Quorum quenching enzymes and their application in degrading signal molecules to block quorum sensing-dependent infection

Benefits of fungal-to-bacterial quorum quenching as anti-biofouling strategy in membrane bioreactors for wastewater treatment and water reuse

This study addresses membrane biofouling in membrane bioreactors (MBRs) by exploring fungal-to-bacterial quorum quenching (QQ) strategies. While most research has been focused on bacterial-to-bacterial QQ tactics, this study identified fungal strain Vanrija sp. MS1, which is capable of degrading N-acyl-homoserine lactones (signaling molecules of Gram-negative bacteria). To determine the benefits of fungal over bacterial strains, after immobilization on fluidizing spherical beads in an MBR, MS1 significantly reduced the fouling rate by 1.8-fold compared to control MBR, decreased extracellular polymeric substance levels in the biofilm during MBR operation, and favorably changed microbial community and bacterial network, resulting in biofouling mitigation. It is noteworthy that, unlike Rhodococcus sp. BH4, MS1 enhanced QQ activity when switching from neutral to acidic conditions. These results suggest that MS1 has the potential for the effective treatment of acidic industrial wastewater sources such as semiconductor and secondary battery wastewater using MBRs.

Bacterial-fungal crosstalk is defined by a fungal lactone mycotoxin and its degradation by a bacterial lactonase

Bacteria, fungi, and mammals contain lactonases that can degrade the Gram-negative bacterial quorum sensing (QS) molecules N-acyl homoserine lactones (AHLs). AHLs are critical for bacteria to coordinate gene expression and pathogenicity with population density. However, AHL-degrading lactonases present variable substrate ranges, including degradation of the Pencillium expansum lactone mycotoxin patulin. We selected Erwinia spp. as our model bacteria to further investigate this interaction. We find both native apple microbiome Erwinia spp. and the fruit tree pathogen Erwinia amylovora to be inhibited by patulin. At patulin concentrations that inhibited E. amylovora growth, expression of E. amylovora lactonase encoded by EaaiiA was increased. EaAiiA demonstrated the ability to degrade patulin in vitro, as well, as in vivo where it reduced apple disease and patulin production by P. expansum. Fungal-bacterial co-cultures revealed that the E. amylovora Δeaaiia strain failed to protect apples from P. expansum infections, which contained significant amounts of patulin. Our results suggest that bacterial lactonase production can modulate the pathogenicity of P. expansum in response to the secretion of toxic patulin.

IMPORTANCE

Chemical signaling in the microbial world facilitates the regulation of gene expression as a function of cell population density. This is especially true for the Gram-negative bacterial signal N-acyl homoserine lactone (AHL). Lactonases that deactivate AHLs have attracted a lot of attention because of their antibacterial potential. However, the involvement of these enzymes in inhibiting fungal pathogens and the potential role of these enzymes in bacterial-fungal interactions are unknown. Here, we find that a bacterial enzyme involved in the degradation of AHLs is also induced by and degrades the fungal lactone mycotoxin, patulin. This work supports the potential use of bacterial enzymes and/or the producing bacteria in controlling the post-harvest fruit disease caused by the patulin-producing fungus Penicillium expansum.

Molecular insights into PGPR fluorescent Pseudomonads complex mediated intercellular and interkingdom signal transduction mechanisms in promoting plant's immunity

The growth-promoting and immune modulatory properties of different strains of plant growth promoting rhizobacteria (PGPR) fluorescent Pseudomonads complex (PFPC) can be explored to combat food security challenges. These PFPC prime plants through induced systemic resistance, fortify plants to overcome future pathogen-mediated vulnerability by eliciting robust systemic acquired resistance through regulation by nonexpressor of pathogenesis-related genes 1. Moreover, outer membrane vesicles released from Pseudomonas fluorescens also elicit a broad spectrum of immune responses, presenting a rapid viable alternative to whole cells. Thus, PFPC can help the host to maintain an equilibrium between growth and immunity, ultimately leads to increased crop yield.

