Phenazine virulence factor binding to extracellular DNA is important for Pseudomonas aeruginosa biofilm formation

Unveiling the role of PA0730.1 sRNA in Pseudomonas aeruginosa virulence and biofilm formation: Exploring rpoS and mucA regulation

Small RNA (sRNA) in bacteria serve as the key messengers in regulating genes associated with quorum sensing controlled bacterial virulence. This study was aimed to unveil the regulatory role of sRNA PA0730.1 on the expression of various traits of Pseudomonas aeruginosa linked to pathogenicity, with special emphasis on the growth, colony morphology, cell motility, biofilm formation, and the expression of diverse virulence factors. PA0730.1 sRNA was found to be upregulated both during planktonic stationary growth phase and at biofilm state of P. aeruginosa PAO1. PA0730.1 deleted strain showed significant growth retardation with increased doubling time. Overexpression of PA0730.1 led to enhanced motility and biofilm formation, while the ∆PA0730.1 strain displayed significant inhibition in motility and biofilm formation. Furthermore, PA0730.1 was found to regulate the synthesis of selected virulence factors of P. aeruginosa. These observations in PA0730.1+ and ∆PA0730.1 were found to be correlated with the PA0730.1-mediated repression of transcription regulators, mucA and rpoS, both at transcriptional and translational levels. The results suggest that PA0730.1 sRNA might be a promising target for developing new drug to counter P. aeruginosa pathogenesis, and could also help in RNA oligonucleotide based therapeutic research for formulating a novel therapeutant.

Green-synthesized silver nanoparticles from Zataria multiflora as a promising strategy to target quorum sensing and biofilms in Pseudomonas aeruginosa

The global challenge to human health is significantly heightened by the resistance of harmful bacteria to antimicrobial treatments. Given the limited advancement in developing new antimicrobial medications, exploring innovative strategies is imperative to tackle the challenge of resistance to multiple drugs. Furthermore, there is a growing emphasis on the environmentally friendly synthesis of nanoparticles with potent medicinal attributes, specifically those targeting virulence, to combat the rise of multidrug resistance. Focusing on the inhibition of virulence factors and biofilms influenced by quorum sensing has become a promising and novel strategy in the development of anti-infective drugs. An aqueous extract of Zataria multiflora leaves was used to create green-synthesized silver nanoparticles, or AgNPs. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and UV-visible absorption spectroscopy were used to characterize the AgNPs. The impact of AgNPs on the virulence factors and biofilms of Pseudomonas aeruginosa PAO1, mediated by quorum sensing, was assessed at concentrations below the minimum inhibitory concentration (sub-MIC). Sub-MIC concentrations of Green-synthesized AgNPs inhibited various P. aeruginosa virulence factors, including bacterial motility (89 % inhibition), pyocyanin production (81.48 % inhibition), pyoverdin production (55.80 % inhibition), elastase activity (87.43 % inhibition), exoprotease activity (75.60 % inhibition), and rhamnolipid production (71.28 % inhibition). Additionally, these AgNPs demonstrated 80 % inhibition of P. aeruginosa biofilms. The in vitro efficacy of green-synthesized AgNPs against P. aeruginosa can be utilized for the creation of alternative therapeutic agents for managing bacterial infections, particularly for topical application in cases such as wound infections. Additionally, they can be used for surface coating to inhibit the attachment of bacteria to medical devices.

Umbelliferone modulates the quorum sensing and biofilm of Gram - ve bacteria: in vitro and in silico investigations

In last two decades, the world has seen an exponential increase in the antimicrobial resistance (AMR), making the issue a serious threat to human health. The mortality caused by AMR is one of the leading causes of human death worldwide. Till the end of the twentieth century, a tremendous success in the discovery of new antibiotics was seen, but in last two decades, there is negligible progress in this direction. The increase in AMR combined with slow progress of antibiotic drug discovery has created an urgent demand to search for newer methods of intervention to combat infectious diseases. One of such approach is to look for biofilm and quorum sensing (QS) inhibitors. Plants are excellent source of wide class compounds that can be harnessed to look for the compounds with such properties. This study proves a broad-spectrum biofilm and QS inhibitory potential of umbelliferone. More than 85% reduction in violacein production Chromobacterium violaceum 12472 was found. All tested virulent traits of Pseudomonas aeruginosa PAO1 and Serratia marcescens MTCC 97 were remarkably inhibited that ranged from 56.62% to 86.24%. Umbelliferone also successfully prevented the biofilm of test bacteria at least by 67.68%. Umbelliferone interacted at the active site of many proteins of QS circuit, which led to the mitigation of virulent traits. The stable nature of complexes of umbelliferone with proteins further strengthens in vitro results. After examining the toxicological profile and other drug-like properties, umbelliferone could be potentially developed as new drug to target the infections caused by Gram - ve bacteria.Communicated by Ramaswamy H. Sarma.

Unraveling the molecular dynamics of Pseudomonas aeruginosa biofilms at the air-liquid interface

Aim: The aim of this study was to probe the dynamics of Pseudomonas aeruginosa PA14 air-liquid interface (ALI) biofilms over time through global proteomic analysis. Materials & methods: P. aeruginosa PA14 ALI biofilm samples, collected over 48-144 h, underwent differential expression analysis to identify varying proteins at each time point. Results: A consistent set of 778 proteins was identified, with variable expression over time. Upregulated proteins were mainly linked to 'amino acid transport and metabolism'. Biofilm-related pathways, including cAMP/Vfr and QS, underwent significant changes. Flagella were more influential than pili, especially in early biofilm development. Proteins associated with virulence, transporters and iron showed differential expression throughout. Conclusion: The findings enhance our understanding of ALI biofilm development.

Antimicrobial Activity of Trigonelline Hydrochloride Against Pseudomonas aeruginosa and Its Quorum-Sensing Regulated Molecular Mechanisms on Biofilm Formation and Virulence

Pseudomonas aeruginosa, a vivid biofilm-producing bacterium, is considered a dreadful opportunistic pathogen, and thus, management of biofilm-associated infections due to multidrug resistant strains by traditional drugs currently is of great concern. This study was aimed to assess the impact of trigonelline hydrochloride, a pyridine alkaloid, on P. aeruginosa PAO1, in search of an alternative therapeutant. The effect of trigonelline on colony morphology and motility was studied along with its role on biofilm and expression virulence factors. Trigonelline influenced the colony structure, motility, biofilm architecture, and the production of virulence factors in a dose-dependent manner. Alterations in quorum sending (QS)-regulated gene expression after treatment and molecular docking analysis for certain regulator proteins confirmed its effect on the QS-system network by affecting Las, Rhl, and Pqs signaling pathways and as possible molecular targets. Thus, trigonelline might be considered as a potential chemical lead to manage biofilm-associated pathogenesis or to develop other analogues with enhanced pharmacokinetic actions.

Sterically hindered phenolic derivatives: effect on the production of Pseudomonas aeruginosa virulence factors, high-throughput virtual screening and ADME properties prediction

Inhibition of quorum sensing is considered to be an effective strategy of control and treatment of a wide range of acute and persistent infections. Pseudomonas aeruginosa is an opportunistic bacterium with a high adaptation potential that contributes to healthcare-associated infections. In the present study, the effects of the synthesized hybrid structures bearing sterically hindered phenolic and heterocyclic moieties in a single scaffold on the production of virulence factors by P. aeruginosa were determined. It has been shown that the obtained compounds significantly reduce both pyocyanin and alginate production and stimulate the biosynthesis of siderophores in vitro, which may be attributed to their iron-chelating properties. The results of docking-based inverse high-throughput virtual screening indicate that transcription regulator LasR and Cu-transporter OPRC could be potential molecular targets for these compounds. Investigation of the impact small molecules exert on the molecular mechanisms of the production of bacterial virulence factors may pave the way for the design and development of novel antibacterial agents.

Attenuation of quorum sensing regulated virulence functions and biofilm of pathogenic bacteria by medicinal plant Artemisia annua and its phytoconstituent 1, 8-cineole

The emergence of multidrug resistance (MDR) in bacterial pathogens is a serious public health concern. A significant therapeutic target for MDR infections is the quorum sensing-regulated bacterial pathogenicity. Determining the anti-quorum sensing abilities of certain medicinal plants against bacterial pathogens as well as the in-silico interactions of particular bioactive phytocompounds with QS and biofilm-associated proteins were the objectives of the present study. In this study, 6 medicinal plants were selected based on their ethnopharmacological usage, screened for Anti-QS activity and Artemisia annua leaf extract (AALE) demonstrated pigment inhibitory activity against Chromobacterium violaceum CV12472. Further, the methanol active fraction significantly inhibited the virulence factors (pyocyanin, pyoverdine, rhamnolipid and swarming motility) of Pseudomonas aeruginosa PAO1 and Serratia marcescens MTCC 97 at respective sub-MICs. The inhibition of biofilm was determined using a microtiter plate test and scanning electron microscopy. Biofilm formation was impaired by 70%, 72% and 74% in P. aeruginosa, C. violaceum and S. marcescens, respectively at 0.5xMIC of the extract. The phytochemical content of the extract was studied using GC-MS and 1, 8-cineole was identified as major bioactive compound. Furthermore, 1, 8-cineole was docked with quorum sensing (QS) proteins (LasI, LasR, CviR, and rhlR) and biofilm proteins (PilY1 and PilT). In silico docking and dynamics simulations studies suggested interactions with QS-receptors CviR', LasI, LasR, and biofilm proteins PilY1, PilT for anti-QS activity. Further, 1, 8-cineole demonstrated 66% and 51% reduction in violacein production and biofilm formation, respectively to validate the findings of computational analysis. Findings of the present investigation suggests that 1, 8-cineole plays a crucial role in the QS and biofilm inhibitory activity demonstrated by Artemisia annua extract. RESEARCH HIGHLIGHTS: Artemisia annua leaf extract (AALE) methanol fraction demonstrated broad-spectrum QS and biofilm inhibition Scanning electron microscopy (SEM) confirmed biofilm inhibition Molecular docking and simulation studies suggested positive interactions of 1,8-cineol with QS-receptors and biofilm proteins.

