Quorum Sensing Phenomenon Research Articles

Cyanobacterial Bloom Formation by Enhanced Ecological Adaptability and Competitive Advantage of Microcystis-Non-Negligible Role of Quorum Sensing.

Microcystis-dominated cyanobacterial blooms (MCBs) frequently occur in freshwaters worldwide due to massive Microcystis colony formation and severely threaten human and ecosystem health. Quorum sensing (QS) is a direct cause of Microcystis colony formation that drives MCBs outbreak by regulating Microcystis population characteristics and behaviors. Many novel findings regarding the fundamental knowledge of the Microcystis QS phenomenon and the signaling molecules have been documented. However, little effort has been devoted to comprehensively summarizing and discussing the research progress and exploration directions of QS signaling molecules-mediated QS system in Microcystis. This review summarizes the action process of N-acyl homoserine lactones (AHLs) as major signaling molecules in Microcystis and discusses the detailed roles of AHL-mediated QS system in cellular morphology, physiological adaptability, and cell aggregation for colony formation to strengthen ecological adaptability and competitive advantage of Microcystis. The research progress on QS mechanisms in Microcystis are also summarized. Compared to other QS systems, the LuxI/LuxR-type QS system is more likely to be found in Microcystis. Also, we introduce quorum quenching (QQ), a QS-blocking process in Microcystis, to emphasize its potential as QS inhibitors in MCBs control. Finally, in response to the research deficiencies and gaps in Microcystis QS, we propose several future research directions in this field. This review deepens the understanding on Microcystis QS knowledge and provide theoretical guidance in developing strategies to monitor, control, and harness MCBs.

육계농장유래 ICT-데이터의 분석을 통해 미생물의 정족수감지 (Quorum Sensing) 현상의 발견을 위한 연구

The current study obtained biometric data yielded by information and communication technology (ICT) equipment installed in the mobile phones of farmers from broiler farms and evaluated quorum sensing (QS) phenomenon (QSP), which can be considered as an emergency rescue request signal for chickens and the starting point of a disease. The results indicated that QSP was identified the most rapidly and sensitively during the analysis of digital data yielded by the ICT-equipped automatic feed feeder, followed by the water consumption data. In particular, in the data on daily feed consumption, QSP was identified to be the point where the consumption rapidly decreased by more than 100% compared with that on the previous day. It is believed that if farm owners responded to the QSP or chicken rescue signals and rapidly implemented disease prevention measures, then it would be the wisest field use of ICT data to minimize loss and damage to farms. In addition, the results of this study revealed the priority order of the introduction of ICT equipment. and the most urgent and important for farm management is daily feed consumption data by applying the scientifically based QS approach, for the first time, to our knowledge, in Korea. The results of this study uncovered the importance of installing ICT equipments.

Marine Microorganisms as Potential Source of Quorum-Sensing Inhibitory Compounds

Antibiotics are extensively utilized globally, and the rate of antibiotic resistance is increasing more rapidly than ever. Since the introduction of antibiotics, the overuse of antibiotics caused selection pressure, and almost all pathogenic bacteria have developed resistance against commonly used antibiotics, which is particularly known as antimicrobial resistance (AMR). It has proven challenging to combat and resolve the issue of microbial resistance. A growing number of microorganisms have developed different resistance mechanisms and turned into "superbugs". The identification of quorum-sensing systems has given researchers a new hope for understanding drug resistance processes. The quorum-sensing system controls a number of cellular functions, including the expression of pathogenic genes, the synthesis of toxins, and the synthesis of extracellular polysaccharides. To targeting QS systems marine bacterial samples were collected by different coastal sites of Gujarat, like Mandvi, Dwarka and Diu. A total of 52 marine isolates were obtained, out of which 16 were associated with various marine macro-organisms like sponges and algae, whereas 36 were free-living. The study has done by screening those marine isolates shown potential to inhibiting the quorum sensing molecule by co culture study against Chromobacter violaceium, followed by growth inhibition assay. The G14 and G82 isolate shows highest degradation of N-acyl homoserine lactone by AHL study. The QSI compounds were extracted using ethyl acetate extraction method. Biofilm inhibition assay with Pseudomonas aeruginosa shows potent inhibitory effect of extract. These results prove that marine microorganism have potential to inhibits quorum sensing and virulence factors regulated by Quorum Sensing phenomenon.

