by a phenotype-based elastase inhibitor screening. Using the fluorescence difference in two-dimensional gel electrophoresis (FITGE) approach, SmcR, a quorum-sensing master regulator and homologue of LuxR, was identified as the target protein of QM. We confirmed that the direct binding of QM to SmcR inhibits the quorum-sensing signaling pathway by controlling the DNA-binding affinity of SmcR and thus effectively alleviates the virulence of V. vulnificus in vitro and in vivo. QM can be regarded as a novel antivirulence agent for the treatment of V. vulnificus infection.

Recent Advances in Surface Nanoengineering for Biofilm Prevention and Control. Part II: Active, Combined Active and Passive, and Smart Bacteria-Responsive Antibiofilm Nanocoatings.

The second part of our review describing new achievements in the field of biofilm prevention and control, begins with a discussion of the active antibiofilm nanocoatings. We present the antibiofilm strategies based on antimicrobial agents that kill pathogens, inhibit their growth, or disrupt the molecular mechanisms of biofilm-associated increase in resistance and tolerance. These agents of various chemical structures act through a plethora of mechanisms targeting vital bacterial metabolic pathways or cellular structures like cell walls and cell membranes or interfering with the processes that underlie different stages of the biofilm life cycle. We illustrate the latter action mechanisms through inhibitors of the quorum sensing signaling pathway, inhibitors of cyclic-di-GMP signaling system, inhibitors of (p)ppGpp regulated stringent response, and disruptors of the biofilm extracellular polymeric substances matrix (EPS). Both main types of active antibiofilm surfaces, namely non-leaching or contact killing systems, which rely on the covalent immobilization of the antimicrobial agent on the surface of the coatings and drug-releasing systems in which the antimicrobial agent is physically entrapped in the bulk of the coatings, are presented, highlighting the advantages of each coating type in terms of antibacterial efficacy, biocompatibility, selective toxicity, as well as drawbacks and limitations. Developments regarding combined strategies that join in a unique platform, both passive and active elements are not omitted. In such platforms with dual functionality, passive and active strategies can be applied either simultaneously or sequentially. We especially emphasize those systems that can be reversely and repeatedly switched between the non-fouling status and the bacterial killing status, thereby allowing several bacteria-killing/surface regeneration cycles to be performed without significant loss of the initial bactericidal activity. Eventually, smart antibiofilm coatings that release their antimicrobial payload on demand, being activated by various triggers such as changes in local pH, temperature, or enzymatic triggers, are presented. Special emphasis is given to the most recent trend in the field of anti-infective surfaces, specifically smart self-defensive surfaces for which activation and switch to the bactericidal status are triggered by the pathogens themselves.

N-Benzyl Derivatives of Long-Chained 4-Amino-7-chloro-quionolines as Inhibitors of Pyocyanin Production in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a leading cause of nosocomial infections that are becoming increasingly difficult to treat due to the occurrence of antibiotic resistant strains. Since P. aeruginosa virulence is controlled through quorum sensing, small molecule treatments inhibiting quorum sensing signaling pathways provide a promising therapeutic option. Consequently, we synthesized a series of N-octaneamino-4-aminoquinoline derivatives to optimize this chemotype's antivirulence activity against P. aeruginosa via inhibition of pyocyanin production. The most potent derivative, which possesses a benzofuran substituent, provided effective inhibition of pyocyanin production (IC50 = 12 μM), biofilm formation (BFIC50 = 50 μM), and motility. Experimentally, the compound's activity is achieved through competitive inhibition of PqsR, and structure-activity data were rationalized using molecular docking studies.

Regulation of Pseudomonas aeruginosa-Mediated Neutrophil Extracellular Traps.

Pseudomonas aeruginosa is the most prevalent opportunistic pathogen in the airways of cystic fibrosis (CF) patients. The pulmonary disorder is characterized by recurrent microbial infections and an exaggerated host inflammatory immune response led primarily by influx of neutrophils. Under these conditions, chronic colonization with P. aeruginosa is associated with diminished pulmonary function and increased morbidity and mortality. P. aeruginosa has a wide array of genetic mechanisms that facilitate its persistent colonization of the airway despite extensive innate host immune responses. Loss of function mutations in the quorum sensing regulatory gene lasR have been shown to confer survival advantage and a more pathogenic character to P. aeruginosa in CF patients. However, the strategies used by LasR-deficient P. aeruginosa to modulate neutrophil-mediated bactericidal functions are unknown. We sought to understand the role of LasR in P. aeruginosa-mediated neutrophil extracellular trap (NET) formation, an important anti-microbial mechanism deployed by neutrophils, the first-line responder in the infected airway. We observe mechanistic and phenotypic differences between NETs triggered by LasR-sufficient and LasR-deficient P. aeruginosa strains. We uncover that LasR-deficient P. aeruginosa strains fail to induce robust NET formation in both human and murine neutrophils, independently of bacterial motility or LPS expression. LasR does not mediate NET release via downstream quorum sensing signaling pathways but rather via transcriptional regulation of virulence factors, including, but not restricted to, LasB elastase and LasA protease. Finally, our studies uncover the differential requirements for NADPH oxidase in NET formation triggered by different P. aeruginosa strains.