Modulation of quorum sensing and biofilm of Gram-negative bacterial pathogens by Cinnamomum zeylanicum L

The development of antibiotic resistant microbial pathogens has become a global health threat and a major concern in modern medicine. The problem of antimicrobial resistance (AMR) has majorly arisen due to sub-judicious use of antibiotics in health care and livestock industry. A slow progress has been made in last two decades in discovery of new antibiotics. A new strategy in combatting AMR is to modulate or disarm the microbes for their virulence and pathogenicity. Plants are considered as promising source for new drugs against AMR pathogens. In this study, fraction-based screening of the Cinnamomum zeylanicum extract was performed followed by detailed investigation of antiquorum sensing and antibiofilm activities of the most active fraction that is, C. zeylanicum hexane fraction (CZHF). More than 75% reduction in violacein pigment of C. violaceum 12472 was overserved. CZHF successfully modulated the virulence of Pseudomonas aeruginosa PAO1 by 60.46%-78.35%. A similar effect was recorded against Serratia marcescens MTCC 97. A broad-spectrum inhibition of biofilm development was found in presence of sub-MICs of CZHF. The colonization of bacteria onto the glass coverslips was remarkably reduced apart from the reduction in exopolymeric substances. Alkaloids and terpenoids were found in CZHF. GC/MS analysis revealed the presence of cinnamaldehyde dimethyl acetal, 2-propenal, coumarin, and α-copaene as major phytocompounds. This study provides enough evidence to support potency of C. zeylanicum extract in targeting the virulence of Gram -ve pathogenic bacteria. The plant extract or active compounds can be developed as successful drugs after careful in vivo examination to target microbial infections. RESEARCH HIGHLIGHTS: Hexane fraction of Cinnamomum zeylanicum is active against QS and biofilms. The broad-spectrum antibiofilm activity was further confirmed by microscopic analysis. Dimethyl acetal, 2-propenal, coumarin, α-copaene, and so forth are major phytocompounds.

A gene network-driven approach to infer novel pathogenicity-associated genes: application to Pseudomonas aeruginosa PAO1

IMPORTANCE

We present here a new systems-level approach to decipher genetic factors and biological pathways associated with virulence and/or antibiotic treatment of bacterial pathogens. The power of this approach was demonstrated by application to a well-studied pathogen Pseudomonas aeruginosa PAO1. Our gene co-expression network-based approach unraveled known and unknown genes and their networks associated with pathogenicity in P. aeruginosa PAO1. The systems-level investigation of P. aeruginosa PAO1 helped identify putative pathogenicity and resistance-associated genetic factors that could not otherwise be detected by conventional approaches of differential gene expression analysis. The network-based analysis uncovered modules that harbor genes not previously reported by several original studies on P. aeruginosa virulence and resistance. These could potentially act as molecular determinants of P. aeruginosa PAO1 pathogenicity and responses to antibiotics.

Molecular insights into RmcA-mediated c-di-GMP consumption: Linking redox potential to biofilm morphogenesis in Pseudomonas aeruginosa

The ability of many bacteria to form biofilms contributes to their resilience and makes infections more difficult to treat. Biofilm growth leads to the formation of internal oxygen gradients, creating hypoxic subzones where cellular reducing power accumulates, and metabolic activities can be limited. The pathogen Pseudomonas aeruginosa counteracts the redox imbalance in the hypoxic biofilm subzones by producing redox-active electron shuttles (phenazines) and by secreting extracellular matrix, leading to an increased surface area-to-volume ratio, which favors gas exchange. Matrix production is regulated by the second messenger bis-(3',5')-cyclic-dimeric-guanosine monophosphate (c-di-GMP) in response to different environmental cues. RmcA (Redox modulator of c-di-GMP) from P. aeruginosa is a multidomain phosphodiesterase (PDE) that modulates c-di-GMP levels in response to phenazine availability. RmcA can also sense the fermentable carbon source arginine via a periplasmic domain, which is linked via a transmembrane domain to four cytoplasmic Per-Arnt-Sim (PAS) domains followed by a diguanylate cyclase (DGC) and a PDE domain. The biochemical characterization of the cytoplasmic portion of RmcA reported in this work shows that the PAS domain adjacent to the catalytic domain tunes RmcA PDE activity in a redox-dependent manner, by differentially controlling protein conformation in response to FAD or FADH2. This redox-dependent mechanism likely links the redox state of phenazines (via FAD/FADH2 ratio) to matrix production as indicated by a hyperwrinkling phenotype in a macrocolony biofilm assay. This study provides insights into the role of RmcA in transducing cellular redox information into a structural response of the biofilm at the population level. Conditions of resource (i.e. oxygen and nutrient) limitation arise during chronic infection, affecting the cellular redox state and promoting antibiotic tolerance. An understanding of the molecular linkages between condition sensing and biofilm structure is therefore of crucial importance from both biological and engineering standpoints.

Attenuation of biofilm and quorum sensing regulated virulence factors of an opportunistic pathogen Pseudomonas aeruginosa by phytofabricated silver nanoparticles

Green-synthesized nanoparticles provide an effective strategy for inhibiting microbial pathogenesis by affecting biofilm formation, quorum sensing (QS), and other surface properties of microorganisms. QS is a density-dependent communication signaling cascade that regulates biofilm formation and other pathogenic factors of Pseudomonas aeruginosa. In this context, the effect of phytofabricated silver nanoparticles (CC-AgNPs) synthesized using Cuphea carthagenensis extract on biofilm, QS, and QS-dependent virulence factors of P. aeruginosa were evaluated in this study. CC-AgNPs demonstrated significant attenuation of biofilm, QS, and QS-dependent virulence factors at sub-MICs. A significant inhibition of 88.39 ± 4.32 %, 79.64 ± 3.31 %, 73.07 ± 3.0 %, and 61.67 ± 1.5 % of biofilm formation, quorum sensing, pyocyanin, and LasB elastase, respectively was reported in the study at 20 μg/mL. The study also demonstrated a significant reduction of LasA Staphylolytic activity and 91.37 ± 1.05 % exoprotease production in comparison to untreated control. The lower concentrations of CC-AgNPs also demonstrated significant attenuation of biofilm and other virulence factors suggesting the strong potency of NPs against P. aeruginosa. XTT analysis reported the effect of CC-AgNPs on sessile cells of P. aeruginosa without impacting growth of planktonic cells at sub-MICs. Cell-proliferation study in human cell lines (HEK 293 and Caco-2 cells) demonstrated the safe nature of CC-AgNPs at tested concentrations. This study is novel in a way that environmentally friendly CC-AgNPs were used to inhibit QS at sub-MICs without killing the tested strains, therefore, could be developed as an anti-virulent drug to overcome biofilm and antimicrobial resistance problems.

The heme-responsive PrrH sRNA regulates Pseudomonas aeruginosa pyochelin gene expression

Pseudomonas aeruginosa is an opportunistic pathogen that requires iron for growth and virulence, yet this nutrient is sequestered by the innate immune system during infection. When iron is limiting, P. aeruginosa expresses the PrrF1 and PrrF2 small RNAs (sRNAs), which post-transcriptionally repress expression of nonessential iron-containing proteins, thus sparing this nutrient for more critical processes. The genes for the PrrF1 and PrrF2 sRNAs are arranged in tandem on the chromosome, allowing for the transcription of a longer heme-responsive sRNA, termed PrrH. While the functions of PrrF1 and PrrF2 have been extensively studied, the role of PrrH in P. aeruginosa physiology and virulence is not well understood. In this study, we performed transcriptomic and proteomic studies to identify the PrrH regulon. In shaking cultures, the pyochelin synthesis proteins were increased in two distinct prrH mutants compared to the wild type, while the mRNAs for these proteins were not affected by the prrH mutation. We identified complementarity between the PrrH sRNA and the sequence upstream of the pchE mRNA, suggesting the potential for PrrH to directly regulate the expression of genes for pyochelin synthesis. We further showed that pchE mRNA levels were increased in the prrH mutants when grown in static but not shaking conditions. Moreover, we discovered that controlling for the presence of light was critical for examining the impact of PrrH on pchE expression. As such, our study reports on the first likely target of the PrrH sRNA and highlights key environmental variables that will allow for future characterization of PrrH function. IMPORTANCE In the human host, iron is predominantly in the form of heme, which Pseudomonas aeruginosa can acquire as an iron source during infection. We previously showed that the iron-responsive PrrF small RNAs (sRNAs) are critical for mediating iron homeostasis during P. aeruginosa infection; however, the function of the heme-responsive PrrH sRNA remains unclear. In this study, we identified genes for pyochelin siderophore biosynthesis, which mediates uptake of inorganic iron, as a novel target of PrrH regulation. This study therefore highlights a novel relationship between heme availability and siderophore biosynthesis in P. aeruginosa.