Attenuation of Las/Rhl quorum sensing regulated virulence and biofilm formation in Pseudomonas aeruginosa PAO1 by Artocarpesin

The emergence of multidrug resistance and increased pathogenicity in microorganisms is conferred by the presence of highly synchronized cell density dependent signalling pathway known as quorum sensing (QS). The QS hierarchy is accountable for the secretion of virulence phenotypes, biofilm formation and drug resistance. Hence, targeting the QS phenomenon could be a promising strategy to counteract the bacterial virulence and drug resistance. In the present study, artocarpesin (ACN), a 6-prenylated flavone was investigated for its capability to quench the synthesis of QS regulated virulence factors. From the results, ACN showed significant inhibition of secreted virulence phenotypes such as pyocyanin (80%), rhamnolipid (79%), protease (69%), elastase (84%), alginate (88%) and biofilm formation (88%) in opportunistic pathogen, Pseudomonas aeruginosa PAO1. Further, microscopic observation of biofilm confirmed a significant reduction in biofilm matrix when P. aeruginosa PAO1 was supplemented with ACN at its sub-MIC concentration. Quantitative gene expression studies showed the promising aspects of ACN in down regulation of several QS regulatory genes associated with production of virulence phenotypes. Upon treatment with sub-MIC of ACN, the bacterial colonization in the gut of Caenorhabditis elegans was potentially reduced and the survival rate was greatly improved. The promising QS inhibition activities were further validated through in silico studies, which put an insight into the mechanism of QS inhibition. Thus, ACN could be considered as possible drug candidate targeting chronic microbial infections.

A Holistic Approach from Systems Biology Reveals the Direct Influence of the Quorum-Sensing Phenomenon on Pseudomonas aeruginosa Metabolism to Pyoverdine Biosynthesis.

Computational modeling and simulation of biological systems have become valuable tools for understanding and predicting cellular performance and phenotype generation. This work aimed to construct, model, and dynamically simulate the virulence factor pyoverdine (PVD) biosynthesis in Pseudomonas aeruginosa through a systemic approach, considering that the metabolic pathway of PVD synthesis is regulated by the quorum-sensing (QS) phenomenon. The methodology comprised three main stages: (i) Construction, modeling, and validation of the QS gene regulatory network that controls PVD synthesis in P. aeruginosa strain PAO1; (ii) construction, curating, and modeling of the metabolic network of P. aeruginosa using the flux balance analysis (FBA) approach; (iii) integration and modeling of these two networks into an integrative model using the dynamic flux balance analysis (DFBA) approximation, followed, finally, by an in vitro validation of the integrated model for PVD synthesis in P. aeruginosa as a function of QS signaling. The QS gene network, constructed using the standard System Biology Markup Language, comprised 114 chemical species and 103 reactions and was modeled as a deterministic system following the kinetic based on mass action law. This model showed that the higher the bacterial growth, the higher the extracellular concentration of QS signal molecules, thus emulating the natural behavior of P. aeruginosa PAO1. The P. aeruginosa metabolic network model was constructed based on the iMO1056 model, the P. aeruginosa PAO1 strain genomic annotation, and the metabolic pathway of PVD synthesis. The metabolic network model included the PVD synthesis, transport, exchange reactions, and the QS signal molecules. This metabolic network model was curated and then modeled under the FBA approximation, using biomass maximization as the objective function (optimization problem, a term borrowed from the engineering field). Next, chemical reactions shared by both network models were chosen to combine them into an integrative model. To this end, the fluxes of these reactions, obtained from the QS network model, were fixed in the metabolic network model as constraints of the optimization problem using the DFBA approximation. Finally, simulations of the integrative model (CCBM1146, comprising 1123 reactions and 880 metabolites) were run using the DFBA approximation to get (i) the flux profile for each reaction, (ii) the bacterial growth profile, (iii) the biomass profile, and (iv) the concentration profiles of metabolites of interest such as glucose, PVD, and QS signal molecules. The CCBM1146 model showed that the QS phenomenon directly influences the P. aeruginosa metabolism to PVD biosynthesis as a function of the change in QS signal intensity. The CCBM1146 model made it possible to characterize and explain the complex and emergent behavior generated by the interactions between the two networks, which would have been impossible to do by studying each system's individual components or scales separately. This work is the first in silico report of an integrative model comprising the QS gene regulatory network and the metabolic network of P. aeruginosa.