Quorum Quenching Potential of Reyranella sp. Isolated from Riverside Soil and Description of Reyranella humidisoli sp. nov

Quorum quenching refers to any mechanism that inhibits quorum sensing processes. In this study, quorum quenching activity among bacteria inhabiting riverside soil was screened, and a novel Gram-stain-negative, rod shaped bacterial strain designated MMS21-HV4-11T, which showed the highest level of quorum quenching activity, was isolated and subjected to further analysis. Strain MMS21-HV4-11T could be assigned to the genus Reyranella of Alphaproteobacteria based on the 16S rRNA gene sequence, as the strain shared 98.74% sequence similarity with Reyranella aquatilis seoho-37T, and then 97.87% and 97.80% sequence similarity with Reyranella soli KIS14-15T and Reyranella massiliensis 521T, respectively. The decomposed N-acyl homoserine lactone was restored at high concentrations under acidic conditions, implying that lactonase and other enzyme(s) are responsible for quorum quenching. The genome analysis indicated that strain MMS21-HV4-11T had two candidate genes for lactonase and one for acylase, and expected protein structures were confirmed. In the quorum sensing inhibition assay using a plant pathogen Pectobacterium carotovorum KACC 14888, development of soft rot was significantly inhibited by strain MMS21-HV4-11T. Besides, the swarming motility by Pseudomonas aeruginosa PA14 was significantly inhibited in the presence of strain MMS21-HV4-11T. Since the isolate did not display direct antibacterial activity against either of these species, the inhibition was certainly due to quorum quenching activity. In an extended study with the type strains of all known species of Reyranella, all strains were capable of degrading N-acyl homoserine lactones (AHLs), thus showing quorum quenching potential at the genus level. This is the first study on the quorum quenching potential and enzymes responsible in Reyranella. In addition, MMS21-HV4-11T could be recognized as a new species through taxonomic characterization, for which the name Reyranella humidisoli sp. nov. is proposed (type strain = MMS21-HV4-11 T = KCTC 82780 T = LMG 32365T).

Monomeric Esterase: Insights into Cooperative Behavior, Hysteresis/Allokairy

Herein, we present a novel esterase enzyme, Ade1, isolated from a metagenomic library of Amazonian dark earths soils, demonstrating its broad substrate promiscuity by hydrolyzing ester bonds linked to aliphatic groups. The three-dimensional structure of the enzyme was solved in the presence and absence of substrate (tributyrin), revealing its classification within the α/β-hydrolase superfamily. Despite being a monomeric enzyme, enzymatic assays reveal a cooperative behavior with a sigmoidal profile (initial velocities vs substrate concentrations). Our investigation brings to light the allokairy/hysteresis behavior of Ade1, as evidenced by a transient burst profile during the hydrolysis of substrates such as p-nitrophenyl butyrate and p-nitrophenyl octanoate. Crystal structures of Ade1, coupled with molecular dynamics simulations, unveil the existence of multiple conformational structures within a single molecular state (E̅1). Notably, substrate binding induces a loop closure that traps the substrate in the catalytic site. Upon product release, the cap domain opens simultaneously with structural changes, transitioning the enzyme to a new molecular state (E̅2). This study advances our understanding of hysteresis/allokairy mechanisms, a temporal regulation that appears more pervasive than previously acknowledged and extends its presence to metabolic enzymes. These findings also hold potential implications for addressing human diseases associated with metabolic dysregulation.

