Lactone Molecules Research Articles

Effect of Matricaria aurea Essential Oils on Biofilm Development, Virulence Factors and Quorum Sensing-Dependent Genes of Pseudomonas aeruginosa.

The emergence of drug-resistant microorganisms presents a substantial global public health threat. The increase in pathogens resistant to commonly prescribed antibiotics underscores the urgent requirement to explore alternative treatment strategies. This study adopts a novel approach by harnessing natural resources, specifically essential oils (EO), to combat bacterial pathogenicity. The primary aim of this research was to analyze the chemical composition of the aerial part of the Matricaria aurea (M. aureas) EO and evaluate its potential for inhibiting quorum sensing (QS) and disrupting biofilm formation in Pseudomonas aeruginosa (P. aeruginosa). The gas chromatography-mass spectrometry (GCMS) analysis unveiled that α-bisabolol oxide A constituted the predominant portion, comprising 64.8% of the total, with β-bisabolene at 6.3% and α-farnesene at 4.8% following closely behind. The antibiofilm efficacy was observed at concentrations of 0.3, 0.15, and 0.08 mg/mL, demonstrating negligible effects on cell viability. Furthermore, the EO from M. aurea effectively inhibited the formation of P. aeruginosa biofilms by diminishing aggregation, hydrophobicity, and swarming motility. Significantly, the EO treatment resulted in a conspicuous decrease in the production of pyocyanin, rhamnolipid, and extracellular polymeric substances (EPS), along with a reduction in the enzymatic activity of protease and chitinase. The EO effectively hindered QS by disrupting QS mechanisms, resulting in a marked decline in the secretion of N-Acyl homoserine lactone (AHL) molecules and the expression of phazA1 and aprA genes. This investigation offers compelling evidence supporting the potential of M. aurea EO as a promising therapeutic candidate for addressing infectious diseases induced by biofilm formation.

Insights into additional lactone-based signaling circuits in Streptomyces: existence of acyl-homoserine lactones and LuxI/LuxR homologs in six Streptomyces species.

Acyl-homoserine lactones (AHLs), mediating pivotal physiological activities through quorum sensing (QS), have conventionally been considered limited to Gram-negative bacteria. However, few reports on the existence of AHLs in Gram-positive bacteria have questioned this conception. Streptomyces, as Gram-positive bacteria already utilizing a lactone-based QS molecule (i.e., gamma-butyrolactones), are yet to be explored for producing AHLs, considering their metabolic capacity and physiological distinction. In this regard, our study examined the potential production of AHLs within Streptomyces by deploying HPLC-MS/MS methods, which resulted in the discovery of multiple AHL productions by S. griseus, S. lavendulae FRI-5, S. clavuligerus, S. nodosus, S. lividans, and S. coelicolor A3(2). Each of these Streptomyces species possesses a combination of AHLs of different size ranges, possibly due to their distinct properties and regulatory roles. In light of additional lactone molecules, we further confirm that AHL- and GBL-synthases (i.e., LuxI and AfsA enzyme families, respectively) and their receptors (i.e., LuxR and ArpA) are evolutionarily distinct. To this end, we searched for the components of the AHL signaling circuit, i.e., AHL synthases and receptors, in the Streptomyces genus, and we have identified multiple potential LuxI and LuxR homologs in all 2,336 Streptomyces species included in this study. The 6 Streptomyces of interest in this study also had at least 4 LuxI homologs and 97 LuxR homologs. In conclusion, AHLs and associated gene regulatory systems could be more widespread within the prokaryotic realm than previously believed, potentially contributing to the control of secondary metabolites (e.g., antibiotics) and their complex life cycle, which leads to substantial industrial and clinical applications.

All-atom molecular dynamics simulations showing the dynamics of small organic molecules in water-solvated polyelectrolyte brush layers.