Effects of exogenous AHLs on the spoilage characteristics of Pseudomonas koreensis PS1.

Some specific spoilage organisms (SSO) respond to the presence of exogenous N-acyl-homoserine lactones (AHLs) through the quorum sensing (QS) system to modulate their spoilage characteristics. To explore the effect of exogenous AHLs on the spoilage characteristics of Pseudomonas koreensis PS1 from spoiled chilled pork, four kinds of AHLs were added to the liquid medium to analyze their effect on the cell growth and spoilage characteristics of P. koreensis PS1, and N-hexanoyl-l-homoserine lactone (C6-HSL) was added to evaluate its effect on spoilage characteristics of P. koreensis PS1 inoculated in fresh chilled pork. The results showed that the addition of low concentrations of C6-HSL (10µmol/L) to the liquid medium could remarkably promote the protease activity, lipase activity, and biofilm formation of P. koreensis PS1 (p < 0.05), and more than 30µmol/L C6-HSL could significantly increase the cell density (p < 0.05). Furthermore, the addition of 10µmol/L C6-HSL into fresh chilled pork could increase the lipase and protease activities of P. koreensis PS1. The enzyme activity accelerated the decomposition of total protein, total fat, and total sugar, and led to an increase in putrescine, tyramine, cadaverine, and total volatile basic nitrogen (TVB-N) content in chilled pork during the storage at 4°C. PRACTICAL APPLICATION: The infestation of chilled pork with SSO may be a challenge for the meat industry. In this study, exogenous AHLs were found to have a positive effect on the spoilage of chilled pork. The elimination of the QS phenomenon of bacteria should be considered when looking for ways to prolong the preservation of chilled pork.

Synchronisation of glycolytic activity in yeast cells.

Glycolysis is the central metabolic pathway of almost every cell and organism. Under appropriate conditions, glycolytic oscillations may occur in individual cells as well as in entire cell populations or tissues. In many biological systems, glycolytic oscillations drive coherent oscillations of other metabolites, for instance in cardiomyocytes near anorexia, or in pancreas where they lead to a pulsatile release of insulin. Oscillations at the population or tissue level require the cells to synchronize their metabolism. We review the progress achieved instudying a model organism for glycolytic oscillations, namely yeast. Oscillations may occur on the level of individual cells as well as on the level of the cell population. In yeast, the cell-to-cell interaction is realized by diffusion-mediated intercellular communication via a messenger molecule. The present mini-review focuses on the synchronisation of glycolytic oscillations in yeast. Synchronisation is a quorum-sensing phenomenon because the collective oscillatory behaviour of a yeast cell population ceases when the cell density falls below a threshold. We review the question, under which conditions individual cells in a sparse population continue or cease to oscillate. Furthermore, we provide an overview of the pathway leading to the onset of synchronized oscillations. We also address the effects of spatial inhomogeneities (e.g., the formation of spatial clusters) on the collective dynamics, and also review the emergence of travelling waves of glycolytic activity. Finally, we briefly review the approaches used in numerical modelling of synchronized cell populations.