Bacterial biofilm inhibitors: An overview

Bacteria that cause infectious diseases adopt biofilms as one of their most prevalent lifestyles. Biofilms enable bacteria to tolerate environmental stress and evade antibacterial agents. This bacterial defense mechanism has rendered the use of antibiotics ineffective for the treatment of infectious diseases. However, many highly drug-resistant microbes have rapidly emerged owing to such treatments. Different signaling mechanisms regulate bacterial biofilm formation, including cyclic dinucleotide (c-di-GMP), small non-coding RNAs, and quorum sensing (QS). A cell density-dependent phenomenon, QS is associated with c-di-GMP (a global messenger), which regulates gene expression related to adhesion, extracellular matrix production, the transition from the planktonic to biofilm stage, stability, pathogenicity, virulence, and acquisition of nutrients. The article aims to provide information on inhibiting biofilm formation and disintegrating mature/preformed biofilms. This treatment enables antimicrobials to target the free-living/exposed bacterial cells at lower concentrations than those needed to treat bacteria within the biofilm. Therefore, a complementary action of antibiofilm and antimicrobial agents can be a robust strategic approach to dealing with infectious diseases. Taken together, these molecules have broad implications for human health.

A phenazine-inspired framework for identifying biological functions of microbial redox-active metabolites

While the list of small molecules known to be secreted by environmental microbes continues to grow, our understanding of their in situ biological functions remains minimal. The time has come to develop a framework to parse the meaning of these "secondary metabolites," which are ecologically ubiquitous and have direct applications in medicine and biotechnology. Here, we focus on a particular subset of molecules, redox active metabolites (RAMs), and review the well-studied phenazines as archetypes of this class. We argue that efforts to characterize the chemical, physical and biological makeup of the microenvironments, wherein these molecules are produced, coupled with measurements of the molecules' basic chemical properties, will enable significant progress in understanding the precise roles of novel RAMs.

Ascorbic acid modulates the structure of the Pseudomonas aeruginosa virulence factor pyocyanin and ascorbic acid-furanone-30 combination facilitate biofilm disruption

The production of pyocyanin by Pseudomonas aeruginosa increases its virulence, fitness and biofilm formation. Pyocyanin is also a redox molecule and we hypothesize that ascorbic acid being an antioxidant will interact with pyocyanin. The main objective of this study was to investigate the potential interaction of ascorbic acid with pyocyanin, and also to investigate the impact of ascorbic acid in combination with Furanone-30 on quorum sensing and biofilm formation of P. aeruginosa. When incubated with ascorbic acid, hyperchromic and hypsochromic shifts in pyocyanin absorbance peaks at 385 nm and 695 nm were observed. In the presence of dehydroascorbic acid and citric acid, these shifts were absent, indicating that the intrinsic antioxidant property of ascorbic acid was probably essential in binding to pyocyanin. NMR spectroscopy showed shifts in ¹H NMR pyocyanin peaks between 8.2 to 5.8 ppm when incubated in the presence of ascorbic acid. Density Functional Theory (DFT) supported potential interactions between the -CH₂OH or -OH moieties of ascorbic acid with the -C=O moiety of pyocyanin. The pyocyanin-ascorbic acid complex impaired pyocyanin binding to DNA. Ascorbic acid combined with furanone-30 elevated quorum-sensing inhibition in P. aeruginosa, which was directly associated with significantly reduced P. aeruginosa virulence, adhesion, aggregation and biofilm formation and enhanced antibiotic-mediated bacterial killing. This study demonstrated that the antioxidant ascorbic acid directly binds to pyocyanin, modulates its structure and results in disruption of biofilm formation and associated tolerance to antibiotics.

Phytogenically Synthesized Zinc Oxide Nanoparticles (ZnO-NPs) Potentially Inhibit the Bacterial Pathogens: In Vitro Studies

The usefulness of nanoparticles (NPs) in biological applications, such as nanomedicine, is becoming more widely acknowledged. Zinc oxide nanoparticles (ZnO-NPs) are a type of metal oxide nanoparticle with an extensive use in biomedicine. Here, ZnO-NPs were synthesized using Cassia siamea (L.) leaf extract and characterized using state-of-the-art techniques; UV-vis spectroscopy, XRD, FTIR, and SEM. At sub-minimum inhibitory concentration (MIC) levels, the ability of ZnO@Cs-NPs to suppress quorum-mediated virulence factors and biofilm formation against clinical MDR isolates (Pseudomonas aeruginosa PAO1 and Chromobacterium violaceum MCC-2290) was tested. The ½MIC of ZnO@Cs-NPs reduced violacein production by C. violaceum. Furthermore, ZnO@Cs-NPs sub-MIC significantly inhibited virulence factors such aspyoverdin, pyocyanin, elastase, exoprotease, rhamnolipid, and the swimming motility of P. aeruginosa PAO1 by 76.9, 49.0, 71.1, 53.3, 89.5, and 60%, respectively. Moreover, ZnO@Cs-NPs also showed wide anti-biofilm efficacy, inhibiting a maximum of 67 and 56% biofilms in P. aeruginosa and C. violaceum, respectively. In addition, ZnO@Cs-NPs suppressed extra polymeric substances (EPS) produced by isolates. Additionally, under confocal microscopy, propidium iodide-stained cells of P. aeruginosa and C. violaceum show ZnO@Cs-NP-induced impairment in membrane permeability, revealing strong anti-bacterial efficacy. This research demonstrates that newly synthesized ZnO@Cs-NPs demonstrate a strong efficacy against clinical isolates. In a nutshell, ZnO@Cs-NPs can be used as an alternative therapeutic agent for managing pathogenic infections.

Advances in mechanisms and engineering of electroactive biofilms

Electroactive biofilms (EABs) are electroactive microorganisms (EAMs) encased in conductive polymers that are secreted by EAMs and formed by the accumulation and cross-linking of extracellular polysaccharides, proteins, nucleic acids, lipids, and other components. EABs are present in the form of multicellular aggregates and play a crucial role in bioelectrochemical systems (BESs) for diverse applications, including biosensors, microbial fuel cells for renewable bioelectricity production and remediation of wastewaters, and microbial electrosynthesis of valuable chemicals. However, naturally occurred EABs are severely limited owing to their low electrical conductivity that seriously restrict the electron transfer efficiency and practical applications. In the recent decade, synthetic biology strategies have been adopted to elucidate the regulatory mechanisms of EABs, and to enhance the formation and electrical conductivity of EABs. Based on the formation of EABs and extracellular electron transfer (EET) mechanisms, the synthetic biology-based engineering strategies of EABs are summarized and reviewed as follows: (i) Engineering the structural components of EABs, including strengthening the synthesis and secretion of structural elements such as polysaccharides, eDNA, and structural proteins, to improve the formation of biofilms; (ii) Enhancing the electron transfer efficiency of EAMs, including optimizing the distribution of c-type cytochromes and conducting nanowire assembly to promote contact-based EET, and enhancing electron shuttles' biosynthesis and secretion to promote shuttle-mediated EET; (iii) Incorporating intracellular signaling molecules in EAMs, including quorum sensing systems, secondary messenger systems, and global regulatory systems, to increase the electron transfer flux in EABs. This review lays a foundation for the design and construction of EABs for diverse BES applications.

DNA-functionalized carbon quantum dots for electrochemical detection of pyocyanin: A quorum sensing molecule in Pseudomonas aeruginosa

The electrochemical biosensing strategy for pyocyanin (PYO), a virulent quorum-sensing molecule responsible for Pseudomonas aeruginosa infections, was developed by mimicking its extracellular DNA interaction. Calf thymus DNA (ct-DNA) functionalized amine-containing carbon quantum dots (CQDs) were used as a biomimetic receptor for electrochemical sensing of PYO as low as 37 nM in real urine sample. The ct-DNA-based biosensor enabled the selective measurement of PYO in the presence of other interfering species. Calibration and validation of the PYO sensor platform were demonstrated in buffer solution (0-100 μM), microbial culture media (0-100 μM), artificial urine (0-400 μM), and real urine sample (0-250 μM). The sensor capability was successfully implemented for point-of-care (POC) detection of PYO release from Pseudomonas aeruginosa strains during lag and stationary phases. Cross-reactivity of the sensing platform was also tested in other bacterial species such as Bacillus subtilis, Escherichia coli, Klebsiella pneumoniae, Shigella dysenteriae, Staphylococcus aureus, and Streptococcus pneumoniae. Potential clinical implementation of the ct-DNA-based sensor was manifested in detecting the PYO in P. aeruginosa cultured baby diaper and sanitary napkin. Our results highlight that the newly developed ct-DNA-based sensing platform can be used as a potential candidate for real-time POC diagnosis of Pseudomonas aeruginosa infection in clinical samples.