Polyelectrolyte brushes can introduce functionality to surfaces and because of this, these brushes have been studied extensively. In many applications, these brushes are used in solutions that contain a variety of molecules. While the interaction between polyelectrolyte brushes and molecules has been studied via coarse-grained simulations and experiments, such interaction has not been studied in molecular detail. An understanding of interactions in such molecular detail may prove crucial in the design of future brush coatings that can enable desired adsorption of different organic and biological molecules. Therefore, we present a first all-atom molecular dynamics simulations study of poly(sodium acrylate) brushes in contact with a small organic molecule, γ-butyrolactone. Within this molecular framework, we study the interaction of this lactone molecule with the brush layer and study the ensuing absorption and dynamics of the lactone inside the brush layer. The lactone is found to prefer to remain in the bulk solution; however, when absorbed, lactone molecules are found to have significantly reduced mobilities as compared to that in the bulk solution and are able to massively influence the properties of the brush-entrapped water molecules. These findings provide unprecedented details about the absorption-driven changes to molecular structure and dynamics of the lactone molecules and the water molecules inside the brush layer and can only be uncovered by our all-atom MD simulations. Such explicit and atomistically-resolved information, taking into account the specific chemical nature of the interacting systems, is rare in the context of designing polymer and PE brush-based coatings. Thus, we anticipate that our findings will be crucial in the design of future brush coatings aimed at providing adsorption platforms for different organic and biomolecules.

Characterization of the defense properties of healthy and diseased coral mucus

The surface mucus layer of corals aids in feeding, silt removal, and defense against pathogens. However, first line of defense of secreted mucus of corals against tissue damage generated through pathogen or environmental factors is poorly understood. Hence, we used various methods such as a well diffusion assay and tests for quorum quenching, free radical scavenging, antioxidant enzyme expression and phenoloxidase (PO) activity to determine the mucus defense properties using mucus of healthy and diseased Porites sp. and Acropora sp. Interestingly the coral mucus showed antimicrobial activity against coral pathogens such as bacteria and protozoan ciliates. Inhibition of the N-Acyl homoserine lactone (AHL) molecule suggests quorum quenching. Free radical scavenging of mucus was screened using hydrogen peroxide, hydroxyl radical, and 2, 2-diphenyl-1-picrylhydrazyl (DPPH) methods, which was found significantly more in diseased corals (p < 0.05). Antioxidant enzymes superoxide dismutase (SOD), catalase, and peroxidase activity were observed in both the diseased and healthy coral mucus. The presence of serine and metalloproteases was also detected in coral mucus. Further, phenoloxidase (PO) activity was highest in diseased coral mucus affected by pink line syndrome and white patch Acropora sp. disease than the healthy coral mucus. Thus, the present study of antimicrobial properties, antioxidant enzymes, and quorum quenching properties in coral mucus may aid in understanding the corals defense and survival against pathogens and any abiotic stress.

Stepwise co-fermented traditional Chinese medicine byproducts improve antioxidant and anti-inflammatory effects in a piglet model.

Lianhua Qingwen capsule is a traditional Chinese medicine (TCM) formula having antiviral and anti-inflammatory activities. During capsule production, a large amount of byproducts will be yielded and disposed of as waste by burying. Resourceful utilization of these kinds of TCM byproducts as feed additives through stage-based co-fermentation using enzyme and probiotics could reduce environmental stress and resource shortage. The in vitro characterization and the supplementary effects of fermented TCM byproducts (FTCM) for weaned piglets (initial body weight: 7.23 ± 0.33 kg; dose: basal diet + 300 mg kg-1 FTCM) were investigated. Higher reducing sugar content, total flavonoid content, flavonoid compounds (e.g. tectoridin, tricetin, flavone, apigenin, naringenin) and total antioxidant activity were determined in the FTCM compared to spontaneously fermented and unfermented materials. Supplementation of the FTCM to piglets did not significantly affect the feed intake, body weight gain and feed/gain ratio, but significantly decreased a proinflammatory cytokine, IL-8, and increased intestinal total antioxidant activity (TAC) and superoxide dismutase (SOD) activity. Moreover, FTCM supplementation increased α-diversity of the colonic microbiota accompanied with increased abundance of Prevotella genus and Treponema berlinense species. Correlation analysis indicates that T. berlinense is responsible for the decreased IL-8 level and enhanced intestinal TAC and SOD activities which might be mediated by a homoserine lactone molecule (3-oxo-C14). Overall, the stepwise co-fermentation enriched bioactive compounds within the TCM byproducts and their dietary supplementation did not generate any side effect on growth performance but displayed beneficial effects on enrichment of potential probiotic T. berlinense and relevant functions. © 2023 Society of Chemical Industry.