ACYL-HOMOSERINE LACTONES FOR CROP PRODUCTION AND STRESS TOLERANCE OF AGRICULTURAL PLANTS (review)

Acyl homoserine lactones (AHL) are a class of mediator molecules coordinating cell activity in the gram-negative bacteria population. AHLs synchronize individual genomes due to which bacterial populations function as a multicellular organism. AHLs provide a remote signaling between bacteria colonizing the phytosphere that enables the bacterial population to respond to external influences and establish symbiotic or antagonistic relationships with the host plant (A.R. Stacy et al., 2018; A. Shrestha et al., 2020). Autoreception of quantitative parameters of the bacterial population is called quorum sensing (QS) (R.G. Abisado et al., 2018). QS systems form autoinducer signaling molecules that easily penetrate from cells into the environment and back into the cell (M.B. Miller et al., 2001; B. Bassler, 2002). QS systems play a key role in the regulation of metabolic and physiological processes in a bacterial cell (M. Frederix et al., 2011; M. Whiteley et al., 2017). Bacterial signaling is perceived by eukaryotes, which form a symbiosis with microbial communities (A. Schenk et al., 2015; L.M. Babenko et al., 2016, 2017). Plant growth and development, nutrients assimilation, and stress resistance are largely determined by the pattern of this interaction (H.P. Bais et al., 2006; R. Ortíz-Castro et al., 2009; S. Basu et al., 2017). In the plant, bacterial signaling is controlled by the quorum quenching (QQ) system (N. Calatrava-Morales et al., 2018), whose mechanism of action is to suppress AHL synthesis by plant metabolites, compete with AHL for binding to receptor proteins, and repression of QS-controlled genes (H. Zhu et al., 2008; R. Sarkar et al., 2015). However, to date, the molecular mechanisms by which plants respond to bacterial signaling are not fully understood. Individual metabolites of AHL signaling have been characterized, but their role in the chemical interaction of partners in most cases requires further study. It has been shown that the QS phenomenon and its participants are involved in the regulation of prokaryotic-eukaryotic interactions, including the formation of biofilms, the synthesis of phytohormones, the transfer of plasmids, the production of virulence factors, bioluminescence, sporulation, and the formation of nodules (L.M. Babenko et al., 2017). Differences in the structure of molecules ensure that bacteria recognize their own AHL and separate foreign ones. The transfer of AHL from a bacterium to a host plant is carried out by means of membrane vesicles (M. Toyofuku, 2019). In recent years, there has been an active study of genetics, genomics, biochemistry, and signaling diversity of QS molecules. The regulation of the functions of the rhizosphere, the most dynamic site of interaction between the plant and the associated microflora with the participation of AHL, is of particular importance in the development of new biotechnological approaches aimed at increasing the yield and stress resistance of agricultural crops. One of the effective technologies for increasing resistance to biotic and abiotic stresses is pre-sowing treatment (priming) of seeds (A. Shrestha et al., 2020). Both direct (on plants) and indirect (on rhizosphere microflora) effects of AHL priming was established (O.V. Moshynets et al., 2019). AHL induce an increase of growth, of photosynthetic pigments content, as well as cause changes in the ratio of phytohormones in organs and tissues, affect the formation of defense mechanisms, which increases the productivity of agricultural crops (A. Schikora, S.T. Schenk, 2016; A. Shrestha et al., 2020). AHL meet the requirements of intensive organic farming, they are considered as promising ecological phytostimulants and phytomodulators capable of safely increasing the quantity and quality of agricultural products.

АЦИЛГОМОСЕРИНЛАКТОНЫ КАК РЕГУЛЯТОРЫ УРОЖАЙНОСТИ И СТРЕССОУСТОЙЧИВОСТИ СЕЛЬСКОХОЗЯЙСТВЕННЫХ КУЛЬТУР (обзор)