Quorum sensing: A molecular cell communication in bacterial cells

Background: Quorum sensing is a cell-to-cell communication, which is extensively observed in bacteria. This process allows the cell to detect, analyze, share and act upon various environmental stimuli based on cell density. The molecular aspect of this process is the secretion and detection of chemical signaling molecules called autoinducers (AIs), which act upon the gene expression. The quorum sensing signaling pathway is specifically observed only bulk population or in other words, the quorum sensing is effective only in high cell density. The quorum sensing circuit in the bacterial population is widely studied under the following heading; quorum sensing in Gram positive bacterium, Quorum sensing in Gram negative bacterium and the Quorum sensing with respect to Interkingdom communication. These models are studied using the widely studied models like Vibrio fischeri in Gram negative QS circuit, Staphylococcus aureus in Gram positive QS circuit and Vibrio harveyi. This review paper details the introduction of quorum sensing and their gene level explanation and how they effect on the virulence of a particular species of bacteria. This paper also throws light on the realization that the bacteria has the capable of performing coordinated activities that was so long contributed to the eukaryotic cell performance.

Design, synthesis and biological evaluation of 1,2,3-triazole based 2-aminobenzimidazoles as novel inhibitors of LasR dependent quorum sensing in Pseudomonas aeruginosa.

Bacteria regulate their phenotype, growth and population via a signalling pathway known as quorum sensing. In this process, bacteria produce signalling molecules (autoinducers) to recognize their population density. Inhibiting this quorum sensing signalling pathway is one of the potential methods to treat bacterial infection. 2-Aminobenimdazoles are reported to be the strongest inhibitors of quorum sensing against wild-type P. aeruginosa. 1,2,3-Triazole based acyl homoserine lactones are found to be good inhibitors of the quorum sensing LasR receptor. Hence, in our current study, forty 1,2,3-triazole based 2-aminobenzimdazoles were synthesized and characterized using IR, NMR, MS and elemental analysis. A single crystal was developed for N-(1H-benzo[d]imidazol-2-yl)-2-(4-nonyl-1H-1,2,3-triazol-1-yl)acetamide (6d). All final compounds were screened for in vitro quorum sensing inhibitory activity against Pseudomonas aeruginosa. The quorum sensing inhibitory activity was determined in the LasR expressing P. aeruginosa MH602 reporter strain by measuring green fluorescent protein production. Among the title compounds, N-(1H-benzo[d]imidazol-2-yl)-2-(4-(4-chlorophenyl)-1H-1,2,3-triazol-1-yl)acetamide (6i) exhibited good quorum sensing inhibitory activity of 64.99% at 250 μM. N-(1H-Benzo[d]imidazol-2-yl)-2-(4-(4-nitrophenyl)-1H-1,2,3-triazol-1-yl)acetamide (6p) exhibited the most promising quorum sensing inhibitory activity with 68.23, 67.10 and 63.67% inhibition at 250, 125 and 62.5 μM, respectively. N-(1H-Benzo[d]imidazol-2-yl)-2-(4-(4-(trifluoromethyl)phenyl)-1H-1,2,3-triazol-1-yl)acetamide (6o) and N-(5,6-dimethyl-1H-benzo[d]imidazol-2-yl)-2-(4-(4-(trifluoromethyl)phenyl)-1H-1,2,3-triazol-1-yl)acetamide (7l) also exhibited 64.25% and 65.80% quorum sensing inhibition at 250 μM. Compound 6p, the most active quorum sensing inhibitor, also displayed low cytotoxicity at the tested concentrations (25, 50 and 100 μM) against normal human embryonic kidney cell lines. Finally, a docking study using Schrodinger Glide elucidated the possible putative binding mode of the significantly active compound 6p at the active site of the target LasR receptor (PDB ID: 2UV0).

Contribution of a lectin, LecM, to the quorum sensing signalling pathway of Ralstonia solanacearum strain OE1-1.