Identification and Characterization of Sesquiterpene Lactones as Potential Falcipain-2 Inhibitors

Drug resistance affects the most effective anti-malarial medications, hence finding new, unique bioactive compounds with strong anti-malarial activity is extremely desirable. Falcipain-2 (2GHU) is a protease of plasmodium falciparum and considered as an important target to design antimalarial drugs. Objective: To identify potential novel falcipan-2 inhibitor for effect treatment of malaria. Methods: Molecular docking analysis was performed by using different bioinformatic tools to check the interaction between the Alantolactone and Brevilin A and falcipain-2 (2GHU). Results: Alantolactone and Brevilin A show a strong affinity to bind with 2GHU with binding energy values -7.2kcal/mol and -8.1kcal/mol respectively. Moreover, results of ADMET and cytotoxicity analysis showed that both investigated compounds strongly followed the Lipinski rule of five for drug-likeness and are quite safe to be used as an antimalarial drug. Conclusions: Both of the studied sesquiterpene lactones may inhibit falcipain-2, according to the results of our molecular docking study, but Brevilin A is predicted to be the most effective inhibitor because it forms strong hydrogen bonds with the protein's amino acid residues and has lower values for binding energy and inhibition constant. Therefore, new anti-malarial medications can be created from these two bioactive sesquiterpene lactone molecules to overcome the resistance of plasmodium falciparum against already clinically approved drugs.

Molecular Mechanisms and Applications of N-Acyl Homoserine Lactone-Mediated Quorum Sensing in Bacteria.

Microbial biodiversity includes biotic and abiotic components that support all life forms by adapting to environmental conditions. Climate change, pollution, human activity, and natural calamities affect microbial biodiversity. Microbes have diverse growth conditions, physiology, and metabolism. Bacteria use signaling systems such as quorum sensing (QS) to regulate cellular interactions via small chemical signaling molecules which also help with adaptation under undesirable survival conditions. Proteobacteria use acyl-homoserine lactone (AHL) molecules as autoinducers to sense population density and modulate gene expression. The LuxI-type enzymes synthesize AHL molecules, while the LuxR-type proteins (AHL transcriptional regulators) bind to AHLs to regulate QS-dependent gene expression. Diverse AHLs have been identified, and the diversity extends to AHL synthases and AHL receptors. This review comprehensively explains the molecular diversity of AHL signaling components of Pseudomonas aeruginosa, Chromobacterium violaceum, Agrobacterium tumefaciens, and Escherichia coli. The regulatory mechanism of AHL signaling is also highlighted in this review, which adds to the current understanding of AHL signaling in Gram-negative bacteria. We summarize molecular diversity among well-studied QS systems and recent advances in the role of QS proteins in bacterial cellular signaling pathways. This review describes AHL-dependent QS details in bacteria that can be employed to understand their features, improve environmental adaptation, and develop broad biomolecule-based biotechnological applications.