An In-Depth Study on the Inhibition of Quorum Sensing by Bacillus velezensis D-18: Its Significant Impact on Vibrio Biofilm Formation in Aquaculture

Amid growing concerns about antibiotic resistance, innovative strategies are imperative in addressing bacterial infections in aquaculture. Quorum quenching (QQ), the enzymatic inhibition of quorum sensing (QS), has emerged as a promising solution. This study delves into the QQ capabilities of the probiotic strain Bacillus velezensis D-18 and its products, particularly in Vibrio anguillarum 507 communication and biofilm formation. Chromobacterium violaceum MK was used as a biomarker in this study, and the results confirmed that B. velezensis D-18 effectively inhibits QS. Further exploration into the QQ mechanism revealed the presence of lactonase activity by B. velezensis D-18 that degraded both long- and short-chain acyl homoserine lactones (AHLs). PCR analysis demonstrated the presence of a homologous lactonase-producing gene, ytnP, in the genome of B. velezensis D-18. The study evaluated the impact of B. velezensis D-18 on V. anguillarum 507 growth and biofilm formation. The probiotic not only controls the biofilm formation of V. anguillarum but also significantly restrains pathogen growth. Therefore, B. velezensis D-18 demonstrates substantial potential for preventing V. anguillarum diseases in aquaculture through its QQ capacity. The ability to disrupt bacterial communication and control biofilm formation positions B. velezensis D-18 as a promising eco-friendly alternative to conventional antibiotics in managing bacterial diseases in aquaculture.

Biofilm inhibition/eradication: exploring strategies and confronting challenges in combatting biofilm

Biofilms are complex communities of microorganisms enclosed in a self-produced extracellular matrix, posing a significant threat to different sectors, including healthcare and industry. This review provides an overview of the challenges faced due to biofilm formation and different novel strategies that can combat biofilm formation. Bacteria inside the biofilm exhibit increased resistance against different antimicrobial agents, including conventional antibiotics, which can lead to severe problems in livestock and animals, including humans. In addition, biofilm formation also imposes heavy economic pressure on industries. Hence it becomes necessary to explore newer alternatives to eradicate biofilms effectively without applying selection pressure on the bacteria. Excessive usage of antibiotics may also lead to an increase in the number of resistant strains as bacteria employ an advanced antimicrobial resistance mechanism. This review provides insight into multifaceted technologies like quorum sensing inhibition, enzymes, antimicrobial peptides, bacteriophage, phytocompounds, and nanotechnology to neutralize biofilms without developing antimicrobial resistance (AMR). Furthermore, it will pave the way for developing newer therapeutic agents to deal with biofilms more efficiently.

Disruption of Communication: Recent Advances in Antibiofilm Materials with Anti-Quorum Sensing Properties

Biofilm contamination presents a significant threat to public health, the food industry, and aquatic/marine-related applications. In recent decades, although various methods have emerged to combat biofilm contamination, the intricate and persistent nature of biofilms makes complete eradication challenging. Therefore, innovative alternative solutions are imperative for addressing biofilm formation. Instead of solely focusing on the eradication of mature biofilms, strategically advantageous measures involve the delay or prevention of biofilm formation on surfaces. Quorum sensing, a communication system enabling bacteria to coordinate their behavior based on population density, plays a pivotal role in biofilm formation for numerous microbial species. Materials possessing antibiofilm properties that target quorum sensing have gained considerable attention for their potential to prevent biofilm formation. This Review consolidates recent research progress on the utilization of materials with antiquorum sensing properties for combating biofilm formation. These materials can be categorized into three distinct types: (i) antibiofilm nanomaterials, (ii) antibiofilm surfaces, and (iii) antibiofilm hydrogels with antiquorum sensing capabilities. Finally, the Review concludes with a brief discussion of current challenges and outlines potential avenues for future research.

Antibiotic Resistant Biofilms and the Quest for Novel Therapeutic Strategies

Antimicrobial resistance (AMR) is one of the major leading causes of death around the globe. Present treatment pipelines are insufficient to overcome the critical situation. Prominent biofilm forming human pathogens which can thrive in infection sites using adaptive features results in biofilm persistence. Considering the present scenario, prudential investigations into the mechanisms of resistance target them to improve antibiotic efficacy is required. Regarding this, developing newer and effective treatment options using edge cutting technologies in medical research is the need of time. The reasons underlying the adaptive features in biofilm persistence have been centred on different metabolic and physiological aspects. The high tolerance levels against antibiotics direct researchers to search for novel bioactive molecules that can help combat the problem. In view of this, the present review outlines the focuses on an opportunity of different strategies which are in testing pipeline can thus be developed into products ready to use.