Acyl homoserine lactones (AHL) are a class of mediator molecules coordinating cell activity in the gram-negative bacteria population. AHLs synchronize individual genomes due to which bacterial populations function as a multicellular organism. AHLs provide a remote signaling between bacteria colonizing the phytosphere that enables the bacterial population to respond to external influences and establish symbiotic or antagonistic relationships with the host plant (A.R. Stacy et al., 2018; A. Shrestha et al., 2020). Autoreception of quantitative parameters of the bacterial population is called quorum sensing (QS) (R.G. Abisado et al., 2018). QS systems form autoinducer signaling molecules that easily penetrate from cells into the environment and back into the cell (M.B. Miller et al., 2001; B. Bassler, 2002). QS systems play a key role in the regulation of metabolic and physiological processes in a bacterial cell (M. Frederix et al., 2011; M. Whiteley et al., 2017). Bacterial signaling is perceived by eukaryotes, which form a symbiosis with microbial communities (A. Schenk et al., 2015; L.M. Babenko et al., 2016, 2017). Plant growth and development, nutrients assimilation, and stress resistance are largely determined by the pattern of this interaction (H.P. Bais et al., 2006; R. Ortíz-Castro et al., 2009; S. Basu et al., 2017). In the plant, bacterial signaling is controlled by the quorum quenching (QQ) system (N. Calatrava-Morales et al., 2018), whose mechanism of action is to suppress AHL synthesis by plant metabolites, compete with AHL for binding to receptor proteins, and repression of QS-controlled genes (H. Zhu et al., 2008; R. Sarkar et al., 2015). However, to date, the molecular mechanisms by which plants respond to bacterial signaling are not fully understood. Individual metabolites of AHL signaling have been characterized, but their role in the chemical interaction of partners in most cases requires further study. It has been shown that the QS phenomenon and its participants are involved in the regulation of prokaryotic-eukaryotic interactions, including the formation of biofilms, the synthesis of phytohormones, the transfer of plasmids, the production of virulence factors, bioluminescence, sporulation, and the formation of nodules (L.M. Babenko et al., 2017). Differences in the structure of molecules ensure that bacteria recognize their own AHL and separate foreign ones. The transfer of AHL from a bacterium to a host plant is carried out by means of membrane vesicles (M. Toyofuku, 2019). In recent years, there has been an active study of genetics, genomics, biochemistry, and signaling diversity of QS molecules. The regulation of the functions of the rhizosphere, the most dynamic site of interaction between the plant and the associated microflora with the participation of AHL, is of particular importance in the development of new biotechnological approaches aimed at increasing the yield and stress resistance of agricultural crops. One of the effective technologies for increasing resistance to biotic and abiotic stresses is pre-sowing treatment (priming) of seeds (A. Shrestha et al., 2020). Both direct (on plants) and indirect (on rhizosphere microflora) effects of AHL priming was established (O.V. Moshynets et al., 2019). AHL induce an increase of growth, of photosynthetic pigments content, as well as cause changes in the ratio of phytohormones in organs and tissues, affect the formation of defense mechanisms, which increases the productivity of agricultural crops (A. Schikora, S.T. Schenk, 2016; A. Shrestha et al., 2020). AHL meet the requirements of intensive organic farming, they are considered as promising ecological phytostimulants and phytomodulators capable of safely increasing the quantity and quality of agricultural products.

Study of the Regulatory Role of N-Acyl Homoserine Lactones Mediated Quorum Sensing in the Biological Activity of Burkholderia gladioli pv. agaricicola Causing Soft Rot of Agaricus spp.

Many Burkholderia spp. produce in vitro secondary metabolites with relevant biological activities and potential practical applications. Burkholderia gladioli pv. agaricicola (Bga) possess promising biological activities regulated by N-Acyl homoserine lactones (N.AHLs) based quorum sensing (QS) mechanism. In the current study, N.AHLs-deficient (ICMP11096glad-I) and N.AHLs-complemented (ICMP11096glad-IR) mutants were constructed in which the gene coding for AHL synthase was inactivated by allelic exchange in glad I mutant strain. The aims of this research were to (i) assess the antagonistic activity of the wild type (WT) and the glad-I mutant of Bga against Bacillus megaterium (G+ve) and Escherichia coli (G−ve), (ii) screen their hydrolytic enzymes and hemolytic substances, (iii) monitor the pathogenic effect against Agaricus bisporus, and finally (iv) analyze the bioactive secondary metabolites produced by WT and mutant strain using high performance liquid chromatography (HPLC). Results showed that N.AHLs-deficient mutant exhibited high reduction of antagonistic activity against the tested microorganisms and notable reduction of chitinolytic, proteolytic and glucanolytic activities and complete absence of hemolytic activity, and the glad-IR complemented mutant was able to regain the major part of these activities. Furthermore, N.AHLs-deficient mutant strain was unable to degrade flesh cubes pseudo-tissues of A. bisporus. On the other hand, the virulence effect of complemented mutant was like to the parental WT strain. HPLC analysis revealed that some of the single components produced by WT strain were absent in N.AHLs-deficient mutant and others were highly reduced. The out-findings of the current research gave a spot into the regulatory role of N.AHLs and QS phenomenon in the biological activity of Bga bacterium.