ASSESSMENT OF QUORUM QUENCHING ACTIVITY OF SERRATIA SPP. ISOLATED FROM PLANT RHIZOSPHERE AGAINST QUORUM SENSING CONTROLLED BIOFILM-FORMING PATHOGENS

Quorum quenching is the process of blocking quorum sensing activity that can be used as an effective way to control quorum sensing dependent virulence in pathogens. Quorum quenching mechanisms prevent the development of antibiotic resistance in biofilm-forming microorganisms. Rhizospheric bacteria shows great diversity along with complex intra species interactions. Within this diversified environment many bacterial species with quorum sensing and quorum quenching ability are found in close vicinity. In this study rhizospheric soil of different plants was used to screen potential quorum quenchers. The rhizospheric bacterial isolates were tested for their ability to degrade/inactivate N-hexanoyl-l-homoserine lactone (C6HSL) molecules. Pigment inhibition bioassays were performed using Chromobacterium violaceum CV026 and C. violaceum 2656 to screen bacterial isolates possessing quorum quenching activity. The biofilm formation inhibition by six screened isolates was studied against different human pathogens such as Vibrio parahaemolyticus MTCC451, V. cholerae MTCC3906 and Pseudomonas aeruginosa PA01. Results revealed that biofilms were efficiently inhibited. Significant biofilm inhibition was revealed by two isolates and identified as S. marcescens subsp. sakuensis KRED, and S. nematodiphila using 16S rRNA gene sequencing technique. The partial purification of C6HSL inactivating quorum quenching molecule resulted in maximum pigment inhibition of C. violaceum 2656 at 80% saturation of ammonium sulphate. These findings revealed that S. marcescens subsp. sakuensis KRED and S. nematodiphila are found to be potential candidates to control biofilms in bacterial human pathogens.

Detection of Quorum Sensing N-Acyl-Homoserine Lactone Molecules Produced by Different Resistant Klebsiella pneumoniae Isolates Recovered from Poultry and Different Environmental Niches.

This study aimed to detect and identify the N-acyl-homoserine lactones molecules (AHLs) produced by different resistant Klebsiella pneumoniae isolates recovered from poultry and environmental samples using a modified validated high-performance liquid chromatography method. A total of 56 K. pneumoniae isolates were recovered, investigated for their antibiotic susceptibility, and screened for AHLs production using the Agrobacterium tumefaciens NTL4 biosensor system and a validated high-performance liquid chromatography method. The results revealed the detection of different short- and long-chain AHLs molecules among 39 K. pneumoniae isolates recovered from poultry and environmental samples. All environmental isolates produced nine peaks with retention times for C4-HSL, C6-HSL, C12-HSL, C8-HSL, C14-HSL, C8-oxo-HSL, C10-HSL, C6-oxo-HSL, and C7-HSL. The most quantifiable AHL signal molecules in poultry isolates were C4-HSL, C6-HSL, and C12-HSL. No statistical correlation between the AHL-producing ability of K. pneumoniae isolates and antibiotic resistance was reported. To the best of our knowledge, this study provides the first detailed report on the detection and identification of AHLs in K. pneumoniae isolates recovered from poultry and environmental samples. Furthermore, it provides a new insight available tool other than LC-MS/MS for detection and identification of AHL molecules.

Temperature and immigration effects on quorum sensing in the biofilms of anaerobic membrane bioreactors

Quorum sensing (QS), a microbial communication mechanism modulated by acyl homoserine lactone (AHL) molecules impacts biofilm formation in bioreactors. This study investigated the effects of temperature and immigration on AHL levels and biofouling in anaerobic membrane bioreactors. The hypothesis was that the immigrant microbial community would increase the AHL-mediated QS, thus stimulating biofouling and that low temperatures would exacerbate this. We observed that presence of immigrants, especially when exposed to low temperatures indeed increased AHL concentrations and fouling in the biofilms on the membranes. At low temperature, the concentrations of the main AHLs observed, N-dodecanoyl-L-homoserine lactone and N-decanoyl-L-homoserine lactone, were significantly higher in the biofilms than in the sludge and correlated significantly with the abundance of immigrant bacteria. Apparently low temperature, immigration and denser community structure in the biofilm stressed the communities, triggering AHL production and excretion. These insights into the social behaviour of reactor communities responding to low temperature and influx of immigrants have implications for biofouling control in bioreactors.