Spectroelectrochemical behavior of parallel arrays of single vertically oriented Pseudomonas aeruginosa cells

Pseudomonas aeruginosa is a Gram-negative opportunistic human pathogen responsible for a number of healthcare-associated infection. It is currently difficult to assess single cell behaviors of P. aeruginosa that might contribute to acquisition of antibiotic resistance, intercellular communication, biofilm development, or virulence, because mechanistic behavior is inferred from ensemble collections of cells, thus averaging effects over a population. Here, we develop and characterize a device that can capture and trap arrays of single P. aeruginosa cells in individual micropores in order to study their behaviors using spectroelectrochemistry. Focused ion beam milling is used to fabricate an array of micropores in a Au/dielectric/Au/SiO₂-containing multilayer substrate, in which individual micropores are formed with dimensions that facilitate the capture of single P. aeruginosa cells in a predominantly vertical orientation. The bottom Au ring is then used as a working electrode to explore the spectroelectrochemical behavior of parallel arrays of individual P. aeruginosa cells. Application of step-potential or swept-potential waveforms produces changes in the fluorescence emission that can be imaged and correlated with applied potential. Arrays of P. aeruginosa cells typically exhibit three characteristic fluorescence behaviors that are sensitive to nutritional stress and applied potential. The device developed here enables the study of parallel collections of single bacterial cells with well-defined orientational order and should facilitate efforts to elucidate methods of bacterial communication and multidrug resistance at the single cell level.

Treatment with paeoniflorin increases lifespan of Pseudomonas aeruginosa infected Caenorhabditis elegans by inhibiting bacterial accumulation in intestinal lumen and biofilm formation

Paeoniflorin is one of the important components in Paeoniaceae plants. In this study, we used Caenorhabditis elegans as a model host and Pseudomonas aeruginosa as a bacterial pathogen to investigate the possible role of paeoniflorin treatment against P. aeruginosa infection in the host and the underlying mechanisms. Posttreatment with 1.25–10 mg/L paeoniflorin could significantly increase the lifespan of P. aeruginosa infected nematodes. After the infection, the P. aeruginosa colony-forming unit (CFU) and P. aeruginosa accumulation in intestinal lumen were also obviously reduced by 1.25–10 mg/L paeoniflorin treatment. The beneficial effects of paeoniflorin treatment in increasing lifespan in P. aeruginosa infected nematodes and in reducing P. aeruginosa accumulation in intestinal lumen could be inhibited by RNAi of pmk-1, egl-1, and bar-1. In addition, paeoniflorin treatment suppressed the inhibition in expressions of pmk-1, egl-1, and bar-1 caused by P. aeruginosa infection in nematodes, suggesting that paeoniflorin could increase lifespan of P. aeruginosa infected nematode by activating PMK-1, EGL-1, and BAR-1. Moreover, although treatment with 1.25–10 mg/L paeoniflorin did not show obvious anti-P. aeruginosa activity, the P. aeruginosa biofilm formation and expressions of related virulence genes (pelA, pelB, phzA, lasB, lasR, rhlA, and rhlC) were significantly inhibited by paeoniflorin treatment. Treatment with 1.25–10 mg/L paeoniflorin could further decrease the levels of related virulence factors of pyocyanin, elastase, and rhamnolipid. In addition, 2.5–10 mg/L paeoniflorin treatment could inhibit the swimming, swarming, and twitching motility of P. aeruginosa, and treatment with 2.5–10 mg/L paeoniflorin reduced the cyclic-di-GMP (c-di-GMP) level. Therefore, paeoniflorin treatment has the potential to extend lifespan of P. aeruginosa infected hosts by reducing bacterial accumulation in intestinal lumen and inhibiting bacterial biofilm formation.

Systematic Full-Cycle Engineering Microbial Biofilms to Boost Electricity Production in Shewanella oneidensis

Electroactive biofilm plays a crucial rule in the electron transfer efficiency of microbial electrochemical systems (MES). However, the low ability to form biofilm and the low conductivity of the formed biofilm substantially limit the extracellular electron transfer rate of microbial cells to the electrode surfaces in MES. To promote biofilm formation and enhance biofilm conductivity, we develop synthetic biology approach to systematically engineer Shewanella oneidensis, a model exoelectrogen, via modular manipulation of the full-cycle different stages of biofilm formation, namely, from initial contact, cell adhesion, and biofilm growth stable maturity to cell dispersion. Consequently, the maximum output power density of the engineered biofilm reaches 3.62 ± 0.06 W m-2, 39.3-fold higher than that of the wild-type strain of S. oneidensis, which, to the best our knowledge, is the highest output power density that has ever been reported for the biofilms of the genetically engineered Shewanella strains.

Next-generation interaction proteomics for quantitative Jumbophage-bacteria interaction mapping

Host-pathogen interactions (HPIs) are pivotal in regulating establishment, progression, and outcome of an infection. Affinity-purification mass spectrometry has become instrumental for the characterization of HPIs, however the targeted nature of exogenously expressing individual viral proteins has limited its utility to the analysis of relatively small pathogens. Here we present the use of co-fractionation mass spectrometry (SEC-MS) for the high-throughput analysis of HPIs from native viral infections of two jumbophages ( ϕ KZ and ϕ PA3) in Pseudomonas aeruginosa . This enabled the detection > 6000 unique host-pathogen and > 200 pathogen-pathogen interactions for each phage, encompassing > 50% of the phage proteome. Interactome-wide comparison across phages showed similar perturbed protein interactions suggesting fundamentally conserved mechanisms of phage predation within the KZ-like phage family. Prediction of novel ORFs revealed a ϕ PA3 complex showing strong structural and sequence similarity to ϕ KZ nvRNAp, suggesting ϕ PA3 also possesses two RNA polymerases acting at different stages of the infection cycle. We further expanded our understanding on the molecular organization of the virion packaged and injected proteome by identifying 23 novel virion components and 5 novel injected proteins, as well as providing the first evidence for interactions between KZ-like phage proteins and the host ribosome. To enable accessibility to this data, we developed PhageMAP, an online resource for network query, visualization, and interaction prediction ( https://phagemap.ucsf.edu/ ). We anticipate this study will lay the foundation for the application of co-fractionation mass spectrometry for the scalable profiling of hostpathogen interactomes and protein complex dynamics upon infection.

The biofilm matrix: multitasking in a shared space

The biofilm matrix can be considered to be a shared space for the encased microbial cells, comprising a wide variety of extracellular polymeric substances (EPS), such as polysaccharides, proteins, amyloids, lipids and extracellular DNA (eDNA), as well as membrane vesicles and humic-like microbially derived refractory substances. EPS are dynamic in space and time and their components interact in complex ways, fulfilling various functions: to stabilize the matrix, acquire nutrients, retain and protect eDNA or exoenzymes, or offer sorption sites for ions and hydrophobic substances. The retention of exoenzymes effectively renders the biofilm matrix an external digestion system influencing the global turnover of biopolymers, considering the ubiquitous relevance of biofilms. Physico-chemical and biological interactions and environmental conditions enable biofilm systems to morph into films, microcolonies and macrocolonies, films, ridges, ripples, columns, pellicles, bubbles, mushrooms and suspended aggregates - in response to the very diverse conditions confronting a particular biofilm community. Assembly and dynamics of the matrix are mostly coordinated by secondary messengers, signalling molecules or small RNAs, in both medically relevant and environmental biofilms. Fully deciphering how bacteria provide structure to the matrix, and thus facilitate and benefit from extracellular reactions, remains the challenge for future biofilm research.

The heme-responsive PrrH sRNA regulates Pseudomonas aeruginosa pyochelin gene expression

Pseudomonas aeruginosa is an opportunistic pathogen that requires iron for growth and virulence, yet this nutrient is sequestered by the innate immune system during infection. When iron is limiting, P. aeruginosa expresses the PrrF1 and PrrF2 small regulatory RNAs (sRNAs), which post-transcriptionally repress expression of non-essential iron-containing proteins thus sparing this nutrient for more critical processes. The genes for the PrrF1 and PrrF2 sRNAs are arranged in tandem on the chromosome, allowing for the transcription of a longer heme-responsive sRNA, termed PrrH. While the functions of PrrF1 and PrrF2 have been studied extensively, the role of PrrH in P. aeruginosa physiology and virulence is not well understood. In this study, we performed transcriptomic and proteomic studies to identify the PrrH regulon. In shaking cultures, the pyochelin synthesis proteins were increased in two distinct prrH mutants compared to wild type, while the mRNAs for these proteins were not affected by prrH mutation. We identified complementarity between the PrrH sRNA and sequence upstream of the pchE mRNA, suggesting potential for PrrH to directly regulate expression of genes for pyochelin synthesis. We further showed that pchE mRNA levels were increased in the prrH mutants when grown in static but not shaking conditions. Moreover, we discovered controlling for the presence of light was critical for examining the impact of PrrH on pchE expression. As such, our study reports on the first likely target of the PrrH sRNA and highlights key environmental variables that will allow for future characterization of PrrH function.

CRISPRi-Mediated Gene Suppression Reveals Putative Reverse Transcriptase Gene PA0715 to Be a Global Regulator of Pseudomonas aeruginosa

Purpose

Pseudomonas aeruginosa is a common pathogen of infection in burn and trauma patients, and multi-drug resistant P. aeruginosa has become an increasingly important pathogen. Essential genes are key to the development of novel antibiotics. The PA0715 gene is a novel unidentified essential gene that has attracted our interest as a potential antibiotic target. Our study aims to determine the exact role of PA0715 in cell physiology and bacterial pathogenicity, providing important clues for antibiotic development.