Deciphering agr quorum sensing in Staphylococcus aureus: insights and therapeutic prospects

The emergence of superbugs like methicillin-resistant Staphylococcus aureus exposed the limitations of treating microbial infections using antibiotics. At present, the discovery of novel and convincing therapeutic methods are being executed increasingly as possible substitutes to conventional antibiotic therapies. The quorum sensing helps Staphylococcus aureus become more viable through their signaling mechanisms. In recent years, targeting the prominent factors of quorum sensing has obtained remarkable attention as a futuristic approach to dealing with bacterial pathogenicity. The standard antibiotic therapy intends to inhibit the organism by targeting specific molecules and afford a chance for the evolution of antibiotic resistance. This prompts the development of novel therapeutic strategies like inhibiting quorum sensing that can limit bacterial virulence by decreasing the selective pressure, thereby restricting antibiotic resistance evolution. This review furnishes new insights into the accessory gene regulator quorum sensing in Staphylococcus aureus and its inhibition by targeting the genes that regulate the operon. Further, this review comprehensively explores the inhibitors reported up to date and their specific targets and discusses their potentially ineffective alternative therapy against methicillin-resistant Staphylococcus aureus.

Thermostable Lactonases Inhibit Pseudomonas aeruginosa Biofilm: Effect In Vitro and in Drosophila melanogaster Model of Chronic Infection

Pseudomonas aeruginosa is one of the six antimicrobial-resistant pathogens known as "ESKAPE" that represent a global threat to human health and are considered priority targets for the development of novel antimicrobials and alternative therapeutics. The virulence of P. aeruginosa is regulated by a four-chemicals communication system termed quorum sensing (QS), and one main class of QS signals is termed acylhomoserine lactones (acyl-HSLs), which includes 3-Oxo-dodecanoil homoserine lactone (3-Oxo-C12-HSL), which regulates the expression of genes implicated in virulence and biofilm formation. Lactonases, like Paraoxonase 2 (PON2) from humans and the phosphotriesterase-like lactonases (PLLs) from thermostable microorganisms, are able to hydrolyze acyl-HSLs. In this work, we explored in vitro and in an animal model the effect of some lactonases on the production of Pseudomonas virulence factors. This study presents a model of chronic infection in which bacteria were administered by feeding, and Drosophila adults were treated with enzymes and the antibiotic tobramycin, alone or in combination. In vitro, we observed significant effects of lactonases on biofilm formation as well as effects on bacterial motility and the expression of virulence factors. The treatment in vivo by feeding with the lactonase SacPox allowed us to significantly increase the biocidal effect of tobramycin in chronic infection.

Selected strategies to fight pathogenic bacteria

Natural products and analogues are a source of antibacterial drug discovery. Considering drug resistance levels emerging for antibiotics, identification of bacterial metalloenzymes and the synthesis of selective inhibitors are interesting for antibacterial agent development. Peptide nucleic acids are attractive antisense and antigene agents representing a novel strategy to target pathogens due to their unique mechanism of action. Antisense inhibition and development of antisense peptide nucleic acids is a new approach to antibacterial agents. Due to the increased resistance of biofilms to antibiotics, alternative therapeutic options are necessary. To develop antimicrobial strategies, optimised in vitro and in vivo models are needed. In vivo models to study biofilm-related respiratory infections, device-related infections: ventilator-associated pneumonia, tissue-related infections: chronic infection models based on alginate or agar beads, methods to battle biofilm-related infections are discussed. Drug delivery in case of antibacterials often is a serious issue therefore this review includes overview of drug delivery nanosystems.