N-acyl homoserine lactone molecules assisted quorum sensing: effects consequences and monitoring of bacteria talking in real life.

Bacteria utilize small signal molecules to monitor population densities. Bacteria arrange gene regulation in a method called Quorum Sensing (QS). The most widespread signalling molecules are N-Acyl Homoserine Lactones (AHLs/HSLs) for Gram-negative bacteria communities. QS plays significant role in the organizing of the bacterial gene that adapts to harsh environmental conditions for bacteria. It is involved in the arrangement of duties, such as biofilm formation occurrence, virulence activity of bacteria, production of antibiotics, plasmid conjugal transfer incident, pigmentation phenomenon and production of exopolysaccharide (EPS). QS obviously impacts on human health, agriculture and environment. AHL-related QS researches have been extensively studied and understood in depth for cell to cell intercommunication channel in Gram-negative bacteria. It is understood that AHL-based QS research has been extensively studied for cell-to-cell communication in Gram-negative bacteria; hence, a comprehensive study of AHLs, which are bacterial signal molecules, is required. The purpose of this review is to examine the effects of QS-mediated AHLs in many areas by looking at them from a different perspectives, such as clinic samples, food industry, aquatic life and wastewater treatment system.

Effect of hydrodynamic cavitation water treatment on Pseudomonas aeruginosa quorum-sensing molecules

Hydrodynamic cavitation treatment was used for the functional inactivation of quorum-sensing lactone molecules of Pseudomonas aeruginosa. Hydroxyl radicals formed as well as the shear effects during the cavitation process induced the inactivation of the signal molecules through hydrolysis reaction coupled with bacterial destruction. Concentration of two different types of homoserine lactones(HSL) molecules was tested after the treatment at various rotational speeds. It was found that the strongest effects can be achieved at speeds > 2000 rpm. This value is considered as an onset speed of dominant cavitation, and it is in agreement with literature data. The experimental trends were in agreement with the calculations based on the finite element modelling, which show a significant increase in average shear stress at higher rotational speeds. Overall, the work has demonstrated the possible effects of hydrodynamic cavitation on the quorum-sensing molecules of Pseudomonas aeruginosa for the first time.

BIOFILM FORMATION AND QUORUM SENSING ANALYSIS OF UROPATHOGENIC MULTIDRUG RESISTANCE ESCHERICHIA COLI

Objective: Escherichia coli (E. coli) are gram-negative facultative anaerobes which are commonly found in the lower intestine. Biofilm production in E. coli promotes colonization and leads to an increase rate of infections, and such infections may be difficult to treat as they exhibit multidrug resistance (MDR).&#x0D; Methods: 50 strains of uropathogenic E. coli were collected from Clinical Microbiology laboratory at Saveetha medical college and hospital for a time period of 3 mo. Strains were identified by conventional biochemical methods. Biofilm formation and quorum sensing analysis were performed by the Microtitre plate method and Thin Layer Chromatography method (TLC), respectively.&#x0D; Results: In this study, 46 (92%) of E. coli strains were strong, 3(6%) were intermediate and 1(2%) were weak biofilm producers. From TLC analysis, 34 (68%) of the strains produced Acyl Homoserine Lactone molecules. Out of which, 16 isolates were shown unknown analytes of Retardation factor (Rf) value greater than 1. The Rf values identified were 3 unsubstituted C4 (5), 3 unsubstituted C6 (3), 3 oxo C8 (3), 3 oxo C4 (4), 3 oxo C6 (2), 3 oxo C1 (1).&#x0D; Conclusion: In this study, 100% of isolates were biofilm producers. Of which 18 strains produced known Acyl Homoserine Lactone molecules and 16 isolates produced unknown analytes. Thus, quorum sensing molecules plays a major role in biofilm formation.