Patients and Methods

The shuttle vector pHERD20T containing an arabinose inducible promoter was used to construct the CRISPRi system. Alterations in cellular physiology and bacterial pathogenicity of P. aeruginosa PAO1 after PA0715 inhibition were characterized. High-throughput RNA-seq was performed to gain more insight into the mechanisms by which PA0715 regulates the vital activity of P. aeruginosa.

Results

We found that down-regulation of PA0715 significantly reduced PAO1 growth rate, motility and chemotaxis, antibiotic resistance, pyocyanin and biofilm production. In addition, PA0715 inhibition reduced the pathogenicity of PAO1 to the greater galleria mellonella larvae. Transcriptional profiling identified 1757 genes including those related to amino acid, carbohydrate, ketone body and organic salt metabolism, whose expression was directly or indirectly controlled by PA0715. Unexpectedly, genes involved in oxidative phosphorylation also varied with PA0715 levels, and these findings support a hitherto unrecognized critical role for PA0715 in oxidative respiration in P. aeruginosa.

Conclusion

We identified PA0715 as a global regulator of the metabolic network that is indispensable for the survival and reproduction of P. aeruginosa. Our results provide a basis for future studies of potential antibiotic targets for P. aeruginosa and offer new ideas for P. aeruginosa infection control.

Antibiofilm Activity of PEGylated Branched Polyethylenimine

Biofilm formation is an adaptive resistance mechanism that pathogens employ to survive in the presence of antimicrobials. Pseudomonas aeruginosa is an infectious Gram-negative bacterium whose biofilm allows it to withstand antimicrobial attack and threaten human health. Chronic wound healing is often impeded by P. aeruginosa infections and the associated biofilms. Previous findings demonstrate that 600 Da branched polyethylenimine (BPEI) can restore β-lactam potency against P. aeruginosa and disrupt its biofilms. Toxicity concerns of 600 Da BPEI are mitigated by covalent linkage with low-molecular-weight polyethylene glycol (PEG), and, in this study, PEGylated BPEI (PEG350-BPEI) was found exhibit superior antibiofilm activity against P. aeruginosa. The antibiofilm activity of both 600 Da BPEI and its PEG derivative was characterized with fluorescence studies and microscopy imaging. We also describe a variation of the colony biofilm model that was employed to evaluate the biofilm disruption activity of BPEI and PEG-BPEI.

Proteomic profiling spotlights the molecular targets and the impact of the natural antivirulent umbelliferone on stress response, virulence factors, and the quorum sensing network of Pseudomonas aeruginosa

Pseudomonas aeruginosa easily adapts to newer environments and acquires several genome flexibilities to overcome the effect of antibiotics during therapeutics, especially in cystic fibrosis patients. During adaptation to the host system, the bacteria employ various tactics including virulence factor production and biofilm formation to escape from the host immune system and resist antibiotics. Hence, identifying alternative strategies to combat recalcitrant pathogens is imperative for the successful elimination of drug-resistant microbes. In this context, this study portrays the anti-virulence efficacy of umbelliferone (UMB) against P. aeruginosa. UMB (7-hydroxy coumarin) is pervasively found among the plant family of Umbelliferae and Asteraceae. The UMB impeded biofilm formation in the P. aeruginosa reference strain and clinical isolates on polystyrene and glass surfaces at the concentration of 125 µg/ml. Global proteomic analysis of UMB-treated cells revealed the downregulation of major virulence-associated proteins such as RhlR, LasA, AlgL, FliD, Tpx, HtpG, KatA, FusA1, Tsf, PhzM, PhzB2, CarB, DctP, MtnA, and MscL. A functional interaction study, gene ontology, and KEGG pathway analysis revealed that UMB could modulate the global regulators, enzymes, co-factors, and transcription factors related to quorum sensing (QS), stress tolerance, siderophore production, motility, and microcolony formation. In vitro biochemical assays further affirmed the anti-virulence efficacy of UMB by reducing pyocyanin, protease, elastase, and catalase production in various strains of P. aeruginosa. Besides the antibiofilm activity, UMB-treated cells exhibited enhanced antibiotic susceptibility to various antibiotics including amikacin, kanamycin, tobramycin, ciprofloxacin, and cefotaxime. Furthermore, in vitro cytotoxicity analysis revealed the biocompatibility of UMB, and the IC₅₀ value was determined to be 249.85 µg/ml on the HepG2 cell line. Altogether, the study substantiates the anti-virulence efficacy of UMB against P. aeruginosa, and the proteomic analysis reveals the differential expression of the regulators related to QS, stress response, and motility factors.

Interplay between biofilm microenvironment and pathogenicity of Pseudomonas aeruginosa in cystic fibrosis lung chronic infection

Pseudomonas aeruginosa (PA) is a highly, if not the most, versatile microorganism capable of colonizing diverse environments. One of the niches in which PA is able to thrive is the lung of cystic fibrosis (CF) patients. Due to a genetic aberration, the lungs of CF-affected patients exhibit impaired functions, rendering them highly susceptible to bacterial colonization. Once PA attaches to the epithelial surface and transitions to a mucoid phenotype, the infection becomes chronic, and antibiotic treatments become inefficient. Due to the high number of affected people and the severity of this infection, CF-chronic infection is a well-documented disease. Still, numerous aspects of PA CF infection remain unclear. The scientific reports published over the last decades have stressed how PA can adapt to CF microenvironmental conditions and how its surrounding matrix of extracellular polymeric substances (EPS) plays a key role in its pathogenicity. In this context, it is of paramount interest to present the nature of the EPS together with the local CF-biofilm microenvironment. We review how the PA biofilm microenvironment interacts with drugs to contribute to the pathogenicity of CF-lung infection. Understanding why so many drugs are inefficient in treating CF chronic infection while effectively treating planktonic PA is essential to devising better therapeutic targets and drug formulations.

Anti-quorum sensing and biofilm inhibitory effect of some medicinal plants against gram-negative bacterial pathogens: in vitro and in silico investigations

Multidrug resistance (MDR) in pathogenic bacteria have become a major clinical issue. Quorum sensing regulated bacterial virulence is a promising key drug target for MDR infections. Therefore, the aim of the present work was to assess the anti-quorum sensing properties of selected medicinal plants against bacterial pathogens as well in silico interaction of selected bioactive phytocompounds with QS and biofilm-associated proteins. Based on the ethnopharmacological usage, 18 plants were selected using methanolic extract against Chromobacterium violaceum 12472. The most active extract (Acacia nilotica) was fractionated in increasing polarity solvents (n-hexane, chloroform and ethyl acetate) and tested for anti-QS activity. The most active fraction i.e. ethyl acetate fraction was evaluated for their activity at sub-MICs against QS-associated virulence factors of Pseudomonas aeruginosa PAO1 and Serretia marcescens MTCC 97. Microtiter plate assay and light microscopy was used to determine inhibition of biofilm. Phytochemicals of the ethyl acetate fraction were analysed by GC/MS and LC/MS. Phytocompounds were docked with QS (LasI, LasR, CviR, and rhlR) and biofilm proteins (PilY1 and PilT) using Auto dock vina. The MIC of ethyl acetate fraction determined was 250, 500, and 1000 μg/ml against C. violaceum 12472, P. aeruginosa PAO1, and S. marcescens MTCC97 respectively. At sub-MICs QS regulated virulence factors production and inhibited biofilms broadly (more than 50 percent). GC/MS detected the major bioactive compound benzoic acid, 3,4,5-trihydroxy-, methyl ester (61.24 %) and LC-MS detected Retronecine for the first time in A. nilotica pods. In silico, dehydroabietic acid occupied the same cavity as its antagonist in the CviR ligand binding domain. Also, betulin and epicatechin gallate interact with biofilm proteins PilY1 and PilT, preventing biofilm formation. The findings suggest that the phytochemicals of A. nilotica pod could be exploited as an anti-QS agent against Gram-negative pathogens. To discover therapeutic efficacy of standardised bioactive extract/phytochemicals must be tested under in vivo condition.

Effect of Biogenic Silver Nanoparticles on the Quorum-Sensing System of Pseudomonas aeruginosa PAO1 and PA14

The increase in multidrug-resistant microorganisms represents a global threat requiring the development novel strategies to fight bacterial infection. This study aimed to assess the effect of silver nanoparticles (bio-AgNPs) on bacterial growth, biofilm formation, production of virulence factors, and expression of genes related to the quorum-sensing (QS) system of P. aeruginosa PAO1 and PA14. Biofilm formation and virulence assays were performed with bio-AgNPs. RT-qPCR was carried out to determine the effect of bio-AgNPs on the QS regulatory genes lasI, lasR, rhlI, rhlR, pqsA, and mvfR. Bio-AgNPs had an MIC value of 62.50 μM, for both strains. Phenotypic and genotypic assays were carried out using sub-MIC values. Experimental results showed that treatment with sub-MICs of bio-AgNPs reduced (p < 0.05) the motility and rhamnolipids and elastase production in P. aeruginosa PAO1. In PA14, bio-AgNPs stimulated swarming and twitching motilities as well as biofilm formation and elastase and pyocyanin production. Bio-AgNP treatment increased (p < 0.05) the expression of QS genes in PAO1 and PA14. Despite the different phenotypic behaviors in both strains, both showed an increase in the expression of QS genes. Demonstrating that the bio-AgNPs acted in the induction of regulation. The possible mechanism underlying the action of bio-AgNPs involves the induction of the rhl and/or pqs system of PAO1 and of the las and/or pqs system of PA14. These results suggest that exposure to low concentrations of bio-AgNPs may promote the expression of QS regulatory genes in P. aeruginosa, consequently inducing the production of virulence factors such as elastase, pyocyanin, and biofilms.