Biocontrol mechanisms of Bacillus: Improving the efficiency of green agriculture

Species of the genus Bacillus have been widely used for the biocontrol of plant diseases in the demand for sustainable agricultural development. New mechanisms underlying Bacillus biocontrol activity have been revealed with the development of microbiome and microbe-plant interaction research. In this review, we first briefly introduce the typical Bacillus biocontrol mechanisms, such as the production of antimicrobial compounds, competition for niches/nutrients, and induction of systemic resistance. Then, we discussed in detail the new mechanisms of pathogen quorum sensing interference and reshaping of the soil microbiota. The "cry for help" mechanism was also introduced, in which plants can release specific signals under pathogen attack to recruit biocontrol Bacillus for root colonization against invasion. Finally, two emerging strategies for enhancing the biocontrol efficacy of Bacillus agents, including the construction of synthetic microbial consortia and the application of rhizosphere-derived prebiotics, were proposed.

Efficacy of ceftiofur N-acyl homoserine lactonase niosome in the treatment of multi-resistant Klebsiella pneumoniae in broilers

In this study, the efficiency of the ceftiofur N-acyl homoserine lactonase niosome against multi-resistant Klebsiella pneumoniae in broilers was evaluated. Fifty-six K. pneumoniae isolates previously recovered from different poultry and environmental samples were screened for the ahlK gene. The lactonase enzyme was extracted from eight quorum-quenching isolates. The niosome was formulated, characterized, and tested for minimal inhibitory concentration (MIC) and cytotoxicity. Fourteen-day-old chicks were assigned to six groups: groups Ӏ and П served as negative and positive controls, receiving saline and K. pneumoniae solutions, respectively. In groups Ш and IV, ceftiofur and niosome were administrated intramuscularly at a dose of 10 mg/kg body weight for five consecutive days, while groups V and VI received the injections following the K. pneumoniae challenge. Signs, mortality, and gross lesions were recorded. Tracheal swabs were collected from groups П, V, and VI for counting K. pneumoniae. Pharmacokinetic parameters were evaluated in four treated groups at nine-time points. The niosome was spherical and 56.5 ± 4.41 nm in size. The viability of Vero cells was unaffected up to 5 × MIC (2.4 gml-1). The niosome-treated challenged group showed mild signs and lesions with lower mortality and colony count than the positive control group. The maximum ceftiofur serum concentrations in treated groups were observed 2 h following administration. The elimination half-life in niosome-treated groups was longer than that reported in ceftiofur-treated groups. This is the first report of the administration of N-acyl homoserine lactonase for the control of multi-resistant K. pneumoniae infections in poultry.

Deciphering the mechanisms, hormonal signaling, and potential applications of endophytic microbes to mediate stress tolerance in medicinal plants