Attenuation of quorum sensing mediated virulence factors production and biofilm formation in Pseudomonas aeruginosa PAO1 by Colletotrichum gloeosporioides HM3

Signal dependent microbial communication in Pseudomonas aeruginosa PAO1 is a typical phenomenon mediated by acyl homo-serine lactone molecules that helps in developing biofilm and enhance antibiotic resistance. Microbial sources provide insight to the hidden treasure of secondary metabolites, and these structurally diversified chemical motifs can be used as antimicrobial and anti-infective agents. In the present study, endophytic fungus, Colletotrichum gloeosporioides HM3 isolated from Carica papaya leaves was explored for anti-infective potential against P. aeruginosa PAO1. The crude extract of C. gloeosporioides HM3 displayed bacteriostatic effect on P. aeruginosa PAO1 growth at 750 μg/ml concentration. A significant decline was observed in the production of quorum sensing regulated virulence factors, i.e. 56.32%, 62.54%, and 66.67% of pyocyanin, chitinase, and elastase enzyme, respectively. A drastic reduction in pathogenic determinant behaviour after treatment with crude extract of C. gloeosporioides HM3 i.e. EPS, rhamnolipid, and HCN production was noted. Light microscopy and CLSM analysis revealed that fungal extract treatment has reduced bacterial ability to form dense biofilm architecture. In silico analysis demonstrated the binding efficiency of bioactive compound, 4-(2,3-dimethoxybenzylidene)-3-methyl-1-(4-nitrophenyl)-2-pyrazolin-5-one, which is equipotent to the natural ligand and displayed a docking score of −5.436 kcal/mol with QS transcriptional regulator (LasR). Whereas the compound Acetamide, n-[tetrahydro-3-(phenylmethyl) thieno [3,4-d]thiazol-2 (3 h)-ylidene]-, s,s-dioxide exhibits a docking score of −4.088 kcal/mol (LasR) and −1.868 kcal/mol (RhlR) with cognate receptor proteins. Henceforth, the research report suggests C. gloeosporioides HM3 derived metabolites could be considered as a potential inhibitors of QS regulated virulence factors and biofilm production in P. aeruginosa PAO1.

QUORUM SENSING ANALYSIS AND EFFECT OF BACTERIOCIN IN CONTROLLING THE BIOFILM FORMATION OF PSEUDOMONAS AERUGINOSA

Objective: Pseudomonas aeruginosa is the commonest causative agent of Hospital Acquired Infection (HAI). Resistance of Pseudomonas aeruginosa towards disinfectants and antibiotics is high when compared to other organisms. There are various reviews on antibacterial effect of herbal extracts and nanoparticles against Pseudomonas aeruginosa. Thus, this study aims to prove the effectiveness of bacteriocin against Pseudomonas aeruginosa, which may help in benefiting the health care center by replacing normal disinfectants.&#x0D; Methods: 100 strains of Pseudomonas aeruginosa were collected from different patients, with a study period of 6 mo. Ammonium sulfate precipitation method was used to extract bacteriocin and its efficiency was checked by paper disc diffusion assay. Biofilm formation assay and quorum sensing analysis was performed by Microtitre plate methods and Thin Layer Chromatography (TLC), respectively.&#x0D; Results: In this study, 91%of P. aeruginosa strains were strong, 8% were intermediate, and 1% were weak biofilm producers. From TLC analysis, 67% of the strains produced Acyl Homoserine Lactone molecules. Out of which, 49% has shown unknown analytes of Retardation factor (Rf) value greater than 1. The Rf values identified were 3 unsubstitutedC4 (5%), 3 unsubstituted C6 (4%), 3 oxo C8 (3%), 3 oxo C4 (3%), 3 oxo C6 (2%), 3 oxo C1 (1%). Biofilm production, before and after bacteriocin exposure, was proved significant by paired t-test.&#x0D; Conclusion: Quorum sensing was confirmed to play a major role in biofilm formation. As bacteriocin was found to be effective in controlling the biofilm formation, it can be incorporated in any disinfectant, which helps in controlling the transmission of infection caused by Pseudomonas aeruginosa.