SummaryThe soil‐borne bacterium Ralstonia solanacearum invades the roots and colonizes the intercellular spaces and then the xylem. The expression of lecM, encoding a lectin LecM, is induced by an OmpR family response regulator HrpG in R. solanacearum strain OE1‐1. LecM contributes to the attachment of strain OE1‐1 to the host cells of intercellular spaces. OE1‐1 produces methyl 3‐hydroxymyristate (3‐OH MAME) through a methyltransferase (PhcB) and extracellularly secretes the chemical as a quorum sensing (QS) signal, which activates QS. The expression of lecM is also induced by the PhcA virulence regulator functioning through QS, and the resulting LecM is implicated in the QS‐dependent production of major exopolysaccharide EPS I and the aggregation of OE1‐1 cells. To investigate the function of LecM in QS, we analysed the transcriptome of R. solanacearum strains generated by RNA sequencing technology. In the lecM mutant, the expression of positively QS‐regulated genes and negatively QS‐regulated genes was down‐regulated (by >90%) and up‐regulated (by ~60%), respectively. However, phcB and phcA in the lecM mutant were expressed at levels similar to those in strain OE1‐1. The lecM mutant produced significantly less ralfuranone and exhibited a significantly greater swimming motility, which were positively and negatively regulated by QS, respectively. In addition, the extracellular 3‐OH MAME content of the lecM mutant was significantly lower than that of OE1‐1. The application of 3‐OH MAME more strongly increased EPS I production in the phcB‐deleted mutant and strain OE1‐1 than in the lecM mutant. Thus, the QS‐dependent production of LecM contributes to the QS signalling pathway.

Non-linear hierarchy of the quorum sensing signalling pathway in bloodstream form African trypanosomes.

Trypanosoma brucei, the agents of African trypanosomiasis, undergo density-dependent differentiation in the mammalian bloodstream to prepare for transmission by tsetse flies. This involves the generation of cell-cycle arrested, quiescent, stumpy forms from proliferative slender forms. The signalling pathway responsible for the quorum sensing response has been catalogued using a genome-wide selective screen, providing a compendium of signalling protein kinases phosphatases, RNA binding proteins and hypothetical proteins. However, the ordering of these components is unknown. To piece together these components to provide a description of how stumpy formation arises we have used an extragenic suppression approach. This exploited a combinatorial gene knockout and overexpression strategy to assess whether the loss of developmental competence in null mutants of pathway components could be compensated by ectopic expression of other components. We have created null mutants for three genes in the stumpy induction factor signalling pathway (RBP7, YAK, MEKK1) and evaluated complementation by expression of RBP7, NEK17, PP1-6, or inducible gene silencing of the proposed differentiation inhibitor TbTOR4. This indicated that the signalling pathway is non-linear. Phosphoproteomic analysis focused on one pathway component, a putative MEKK, identified molecules with altered expression and phosphorylation profiles in MEKK1 null mutants, including another component in the pathway, NEK17. Our data provide a first molecular dissection of multiple components in a signal transduction cascade in trypanosomes.

Regulatory effects of Shewanella putrefaciens isolated from shrimp Penaeus orientalis on the virulence factors of Vibrio parahaemolyticus and evaluation of the role of quorum sensing in virulence factors regulation.

As an aquatic pathogen widely present in aquatic food, Vibrio parahaemolyticus causes outbreaks of gastroenteritis across the globe. Virulence factors of V. parahaemolyticus increases with the amount of spoilage in aquatic organisms including shrimp, but mechanisms regulating its virulence factors are not well understood. In this study, five spoilage bacteria isolated from shrimp were investigated for their regulatory effects on the virulence factors including haemolysin and biofilm of V. parahaemolyticus. Among these isolates, Shewanella putrefaciens induced haemolytic activity in V. parahaemolyticus in a time-dose-temperature-dependent manner and we found the main component responsible for this effect to be the supernatant or cell-free extract of S. putrefaciens. Total haemolytic activity, expression of the thermostable direct haemolysin gene tdh and biofilm production of V. parahaemolyticus were significantly up-regulated by S. putrefaciens, but also by deletion of quorum-sensing luxM or luxS gene of V. parahaemolyticus. However, this regulation by S. putrefaciens was significantly impaired by deletion of the luxM gene, but not by deletion of the luxS gene. Further study showed that S. putrefaciens exhibited a strong degradation ability on the signalling molecule acylated homoserine lactone (AHL) synthesised by the LuxM enzyme. This study revealed a novel virulence regulatory mechanism that S. putrefaciens can significantly increase the virulence factors of V. parahaemolyticus via interfering with the luxM- type quorum-sensing signalling pathway through its AHL-degradation ability.