Superior inhibition of virulence and biofilm formation of Pseudomonas aeruginosa PAO1 by phyto-synthesized silver nanoparticles through anti-quorum sensing activity

Quorum sensing (QS)-regulated bacterial biofilm formation is a crucial issue in causing resistance against existing antibiotics. There is a considerable necessity to disrupt the interrelationship between bacterial QS, virulence, and biofilm formation. Disabling QS could be a novel tactic of great clinical importance. Here, we biosynthesized silver nanoparticles (Ka-AgNPs) using the aqueous leaf extract of Koelreuteria paniculata as a reducing and capping agents. The UV-Vis spectroscopy confirmed the synthesis of Ka-AgNPs as a characterization peak observed at 420 nm. TEM image revealed the spherical shape distribution of Ka-AgNPs with average particle size of 30.0 ± 5 nm. The anti-QS activity of Ka-AgNPs was tested against a bio-indicator bacterium Chromobacterium violaceum 12472 and a multi-drug resistant model strain of Pseudomonas aeruginosa (PAO1). The results demonstrated that the Ka-AgNPs superiorly inhibited QS-regulated virulence factors in PAO1 without affecting cell viability compared to chemically synthesized AgNPs (Cs-AgNPs). The Ka-AgNPs effectively suppressed the formation of biofilm of PAO1. RT-PCR results revealed that the Ka-AgNPs inhibited the expression of QS-regulated virulence genes of PAO1. These results suggest that the phyto-synthesized AgNPs could be used as promising anti-infective agents for treating drug-resistant P. aeruginosa.

Neutralization of ionic interactions by dextran-based single-chain nanoparticles improves tobramycin diffusion into a mature biofilm

The extracellular matrix protects biofilm cells by reducing diffusion of antimicrobials. Tobramycin is an antibiotic used extensively to treat P. aeruginosa biofilms, but it is sequestered in the biofilm periphery by the extracellular negative charge matrix and loses its efficacy significantly. Dispersal of the biofilm extracellular matrix with enzymes such as DNase I is another promising therapy that enhances antibiotic diffusion into the biofilm. Here, we combine the charge neutralization of tobramycin provided by dextran-based single-chain polymer nanoparticles (SCPNs) together with DNase I to break the biofilm matrix. Our study demonstrates that the SCPNs improve the activity of tobramycin and DNase I by neutralizing the ionic interactions that keep this antibiotic in the biofilm periphery. Moreover, the detailed effects and interactions of nanoformulations with extracellular matrix components were revealed through time-lapse imaging of the P. aeruginosa biofilms by laser scanning confocal microscopy with specific labeling of the different biofilm components.

Targeting the Holy Triangle of Quorum Sensing, Biofilm Formation, and Antibiotic Resistance in Pathogenic Bacteria

Chronic and recurrent bacterial infections are frequently associated with the formation of biofilms on biotic or abiotic materials that are composed of mono- or multi-species cultures of bacteria/fungi embedded in an extracellular matrix produced by the microorganisms. Biofilm formation is, among others, regulated by quorum sensing (QS) which is an interbacterial communication system usually composed of two-component systems (TCSs) of secreted autoinducer compounds that activate signal transduction pathways through interaction with their respective receptors. Embedded in the biofilms, the bacteria are protected from environmental stress stimuli, and they often show reduced responses to antibiotics, making it difficult to eradicate the bacterial infection. Besides reduced penetration of antibiotics through the intricate structure of the biofilms, the sessile biofilm-embedded bacteria show reduced metabolic activity making them intrinsically less sensitive to antibiotics. Moreover, they frequently express elevated levels of efflux pumps that extrude antibiotics, thereby reducing their intracellular levels. Some efflux pumps are involved in the secretion of QS compounds and biofilm-related materials, besides being important for removing toxic substances from the bacteria. Some efflux pump inhibitors (EPIs) have been shown to both prevent biofilm formation and sensitize the bacteria to antibiotics, suggesting a relationship between these processes. Additionally, QS inhibitors or quenchers may affect antibiotic susceptibility. Thus, targeting elements that regulate QS and biofilm formation might be a promising approach to combat antibiotic-resistant biofilm-related bacterial infections.

Nutrient Sensing and Biofilm Modulation: The Example of L-arginine in Pseudomonas

Bacterial biofilm represents a multicellular community embedded within an extracellular matrix attached to a surface. This lifestyle confers to bacterial cells protection against hostile environments, such as antibiotic treatment and host immune response in case of infections. The Pseudomonas genus is characterised by species producing strong biofilms difficult to be eradicated and by an extraordinary metabolic versatility which may support energy and carbon/nitrogen assimilation under multiple environmental conditions. Nutrient availability can be perceived by a Pseudomonas biofilm which, in turn, readapts its metabolism to finally tune its own formation and dispersion. A growing number of papers is now focusing on the mechanism of nutrient perception as a possible strategy to weaken the biofilm barrier by environmental cues. One of the most important nutrients is amino acid L-arginine, a crucial metabolite sustaining bacterial growth both as a carbon and a nitrogen source. Under low-oxygen conditions, L-arginine may also serve for ATP production, thus allowing bacteria to survive in anaerobic environments. L-arginine has been associated with biofilms, virulence, and antibiotic resistance. L-arginine is also a key precursor of regulatory molecules such as polyamines, whose involvement in biofilm homeostasis is reported. Given the biomedical and biotechnological relevance of biofilm control, the state of the art on the effects mediated by the L-arginine nutrient on biofilm modulation is presented, with a special focus on the Pseudomonas biofilm. Possible biotechnological and biomedical applications are also discussed.

The Small RNA AmiL Regulates Quorum Sensing-Mediated Virulence in Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa is an opportunistic and nosocomial pathogen of humans with hundreds of its virulence factors regulated by quorum sensing (QS) system. Small noncoding RNAs (sRNAs) are also key regulators of bacterial virulence. However, the QS regulatory sRNAs (Qrrs) that have been characterized in P. aeruginosa are still largely unknown. Here, sRNA AmiL (PA3366.1) in the amiEBCRS operon of PAO1 was identified as a novel Qrr by transcriptome sequencing (RNA-Seq). The expression of AmiL was negatively regulated by the las or rhl system, of which RhlR probably inhibited its transcription. AmiL deletion mutant and overexpressing strains were constructed in PAO1. Broad phenotypic changes were found, including reduced pyocyanin synthesis, elastase activity, biofilm formation, hemolytic activity, and cytotoxicity, as well as increased rhamnolipid production and swarming motility. AmiL appears to be a new regulator that influences diverse QS-mediated virulence. Furthermore, AmiL directly targeted PhzC, a key member of pyocyanin synthesis. AmiL also negatively regulated lasI expression in the early growth of PAO1, but predominantly increased rhlI expression and C4-HSL production in the middle and late stages. Therefore, a novel QS-sRNA signaling cascade of las/rhl (RhlR)-AmiL-PhzC/las/rhl was demonstrated, and it will help to shed new light on the virulence regulatory network of P. aeruginosa PAO1.

IMPORTANCEP. aeruginosa is a common nosocomial pathogen that causes diverse opportunistic infections in humans. The virulence crucial for infection is mainly regulated by QS. Small noncoding RNAs (sRNAs) involved in virulence regulation have also been identified in many bacteria. Recently, there is a growing interest in the new sRNA species, QS regulatory sRNAs (Qrrs). Understanding Qrrs-mediated regulation in P. aeruginosa virulence is therefore important to combat infection. In this study, a previously uncharacterized sRNA AmiL in PAO1 has been identified as a novel Qrr. It has been found to influence diverse QS-mediated virulence factors including pyocyanin, elastase, rhamnolipid, and hemolysin, as well as biofilm formation, swarming motility, and cytotoxicity. Furthermore, PhzC essential for pyocyanin synthesis was a direct target of AmiL. QS gene expression and C4-HSL production were also regulated by AmiL. This study provides insights into the roles of Qrr AmiL in modulating P. aeruginosa virulence.

The effects of LL-37 on virulence factors related to the quorum sensing system of Pseudomonas aeruginosa

Background

Antimicrobial peptides (AMPs) have shown promise in the treatment of multi-resistant pathogens. It was therefore of interest to analyze the effects of the AMP LL-37 on the regulation of several virulence factors related to the quorum sensing (QS) system of Pseudomonas aeruginosa (P. aeruginosa) in vitro.