Diversity of Acyl Homoserine Lactone Molecules in Anaerobic Membrane Bioreactors Treating Sewage at Psychrophilic Temperatures.

This study explores the types of acyl homoserine lactone (AHL) and their concentrations in different compartments of different conventional anaerobic bioreactors: (i) an upflow anaerobic membrane bioreactor (UAnMBR, biofilm/mixed liquor (sludge)); (ii) an anaerobic membrane bioreactor (AnMBR, biofilm/mixed liquor (sludge)); and (iii) an upflow sludge blanket (UASB, sludge only), all operating at 15 °C. Ten types of the AHL, namely C4-HSL, 3-oxo-C4-HSL, C6-HSL, 3-oxo-C6-HSL, C8-HSL, 3-oxo-C8-HSL, C10-HSL, 3-oxo-C10-HSL, C12-HSL, and 3-oxo-C12-HSL, which were investigated in this study, were found in UAnMBR and UASB, whilst only six of them (C4-HSL, 3-oxo-C4-HSL, C8-HSL, C10-HSL, 3-oxo-C10-HSL, and C12-HSL) were found in AnMBR. Concentrations of total AHL were generally higher in the biofilm than the sludge for both membrane bioreactors trialed. C10-HSL was the predominant AHL found in all reactors (biofilm and sludge) followed by C4-HSL and C8-HSL. Overall, the UAnMBR biofilm and sludge had 10-fold higher concentrations of AHL compared to the AnMBR. C10-HSL was only correlated with bacteria (p < 0.05), whilst other types of AHL were correlated with both bacteria and archaea. This study improves our understanding of AHL-mediated Quorum Sensing (QS) in the biofilms/sludge of UAnMBR and AnMBR, and provides new information that could contribute to the development of quorum quenching anti-fouling strategies in such systems.

Growth stimulatory effect of AHL producing Serratia spp. from potato on homologous and non-homologous host plants

Plant growth promoting rhizobacteria are known to improve plant performance by developing healthy and productive interactions with the host plants. These associations may be symbiotic or asymbiotic depending upon the genetic potential of the resident microbe and promiscuity of the host. Present study describes the potential of two Serratia spp. strains for promotion of plant growth in homologous as well as non-homologous hosts. The strains KPS-10 and KPS-14; native to potato rhizosphere belong to genus Serratia based on 16S rRNA gene sequences (accession no. LN831934 and LN831937 respectively) and contain multiple plant growth promoting properties along-with the production of quorum sensing acyl homoserine lactone (AHL) molecules. Both Serratia spp. strains showed solubilization of inorganic tri-calcium phosphate while KPS-14 also exhibited phytase activity (1.98 10−10 kcat). KPS-10 showed higher P-solubilization activity (128.5 μg/mL), IAA production (8.84 μg/mL), antifungal activity and also showed the production of two organic acids i.e., gluconic acid and lactic acid. Both strains produced three common AHLs: C6-HSL, 3oxo-C10-HSL, 3oxo-C12-HSL while some strain-specific AHLs (3OH-C5-HSL, 3OH-C6-HSL, C10-HSL specific to KPS-10 and 3OH-C6-HSL, C8-HSL, 3oxo-C9-HSL, 3OH-C9-HSL specific to KPS-14). Strains showed roots and rhizosphere colonization of potato and other non-homologous hosts up to one month. In planta AHLs-detection confirmed a likely role of AHLs during seedling growth and development where both extracted AHLs or bacteria inoculated roots showed extensive root hair. A significant increase in root/shoot lengths, root/ shoot fresh weights, root/shoot dry weights was observed by inoculation in different hosts. PGP-characteristics along with the AHLs-production signify the potential of both strains as candidate for the development of bio-inoculum for potato crop in specific and other crops in general. This inoculum will not only reduce the input of chemical fertilizer to the environment but also improve soil quality and plant growth.