Elucidation of quorum sensing components and their role in regulation of symbiotically important traits in Ensifer nodulating pigeon pea

Quorum sensing (QS) in rhizobia regulates diverse processes determining the success and efficiency of association with the legume host. Despite the notable importance of QS as well as the well-known underlying variability in the genomic and metabolic components thereof, its study in rhizobia is largely restricted to few laboratory strains. In this work, QS phenomenon in the rhizobia nodulating pigeon pea– one of the most important legume crops of the global-south, is characterized. Using 16S rRNA and recombinaseA sequencing analysis, the selected QS-positive and host-beneficial isolates were identified to be taxonomically affiliated to the genus Ensifer. Their QS components, including homologues of QS genes, and the repertoire of N-acyl homoserine lactone (AHL) autoinducers were identified. Sequences of the QS homologues showed significant variabilities ranging from 10 to >20% with the known Ensifer sequences. Autoinducer profiling using LC–MS/MS revealed the production of long and short chain AHLs variably by the isolates, including 3-oxo-C12-homoserine lactone (3-O-C12-HSL) and 3-OH-C16-HSL as their first report in Rhizobiaceae. Motility and attachment– two of the most crucial traits for effective establishment on host roots were discovered to be QS dependent in in vitro analysis and the same was confirmed using expression analysis of their regulatory genes using qRT-PCR; both revealing a QS mediated repression of motility and promotion of attachment. This study highlights that Ensifer nodulating pigeon pea, although with significant variance in the anatomy of their QS components, regulate symbiotically crucial cell-processes via QS in a scheme that is conserved in multiple genera.

Dissolved oxygen-mediated enrichment of quorum-sensing phenomenon in the bacterial community to combat oxidative stress

Microbial community with their plasticity follows a course of changes that allow adaptation and survival in a particular habitat. In this study perturbations in microbial flora dwelling in two reactors with phenol as a carbon source under the limiting nitrogen and phosphorus conditions were monitored for 3months with alterations of dissolved oxygen (DO). With the time, the shift in diversity and abundance of bacteria were observed with simultaneous increase in biofilm-forming bacteria like Pseudomonas, Escherichia, etc. Functional level screening revealed that the abundance of core metabolic genes were not much altered, however, the regulated level of increase in quorum sensing genes (acyl-homoserine lactone), biofilm-forming genes, catalase and ferroxidase enzymes at high DO suggest the survival mechanism of the community. This study sheds light on survival route followed by the bacterial community with abiotic stress, such as an increase in DO.

Impact of curcumin liposomes with anti-quorum sensing properties against foodborne pathogens Aeromonas hydrophila and Serratia grimesii

Quorum sensing (QS) is a signal sensing system by which bacteria monitor the density of their population, thus, targeting to QS system may be an alternative approach to control diverse cellular processes including the microbial contamination and the virulence of human and plant pathogens as bacteria have been evolving resistance to antibiotics. In this study, curcumin liposomes were prepared by film dispersion method to increase its bioavailability against QS systems of food-borne epathogenic bacteria, i.e. Aeromonas hydrophila and Serratia grimesii. And their physicochemical properties were measured including particle size, zeta-potential entrapment rate as well as drug-loading rate. Meanwhile, the effects of curcumin liposomes on QS phenomenon of food-borne pathogens including biofilm formation, extracellular protease, swimming motility et al. were determined. Results showed that the average diameter of curcumin liposomes was (207 ± 8.2) nm and the entrapment rate and drug-loading rate were 82.71% and 23.33%. The zeta-potential of curcumin liposomes were (−37 ± 1.56) mv. Curcumin liposomes showed uniform structures by scanning electron microscopy (SEM). The curcumin liposomes could significantly inhibit QS systems of the two pathogens and the biological availability of curcumin has been improved.