Methods

The minimum inhibitory concentration (MIC) was evaluated by the micro broth dilution method. The expression of QS-related and QS-regulated virulence factor genes was also evaluated. Exotoxin A activity was measured with the nicotinamide adenine dinucleotide (NAD) (Coenzyme I) method; Elastase activity was detected with the elastin-Congo red (ECR) method; Pyocyanin detection was performed using the chloroform extraction method. The effects of LL-37 were assessed by measuring the expression changes of the virulence protein-encoding genes of the strains with quantitative polymerase chain reaction (PCR).

Results

The MIC of LL-37 against both P. aeruginosa reference strain (ATCC 15692 PAO1) and PA-ΔlasI/rhII was therefore determined to be 256 µg/mL. LL-37 at sub-minimum inhibitory concentrations (sub-MICs) had no significant effects on P. aeruginosa bacterial growth (P>0.05), but significantly downregulated the expression of all 3 virulence factors.

Conclusions

Interestingly, this effect appeared to be dose-related. These findings suggest that LL-37 could be a potential candidate for QS inhibition against bacterial infection and may have significant clinical potential in the treatment of P. aeruginosa biofilms.

Antimicrobial and Anti-inflammatory Gallium-Defensin Surface Coatings for Implantable Devices

Emerging and re-emerging infections are a global threat driven by the development of antimicrobial resistance due to overuse of antimicrobial agents and poor infection control practices. Implantable devices are particularly susceptible to such infections due to the formation of microbial biofilms. Furthermore, the introduction of implants into the body often results in inflammation and foreign body reactions. The antimicrobial and anti-inflammatory properties of gallium (Ga) have been recognized but not yet utilized effectively to improve implantable device integration. Furthermore, defensin (De, hBD-1) has potent antimicrobial activity in vivo as part of the innate immune system; however, this has not been demonstrated as successfully when used in vitro. Here, we combined Ga and De to impart antimicrobial activity and anti-inflammatory properties to polymer-based implantable devices. We fabricated polylactic acid films, which were modified using Ga implantation and subsequently functionalized with De. Ga-ion implantation increased surface roughness and increased stiffness. Ga implantation and defensin immobilization both independently and synergistically introduced antimicrobial activity to the surfaces, significantly reducing total live bacterial biomass. We demonstrated, for the first time, that the antimicrobial effects of De were unlocked by its surface immobilization. Ga implantation of the surface also resulted in reduced foreign body giant cell formation and expression of proinflammatory cytokine IL-1β. Cumulatively, the treated surfaces were able to kill bacteria and reduce inflammation in comparison to the untreated control. These innovative surfaces have the potential to prevent biofilm formation without inducing cellular toxicity or inflammation, which is highly desired for implantable device integration.

Halogenated Dihydropyrrol-2-One Molecules Inhibit Pyocyanin Biosynthesis by Blocking the Pseudomonas Quinolone Signaling System

Quorum-sensing (QS) systems of Pseudomonas aeruginosa are involved in the control of biofilm formation and virulence factor production. The current study evaluated the ability of halogenated dihydropyrrol-2-ones (DHP) (Br (4a), Cl (4b), and F (4c)) and a non-halogenated version (4d) to inhibit the QS receptor proteins LasR and PqsR. The DHP molecules exhibited concentration-dependent inhibition of LasR and PqsR receptor proteins. For LasR, all compounds showed similar inhibition levels. However, compound 4a (Br) showed the highest decrease (two-fold) for PqsR, even at the lowest concentration (12.5 µg/mL). Inhibition of QS decreased pyocyanin production amongst P. aeruginosa PAO1, MH602, ATCC 25619, and two clinical isolates (DFU-53 and 364707). In the presence of DHP, P. aeruginosa ATCC 25619 showed the highest decrease in pyocyanin production, whereas clinical isolate DFU-53 showed the lowest decrease. All three halogenated DHPs also reduced biofilm formation by between 31 and 34%. The non-halogenated compound 4d exhibited complete inhibition of LasR and had some inhibition of PqsR, pyocyanin, and biofilm formation, but comparatively less than halogenated DHPs.

Beneficial biofilms: A mini-review of strategies to enhance biofilm formation for biotechnological applications

The capacity of bacteria to form biofilms is an important trait for their survival and persistence. Biofilms occur naturally in soil and aquatic environments, are associated with animals ranging from insects to humans and are also found in built environments. They are typically encountered as a challenge in healthcare, food industry, and water supply ecosystems. In contrast, they are known to play a key role in the industrial production of commercially valuable products, environmental remediation processes, and in microbe-catalysed electrochemical systems for energy and resource recovery from wastewater. While there are many recent articles on biofilm control and removal, review articles on promoting biofilm growth for biotechnological applications are unavailable. Biofilm formation is a tightly regulated response to perturbations in the external environment. The multi-stage process, mediated by an assortment of proteins and signaling systems, involves the attachment of bacterial cells to a surface followed by their aggregation in a matrix of extracellular polymeric substances. Biofilms can be promoted by altering the external environment in a controlled manner, supplying molecules that trigger the aggregation of cells and engineering genes associated with biofilm development. This mini-review synthesizes findings from studies that have described such strategies and highlights areas needing research attention.

The Development of Vaccines from Synthetic Tumor-Associated Mucin Glycopeptides and their Glycosylation-Dependent Immune Response

Tumor-associated carbohydrate antigens are overexpressed as altered-self in most common epithelial cancers. Their glycosylation patterns differ from those of healthy cells, functioning as an ID for cancer cells. Scientists have been developing anti-cancer vaccines based on mucin glycopeptides, yet the interplay of delivery system, adjuvant and tumor associated MUC epitopes in the induced immune response is not well understood. The current state of the art suggests that the identity, abundancy and location of the glycans on the MUC backbone are all key parameters in the cellular and humoral response. This review shares lessons learned by us in over two decades of research in glycopeptide vaccines. By bridging synthetic chemistry and immunology, we discuss efforts in designing synthetic MUC1/4/16 vaccines and focus on the role of glycosylation patterns. We provide a brief introduction into the mechanisms of the immune system and aim to promote the development of cancer subunit vaccines.

Effects of Itxasol© Components on Gene Expression in Bacteria Related to Infections of the Urinary Tract and to the Inflammation Process

Urinary tract infections (UTIs) represent a health problem of the first magnitude since they affect large segments of the population, cause increased mortality and comorbidity, and have a high incidence of relapse. Therefore, UTIs cause a major socioeconomic concern. Current antibiotic treatments have various limitations such as the appearance of resistance to antibiotics, nephrotoxicity, and side effects such as gastrointestinal problems including microbiota alterations that contribute to increasing antibiotic resistance. In this context, Itxasol© has emerged, approved as an adjuvant for the treatment of UTIs. Designed with biomimetic principles, it is composed of arbutin, umbelliferon, and N-acetyl cysteine. In this work, we review the activities of these three compounds concerning the changes they produce in the expression of bacterial genes and those related to inflammation as well as assess how they are capable of affecting the DNA of bacteria and fungi.

Bacterial Responses to Iron Withholding by Calprotectin

Iron (Fe) plays important roles in both essential cellular processes and virulence pathways for many bacteria. Consequently, Fe withholding by the human innate immune system is an effective form of defense against bacterial infection. In this Perspective, we review recent studies that have established a foundation for our understanding of the impact of the metal-sequestering host defense protein calprotectin (CP) on bacterial Fe homeostasis. We also discuss two recently uncovered strategies for bacterial adaptation to Fe withholding by CP. Together, these studies provide insight into how Fe sequestration by CP affects bacterial pathogens that include Pseudomonas aeruginosa, Acinetobacter baumannii, and Staphylococcus aureus. Overall, recent studies suggest that Fe withholding by CP may have implications for bacterial survival and virulence in the host, and further explorations that directly address this possibility present an important area for discovery.

6-Methylcoumarin attenuates quorum sensing and biofilm formation in Pseudomonas aeruginosa PAO1 and its applications on solid surface coatings with polyurethane

Quorum sensing mediated biofilm formation has a major role in modern therapeutics due to adherence of cells on the solid surface. Here, we have developed a stable polyurethane blend with a 6-methylcoumarin (6-MC) composite that showed significant antibiofilm activity. The 6-MC was found to prominently inhibit P. aeruginosa PAO1 biofilm formation at 125 μg/ml and was able to inhibit various virulence factors such as pyocyanin, siderophore, exopolysaccharide, elastase and proteases, including motility of the bacteria. In addition, 6-MC was found functionally active in saving the C. elegans from P. aeruginosa PAO1 infection. Moreover, docking studies of different activator proteins correlate well with in vitro and in vivo results. To enhance this biological activity, 6-MC was blended with polyurethane, which also revealed superior antibiofilm activity on plastic and glass surfaces compared to a polyurethane coating. Therefore, the 6-MC could be used to combat P. aeruginosa infection for effective treatment and antibiofilm applications on solid surfaces through polyurethane blending and subsequent film fabrication strategies. KEY POINTS: • 6-Methylcoumarin significantly inhibits P. aeruginosa PAO1 biofilm • 6-MC was found functionally active in saving the C. elegans from PAO1 infection • 6-MC and polyurethane blend showed superior antibiofilm activity.