NHC-Catalyzed Cascade Reaction between β-Methyl Enals and Dienones for Quick Construction of Complex Multicyclic Lactones.

A NHC-promoted cascade reaction between β-methyl enal and dienone is developed for quick access to multicyclic lactone molecules bearing quaternary chiral carbon centers. Our study constitutes the first 1,6-addition of the acylazolium vinyl enolate γ-carbon via NHC catalysis and provides rapid access to complex lactone molecules that are otherwise difficult to prepare. The structurally sophisticated lactone products bearing up to four fused ring structures are afforded in up to quantitative yields with good to excellent enantioselectivities.

Biofunctionalization of Silver Nanoparticles With Lactonase Leads to Altered Antimicrobial and Cytotoxic Properties.

Background: N-acylated homoserine lactone lactonase which cleave the Acyl homoserine lactone molecules produced by biofilm-forming pathogens and silver nano-particles (AgNPs), are known for their antibacterial effect against several Gram-positive and Gram-negative bacteria. In this study, AgNPs were coated with N-acylated homoserine lactonase protein (AgNPs-AiiA) isolated from Bacillus sp. ZA12.Results: The AgNPs-AiiA complex was characterized by UV-visible spectra, Dynamic light Scattering, Fourier transform infrared spectroscopy (FTIR), and Field Emission Scanning Electron Microscope (Fe-SEM). The synthesized nano-particles were found to be spherical in shape and had an approximate size of 22.4 nm. Treatment with AiiA coated AgNPs showed a significant reduction in exopolysaccharide production, metabolic activity, cell surface hydrophobicity of bacterial cells, and anti-biofilm activity against multidrug-resistant K. pneumoniae as compared to treatment with AiiA protein and neat AgNPs. AgNPs-AiiA complex exhibited potent antibiofilm activity at sub-optimal concentration of 14.4 μg/mL without being harmful to the macrophages and to the various tissues including kidney, liver, spleen and lungs of BALB/c mice upon intra-venous administration.Conclusion: It is concluded that at a concentration of 14.4 μg/mL, AgNPs coated with AiiA kill bacteria without harming the host tissue and provides a suitable template to design novel anti-biofilm drug to circumvent the issue of drug resistance.

Signal Disruption Leads to Changes in Bacterial Community Population.

The disruption of bacterial signaling (quorum quenching) has been proven to be an innovative approach to influence the behavior of bacteria. In particular, lactonase enzymes that are capable of hydrolyzing the N-acyl homoserine lactone (AHL) molecules used by numerous bacteria, were reported to inhibit biofilm formation, including those of freshwater microbial communities. However, insights and tools are currently lacking to characterize, understand and explain the effects of signal disruption on complex microbial communities. Here, we produced silica capsules containing an engineered lactonase that exhibits quorum quenching activity. Capsules were used to design a filtration cartridge to selectively degrade AHLs from a recirculating bioreactor. The growth of a complex microbial community in the bioreactor, in the presence or absence of lactonase, was monitored over a 3-week period. Dynamic population analysis revealed that signal disruption using a quorum quenching lactonase can effectively reduce biofilm formation in the recirculating bioreactor system and that biofilm inhibition is concomitant to drastic changes in the composition, diversity and abundance of soil bacterial communities within these biofilms. Effects of the quorum quenching lactonase on the suspension community also affected the microbial composition, suggesting that effects of signal disruption are not limited to biofilm populations. This unexpected finding is evidence for the importance of signaling in the competition between bacteria within communities. This study provides foundational tools and data for the investigation of the importance of AHL-based signaling in the context of complex microbial communities.