Molecular basis of quorum sensing signal-response systems in bacteria

Bacteria use quorum sensing (QS) to conduct gene expression programmes connected with collective behaviors. QS indicates on the capacity of bacteria to monitor their population density and regulate gene expression. QS activates from tens to hundreds of genes that underlie different biological processes. The QS-regulated processes organize horizontal gene transfer, the formation of biofilms, multicellular behaviors, microbe–host and microbe–microbe relations. The QS signaling requires the production, release, detection, exchange and perception of bacterial compounds, known as autoinducers or QS signals. Recently, new autoinducers have been discovered in bacteria and it has been shown how these molecules are recognized by the respective receptors. Autoinducers belong to three major classes: acyl-homoserine lactones (AHLs) used by Gram-negative bacteria, specific oligopeptides used by Gram-positive bacteria and universal autoinducers. The aim of this paper is to provide an overview of molecular basis of the QS phenomenon, characterization of intra- and interspecies QS signaling molecules and biological processes regulated by these molecules.

Protein-protein interaction and molecular dynamics analysis for identification of novel inhibitors in Burkholderia cepacia GG4

The lack of complete treatments and appearance of multiple drug-resistance strains of Burkholderia cepacia complex (Bcc) are causing an increased risk of lung infections in cystic fibrosis patients. Bcc infection is a big risk to human health and demands an urgent need to identify new therapeutics against these bacteria. Network biology has emerged as one of the prospective hope in identifying novel drug targets and hits. We have applied protein–protein interaction methodology to identify new drug-target candidates (orthologs) in Burkhloderia cepacia GG4, which is an important strain for studying the quorum-sensing phenomena. An evolutionary based ortholog mapping approach has been applied for generating the large scale protein–protein interactions in B. Cepacia. As a case study, one of the identified drug targets; GEM_3202, a NH (3)-dependent NAD synthetase protein has been studied and the potential ligand molecules were screened using the ZINC database. The three dimensional structure (NH (3)-dependent NAD synthetase protein) has been predicted from MODELLERv9.11 tool using multiple PDB templates such as 3DPI, 2PZ8 and 1NSY with sequence identity of 76%, 50% and 50% respectively. The structure has been validated with Ramachandaran plot having 100% residues of NadE in allowed region and overall quality factor of 81.75 using ERRAT tool. High throughput screening and Vina resulted in two potential hits against NadE such as ZINC83103551 and ZINC38008121. These molecules showed lowest binding energy of −5.7kcalmol−1 and high stability in the binding pockets during molecular dynamics simulation analysis. The similar approach for target identification could be applied for clinical strains of other pathogenic microbes.

Intra-layer synchronization in multiplex networks

We study synchronization of N oscillators indirectly coupled through a medium which is inhomogeneous and has its own dynamics. The system is formalized in terms of a multilayer network, where the top layer is made of disconnected oscillators and the bottom one, modeling the medium, consists of oscillators coupled according to a given topology. The different dynamics of the medium and the top layer is accounted for by including a frequency mismatch between them. We show a novel regime of synchronization as intra-layer coherence does not necessarily require inter-layer coherence. This regime appears under mild conditions on the bottom layer: arbitrary topologies may be considered, provided that they support synchronization of the oscillators of the medium. The existence of a density-dependent threshold as in quorum-sensing phenomena is also demonstrated.

Synthesis and Bio-Film Inhibition Activity of Betulinan C and its Analogs

In present study, we report synthesis of Betulinan C and its analogs and explore its biological application as an agent inhibiting the biofilm formation in Pseudomonas aeruginosa O1. P. aeruginosa biofilm is prominently inhibited 80–83% by compounds 2a and 1b at 25 μg/mL. While other analogs show a mixed response. Biofilm inhibition is further confirmed by Scanning Electron Microscopy. The present study is important as Betulinan C has been produced by a fungus of order Chaetothyriales and there are no chemical methods yet reported for its synthesis. The inhibition of biofilm is due to inhibition of quorum sensing (QS) phenomenon. Contrary to the traditional bioactive molecules, QS phenomenon is not essential for the survival of cells, and therefore, present compounds will not create a selection pressure of antibiotics resistance in cells on which they act.