Revisiting the virulence hallmarks of Pseudomonas aeruginosa: a chronicle through the perspective of quorum sensing

Pseudomonas aeruginosa is an opportunistic pathogen and the leading cause of mortality among immunocompromised patients in clinical setups. The hallmarks of virulence in P. aeruginosa encompass six biologically competent attributes that cumulatively drive disease progression in a multistep manner. These multifaceted hallmarks lay the principal foundation for rationalizing the complexities of pseudomonal infections. They include factors for host colonization and bacterial motility, biofilm formation, production of destructive enzymes, toxic secondary metabolites, iron-chelating siderophores and toxins. This arsenal of virulence hallmarks is fostered and stringently regulated by the bacterial signalling system called quorum sensing (QS). The central regulatory functions of QS in controlling the timely expression of these virulence hallmarks for adaptation and survival drive the disease outcome. This review describes the intricate mechanisms of QS in P. aeruginosa and its role in shaping bacterial responses, boosting bacterial fitness. We summarize the virulence hallmarks of P. aeruginosa, relating them with the QS circuitry in clinical infections. We also examine the role of QS in the development of drug resistance and propose a novel antivirulence therapy to combat P. aeruginosa infections. This can prove to be a next-generation therapy that may eventually become refractory to the use of conventional antimicrobial treatments.

Disruption of the Pseudomonas aeruginosa Tat system perturbs PQS-dependent quorum sensing and biofilm maturation through lack of the Rieske cytochrome bc1 sub-unit

Extracellular DNA (eDNA) is a major constituent of the extracellular matrix of Pseudomonas aeruginosa biofilms and its release is regulated via pseudomonas quinolone signal (PQS) dependent quorum sensing (QS). By screening a P. aeruginosa transposon library to identify factors required for DNA release, mutants with insertions in the twin-arginine translocation (Tat) pathway were identified as exhibiting reduced eDNA release, and defective biofilm architecture with enhanced susceptibility to tobramycin. P. aeruginosa tat mutants showed substantial reductions in pyocyanin, rhamnolipid and membrane vesicle (MV) production consistent with perturbation of PQS-dependent QS as demonstrated by changes in pqsA expression and 2-alkyl-4-quinolone (AQ) production. Provision of exogenous PQS to the tat mutants did not return pqsA, rhlA or phzA1 expression or pyocyanin production to wild type levels. However, transformation of the tat mutants with the AQ-independent pqs effector pqsE restored phzA1 expression and pyocyanin production. Since mutation or inhibition of Tat prevented PQS-driven auto-induction, we sought to identify the Tat substrate(s) responsible. A pqsA::lux fusion was introduced into each of 34 validated P. aeruginosa Tat substrate deletion mutants. Analysis of each mutant for reduced bioluminescence revealed that the primary signalling defect was associated with the Rieske iron-sulfur subunit of the cytochrome bc₁ complex. In common with the parent strain, a Rieske mutant exhibited defective PQS signalling, AQ production, rhlA expression and eDNA release that could be restored by genetic complementation. This defect was also phenocopied by deletion of cytB or cytC₁. Thus, either lack of the Rieske sub-unit or mutation of cytochrome bc₁ genes results in the perturbation of PQS-dependent autoinduction resulting in eDNA deficient biofilms, reduced antibiotic tolerance and compromised virulence factor production.

Pseudomonas aeruginosa is a highly adaptable human pathogen responsible for causing chronic biofilm-associated infections. Biofilms are highly refractory to host defences and antibiotics and thus difficult to eradicate. The biofilm extracellular matrix incorporates extracellular DNA (eDNA). This stabilizes biofilm architecture and helps confer tolerance to antibiotics. Since mechanisms that control eDNA release are not well understood, we screened a P. aeruginosa mutant bank for strains with defects in eDNA release and discovered a role for the twin-arginine translocation (Tat) pathway that exports folded proteins across the cytoplasmic membrane. Perturbation of the Tat pathway resulted in defective biofilms susceptible to antibiotic treatment as a consequence of perturbed pseudomonas quinolone (PQS) signalling. This resulted in the failure to produce or release biofilm components including eDNA, phenazines and rhamnolipids as well as microvesicles. Furthermore, we discovered that perturbation of PQS signalling was a consequence of the inability of tat mutants to translocate the Rieske subunit of the cytochrome bc₁ complex involved in electron transfer and energy transduction. Given the importance of PQS signalling and the Tat system to virulence and biofilm maturation in P. aeruginosa, our findings underline the potential of the Tat system as a drug target for novel antimicrobial agents.

Plumbagin inhibits quorum sensing-regulated virulence and biofilms of Gram-negative bacteria: in vitro and in silico investigations

The global rise in antimicrobial resistance and lack of discovery of new antimicrobials have created serious concerns. Targeting quorum sensing (QS) and biofilms of pathogenic bacteria is considered a promising approach in antimicrobial drug discovery. This study explored the inhibitory effect of plumbagin against biofilms and QS of Chromobacterium violaceum, Serratia marcescens and Pseudomonas aeruginosa. Violacein production in C. violaceum 12472 was reduced by >80%. The virulent traits of P. aeruginosa PAO1 such as pyocyanin, rhamnolipid and proteases were also inhibited at sub-minimum inhibitory concentrations. Moreover, the biofilms of the test bacteria were reduced by 56-70%. Plumbagin reduced the bacterial adherence and colonization on solid surface. Computational studies gave closer insights regarding the possible modes of action. Molecular dynamics simulations revealed that the protein complexes were quite stable under physiological conditions. This study provides both experimental and computational evidence regarding the efficacy of plumbagin against biofilms and the QS-controlled virulence factors of Gram-negative bacteria.

Coumarin Exhibits Broad-Spectrum Antibiofilm and Antiquorum Sensing Activity against Gram-Negative Bacteria: In Vitro and In Silico Investigation

Quorum sensing (QS) and biofilm inhibition are recognized as the novel drug targets for the broad-spectrum anti-infective strategy to combat the infections caused by drug-resistant bacterial pathogens. Many compounds from medicinal plants have been found to demonstrate anti-infective activity. However, broad-spectrum anti-QS and antibiofilm efficacy and their mode of action are poorly studied. In this study, the efficacy of coumarin was tested against QS-regulated virulent traits of Gram-negative bacteria. Coumarin inhibited the production of violacein pigment in Chromobacterium violaceum 12472 by 64.21%. Similarly, there was 87.25, 70.05, 76.07, 58.64, 48.94, and 81.20% inhibition of pyocyanin, pyoverdin, and proteolytic activity, lasB elastase activity, swimming motility, and rhamnolipid production, respectively, in Pseudomonas aeruginosa PAO1. All tested virulence factors of Serratia marcescens MTCC 97 were also suppressed by more than 50% at the highest sub-minimum inhibitory concentration. Moreover, the biofilms of bacterial pathogens were also inhibited in a dose-dependent manner. Molecular docking and molecular dynamics (MD) simulation gave insights into the possible mode of action. The binding energy obtained by docking studies ranged from -5.7 to -8.1 kcal mol^-1. Coumarin was found to be docked in the active site of acylhomoserine lactone (AHL) synthases and regulatory proteins of QS. MD simulations further supported the in vitro studies where coumarin formed a stable complex with the tested proteins. The secondary structure of all proteins showed a negligible change in the presence of coumarin. Computational studies showed that the possible mechanisms of anti-QS activity were the inhibition of AHL synthesis, antagonization of QS-regulatory proteins, and blocking of the receptor proteins. The findings of this study clearly highlight the potency of coumarin against the virulence factors of Gram-negative bacterial pathogens that may be developed as an effective inhibitor of QS and biofilms.

Interference of quorum sensing regulated bacterial virulence factors and biofilms by Plumbago zeylanica extract

There has been tremendous spread of antimicrobial resistance globally, mainly due to the excessive and unnecessary use of antibiotics, making the situation alarming. This has created a need for the development of alternative strategies to selectively target the bacterial pathogenicity without exerting selection pressure for the development of antimicrobial resistance. Targeting quorum sensing (QS)-mediated virulence and biofilms by nontoxic natural products is gaining importance as new control strategy to combat the virulence and biofilms of pathogenic bacteria. In this study, the crude extract of Plumbago zeylanica was fractioned in different solvents using liquid-liquid partitioning to obtain the most bioactive fraction. The inhibitory effect of the bioactive extract of P. zeylanica on QS at sub-minimum inhibitory concentrations (MICs) was studied against Chromobacterium violaceum 12472, Pseudomonas aeruginosa PAO1, and Serratia marcescens MTCC 97. Biofilm inhibition was studied using microtiter plate assay, scanning electron microscopy, and confocal laser scanning microscopy. Major phytocompounds detected were cinnamaldehyde dimethyl acetal, plumbagin, asarone, 4-chromanol, phthalic acid, palmitic acid, ergost-5-en-3-ol, stigmasterol, and β-sitosterol. The violacein production in C. violaceum 12472 was reduced by >80% in the presence of P. zeylanica hexane fraction (PZHF; 200 μg/ml). The most active PZHF inhibited QS-mediated virulence factors of P. aeruginosa PAO1 such as pyocyanin, pyoverdin, rhamnolipid production, motility, etc., significantly at sub-MICs. Similarly, PZHF showed 59 to 76% inhibition of biofilm formation of above test pathogens. The findings revealed that active fraction of P. zeylanica was effective against the QS-regulated functions and biofilms development of Gram -ve pathogenic bacteria.