The global healthcare market in the post-pandemic era emphasizes a constant pursuit of therapeutic, adaptogenic, and immune booster drugs. Medicinal plants are the only natural resource to meet this by supplying an array of bioactive secondary metabolites in an economic, greener and sustainable manner. Driven by the thrust in demand for natural immunity imparting nutraceutical and life-saving plant-derived drugs, the acreage for commercial cultivation of medicinal plants has dramatically increased in recent years. Limited resources of land and water, low productivity, poor soil fertility coupled with climate change, and biotic (bacteria, fungi, insects, viruses, nematodes) and abiotic (temperature, drought, salinity, waterlogging, and metal toxicity) stress necessitate medicinal plant productivity enhancement through sustainable strategies. Plants evolved intricate physiological (membrane integrity, organelle structural changes, osmotic adjustments, cell and tissue survival, reclamation, increased root-shoot ratio, antibiosis, hypersensitivity, etc.), biochemical (phytohormones synthesis, proline, protein levels, antioxidant enzymes accumulation, ion exclusion, generation of heat-shock proteins, synthesis of allelochemicals. etc.), and cellular (sensing of stress signals, signaling pathways, modulating expression of stress-responsive genes and proteins, etc.) mechanisms to combat stresses. Endophytes, colonizing in different plant tissues, synthesize novel bioactive compounds that medicinal plants can harness to mitigate environmental cues, thus making the agroecosystems self-sufficient toward green and sustainable approaches. Medicinal plants with a host set of metabolites and endophytes with another set of secondary metabolites interact in a highly complex manner involving adaptive mechanisms, including appropriate cellular responses triggered by stimuli received from the sensors situated on the cytoplasm and transmitting signals to the transcriptional machinery in the nucleus to withstand a stressful environment effectively. Signaling pathways serve as a crucial nexus for sensing stress and establishing plants' proper molecular and cellular responses. However, the underlying mechanisms and critical signaling pathways triggered by endophytic microbes are meager. This review comprehends the diversity of endophytes in medicinal plants and endophyte-mediated plant-microbe interactions for biotic and abiotic stress tolerance in medicinal plants by understanding complex adaptive physiological mechanisms and signaling cascades involving defined molecular and cellular responses. Leveraging this knowledge, researchers can design specific microbial formulations that optimize plant health, increase nutrient uptake, boost crop yields, and support a resilient, sustainable agricultural system.

Biocontrol of biofilm forming Burkholderia cepacia using a quorum quenching crude lactonase enzyme extract from a marine Chromohalobacter sp. strain D23

Biofilm plays advantageous role in Burkholderia cepacia by exerting multi-drug resistance. As quorum sensing (QS) system regulates biofilm formation and pathogenicity in B. cepacia strains, quorum quenching (QQ) may be a novel strategy to control persistent B. cepacia infections. In these regards, 120 halophilic bacteria were isolated from marine sample and tested using Chromobacterium violaceum and C. violaceum CV026-based bioassays initially, showing reduced violacein synthesis by QQ enzyme by 6 isolates. Among them, Chromohalobacter sp. D23 significantly degraded both C6-homoserine lactone (C6-HSL) and C8-HSL due to potent lactonase activity, which was detected by C. violaceum CV026 biosensor. Further high-performance liquid chromatography (HPLC) study confirmed degradation of N-acyl homoserine lactones (N-AHLs) particularly C6-HSL and C8-HSL by crude lactonase enzyme. Chromohalobacter sp. D23 reduced biofilm formation in terms of decreased total biomass and viability in biofilm-embedded cells in B. cepacia significantly which was also evidenced by fluorescence microscopic images. An increase in antibiotic susceptibility of B. cepacia biofilm was achieved when crude lactonase enzyme of Chromohalobacter sp. strain D23 was combined with chloramphenicol (1-5 × MIC). Chromohalobacter sp. D23 also showed prominent decrease in QS-mediated synthesis of virulence factors such as extracellular polymeric substances (EPS), extracellular protease, and hemolysin in B. cepacia. Again crude lactonase enzyme of Chromohalobacter sp. strain D23 inhibited B. cepacia biofilm formation inside nasal oxygen catheters in vitro. Finally, antibiotic susceptibility test and virulence tests revealed sensitivity of Chromohalobacter sp. strain D23 against a wide range of conventional antibiotics as well as absence of gelatinolytic, hemolytic, and serum coagulating activities. Therefore, the current study shows potential quorum quenching as well as anti-biofilm activity of Chromohalobacter sp. D23 against B. cepacia.

Control of pathogenic bacteria using marine actinobacterial extract with antiquorum sensing and antibiofilm activity

OBJECTIVE

The objectives of this research were to screen the anti-quorum sensing and antibiofilm activity of marine actinobacteria, isolated from several aquatic environments in Indonesia against several pathogenic bacteria, such as Staphylococcus aureus, Bacillus cereus, Enterococcus faecalis, Vibrio cholerae, Salmonella Typhimurium, and Pseudomonas aeruginosa.