Inhibiting PSM\u03b1-induced neutrophil necroptosis protects mice with MRSA pneumonia by blocking the agr system

Given its high resistance, enhanced virulence, and high transmissibility, community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) pneumonia is highly associated with high morbidity and mortality. Anti-virulence therapy is a promising strategy that bypasses the evolutionary pressure on the bacterium to develop resistance. RNAIII-inhibiting peptide (RIP), as an accessory gene regulator (agr)-specific inhibitor, significantly restricts the virulence of S. aureus and protects infected mice from death by blocking the agr quorum sensing system. The protective effects of RIP on the neutropenic mice completely disappeared in a neutrophil-deleted mouse infection model, but not in the macrophage-deleted mice. This result confirmed that the in vivo antibacterial activity of RIP is highly associated with neutrophil function. Phenol-soluble modulins (PSMs), as major leukocyte lysis toxins of CA-MRSA, are directly regulated by the agr system. In this experiment, PSMα1, 2, and 3 significantly induced neutrophil necroptosis by activating mixed lineage kinase-like protein (MLKL) phosphorylation and increasing lactate dehydrogenase release. The S. aureus supernatants harvested from the agr or psmα mutant strains both decreased the phosphorylation level of MLKL and cell lysis. PSMα1-mediated neutrophil lysis was significantly inhibited by necrosulfonamide, necrostatin-1, TNFα antibody, and WRW4. These results showed PSMα1 induced necroptosis depends on formylpeptide receptor 2 (FPR2)-mediated autocrine TNFα. Moreover, the neutrophil necroptosis induced by S. aureus was significantly suppressed and pneumonia was effectively prevented by the blockage of agrA and psmα expression levels. These findings indicate that PSMα-induced necroptosis is a major cause of lung pathology in S. aureus pneumonia and suggest that interfering with the agr quorum sensing signaling pathway is a potential therapeutic strategy.

Phage or foe: an insight into the impact of viral predation on microbial communities.

Since their discovery, bacteriophages have been traditionally regarded as the natural enemies of bacteria. However, recent advances in molecular biology techniques, especially data from "omics" analyses, have revealed that the interplay between bacterial viruses and their hosts is far more intricate than initially thought. On theone hand, we have become more aware of the impact of viral predation on the composition and genetic makeup of microbial communities thanks to genomic and metagenomic approaches. Moreover, data obtained from transcriptomic, proteomic, and metabolomic studies have shown that responses to phage predation are complex and diverse, varying greatly depending on the bacterial host, phage, and multiplicity of infection. Interestingly, phage exposure may alter different phenotypes, including virulence and biofilm formation. The complexity of the interactions between microbes and their viral predators is also evidenced by the link between quorum-sensing signaling pathways and bacteriophage resistance. Overall, new data increasingly suggests that both temperate and virulent phages have a positive effect on the evolution and adaptation of microbial populations. From this perspective, further research is still necessary to fully understand the interactions between phage and host under conditions that allow co-existence of both populations, reflecting more accurately the dynamics in natural microbial communities.

Glucose 6-phosphate isomerase (Pgi) is required for extracellular polysaccharide biosynthesis, DSF signals production and full virulence of Xanthomonas oryzae pv. oryzicola in rice

Xanthomonas oryzae pv. oryzicola (Xoc), the causal agent of bacterial leaf streak (BLS), recruits five carbohydrate catabolic pathways (glycolysis, ED, PPP, gluconeogenesis and TCA cycle) to acquire nutrients from host rice for parasitism and pathopoiesis. Glucose 6-phosphate isomerase (Pgi), which reversibly converts glucose 6-phosphate to fructose 6-phosphate, plays an important role in glycolysis and gluconeogenesis. In this study, we found that Pgi was essential for the pathogenicity of Xoc in rice. The mutagenesis in pgi caused the pathogen unable to effectively utilize fructose, sucrose, mannose and pyruvate for growth, but did not affect bacterial growth when glucose or galactose used as the sole carbon source. The expression of hrpX and hrpG was repressed and the transcription of hrpE, hpa3 and hrcU were enhanced when pgi or clp (encoding cAMP-regulatory protein) was mutated. Intriguingly, the mutation in pgi resulted in the transcription alteration of key genes, rpfF, rpfC, rpfG and clp, in the quorum-sensing (QS) signaling pathway mediated by diffusible signal factor (DSF) signals and significantly reduced DSF signals production compared with the wild-type. Additionally, the pgi deletion not only impaired bacterial growth and virulence in rice, but also reduced bacterial extracellular polysaccharide (EPS) biosynthesis and cell motility. The lost properties mentioned above in RΔpgi were completely restored to the wild-type levels by the presence of pgi in trans. Taken together, these findings exhibited functional roles of Pgi coordinating with the hrp system and the QS system mediated by DSF signals in carbon metabolic pathways.