Microbial metabolism of quorum-sensing molecules acyl-homoserine lactones, γ-heptalactone and other lactones

The cell-to-cell communication of microorganisms is known to be via exertion of certain chemical compounds (signal molecules) and is referred to as quorum sensing (QS). QS phenomenon is widespread in microbial communities. Several Gram-positive and Gram-negative bacteria and fungi use lactone-containing compounds (e.g. acyl-homoserine lactones (AHLs), γ-heptalactone, butyrolactone-I) as signalling molecules. The ability of microorganisms to metabolise these compounds and the mechanisms they employ for this purpose are not clearly understood. Many studies, however, have focused on identifying AHL and other lactone-degrading enzymes produced by bacteria and fungi. Various strains that are able to utilise these signalling molecules as carbon and energy sources have also been isolated. In addition, several reports have provided evidence on the involvement of lactones and lactone-degrading enzymes in numerous biological functions. These studies, although focused on processes other than metabolism of lactone signalling molecules, still provide insights into further understanding of the mechanisms employed by various microorganisms to metabolise the QS compounds. In this review, we consider conceivable microbial strategies to metabolise AHL and other lactone-containing signalling molecules such as γ-heptalactones.

Pathway engineering via quorum sensing and sRNA riboregulators—Interconnected networks and controllers

The advent of genetic engineering has elevated our level of comprehension of cellular processes and functions. A natural progression of these findings is determining not only how these processes function within individual cells but also within a community. Bacterial cells monitor the conditions and microorganisms in their vicinity by producing, releasing and sensing chemical-signaling molecules. When a specific cell-density threshold is reached, a quorum is perceived, gene expression profiles are altered and the community orchestrates activities that are more effective en masse. This communication mechanism, in the language of autoinducers (AI), is referred to as quorum sensing (QS). It has become increasingly evident that while scientists attempt to decipher the intricacies of cellular communication and quorum sensing networks, we must remain conscious of the broader context of how a cell may identify itself in the environment and how this also impacts QS. Importantly, these phenomena span time and length scales by several orders in magnitude. Though the revelation of small RNAs, as both sensing and regulatory elements participating in the quorum sensing cascade, has connected new pieces of the puzzle, it has also added a new tier of uncertainty. The complexity of quorum sensing networks makes resolution of its diverse mechanisms difficult. The ability to design simpler networks with defined, more predictable or even “modular” elements will help elucidate these actions. Because it embraces innovative concepts of biological design accommodating the many length and time scales at play, synthetic biology serves as one of the most promising platforms for describing QS phenomena as well as enabling novel implementation strategies for biotechnological application.

Candida and invasive candidiasis: back to basics

The ubiquitous Candida spp. is an opportunistic fungal pathogen which, despite treatment with antifungal drugs, can cause fatal bloodstream infections (BSIs) in immunocompromised and immunodeficient persons. Thus far, several major C. albicans virulence factors have been relatively well studied, including morphology switching and secreted degradative enzymes. However, the exact mechanism of Candida pathogenesis and the host response to invasion are still not well elucidated. The relatively recent discovery of the quorum-sensing molecule farnesol and the existence of quorum sensing as a basic regulatory phenomenon of the C. albicans population behavior has revolutionized Candida research. Through population density regulation, the quorum-sensing mechanism also controls the cellular morphology of a C. albicans population in response to environmental factors, thereby, effectively placing morphology switching downstream of quorum sensing. Thus, the quorum-sensing phenomenon has been hailed as the 'missing piece' of the pathogenicity puzzle. Here, we review what is known about Candida spp. as the etiological agents of invasive candidiasis and address our current understanding of the quorum-sensing phenomenon in relation to virulence in the host.