RESULTS

Ten out of 40 actinobacteria were found to have anti-quorum sensing activity against wild-type Chromobacterium violaceum (ATCC 12472); however, the validation assay showed that only eight of 10 significantly inhibited the quorum sensing system of Chromobacterium violaceum CV026. The crude actinobacteria extracts inhibited and disrupted biofilm formation produced by pathogens. The highest antibiofilm inhibition was discovered in isolates 11AC (90%), 1AC (90%), CW17 (84%), TB12 (94%), 20PM (85%), CW01 (93%) against Staphylococcus aureus, Bacillus cereus, Enterococcus faecalis, Vibrio cholerae, Salmonella Typhimurium, and Pseudomonas aeruginosa, respectively. The highest biofilm destruction activity was observed for isolate 1AC (77%), 20PM (85%), 16PM (72%), CW01 (73%), 18PM (82%), 16PM (63%) against Staphylococcus aureus, Bacillus cereus, Enterococcus faecalis, Vibrio cholerae, Salmonella Typhimurium, and Pseudomonas aeruginosa, respectively. Actinobacteria isolates demonstrated promising anti-quorum and/or antibiofilm activity, interfering with the biofilm formation of tested pathogens. Appropriate formulations of these extracts could be developed as effective disinfectants, eradicating biofilms in many industries.

Probiotic Supplementation as an Emerging Alternative to Chemical Therapeutics in Finfish Aquaculture: a Review

Aquaculture is a promising food sector to fulfil nutritional requirements of growing human population. Live weight aquaculture production reached up to 114.5 million tonnes in 2018 and it is further expected to grow by 32% by year 2030. Among total aquaculture production, major product harvested is finfish and its contribution has reached 46% in recent years. Frequent outbreaks of infectious diseases create obstacle in finfish production, result in economic losses to the farmers and threaten the sustainability of aquaculture industry itself. In spite of following the best management practices, the use of antibiotics, chemotherapeutics and phytochemicals often become the method of choice in finfish culture. Among these, phytochemicals have shown lesser effect in animal welfare while antibiotics and other chemotherapeutics have led to negative consequences like emergence of drug-resistant bacteria, and accumulation of residues in host and culture system, resulting in quality degradation of aqua products. Making use of probiotics as viable alternative has paved a way for sustainable aquaculture and minimise the use of antibiotics and other chemotherapeutics that pose adverse effect on host and culture system. This review paper elucidates the knowledge about antibiotics and other chemicals, compilation of probiotics and their effects on health status of finfish as well as overall culture environment. Besides, concoction of probiotics and prebiotics for simultaneous application has also been discussed briefly.

Preliminary indication of the role of AHL-dependent quorum sensing systems in calcium carbonate precipitation in Gram-negative bacteria

Numerous microbial species participate in precipitation of carbonates in various natural environments, including soils, geological formations, freshwater biofilms and oceans. Despite the geochemical interest of such a biomineralization process, its molecular mechanisms and adaptive aspects remain poorly known. Many Gram-negative bacteria use cell-to-cell communication systems relying on N-acylhomoserine lactone (AHLs) signal molecules to express certain phenotypic traits in a density-dependent manner, a phenomenon referred as to quorum-sensing (QS). In this work, bacterial isolates collected from cave and rhizosphere soil were analyzed to study the occurrence of the AHL-mediated QS in bacterial calcium carbonate (CaCO3) precipitation. To test the production of AHLs signal molecules, we cross-streaked Gram-negative calcifying strains, selected among the environmental strains studied, with the AHL-negative mutant Chromobacterium subtsugae strain CV026. Only Burkholderia ambifaria LMG 11351 was able to restore violacein production in CV026 among the tested strains. The constructed AHL-negative mutant of B. ambifaria LMG 11351 could not precipitate CaCO3 on B-4 agar. Scanning Electron Microscopy (SEM) analysis on CaCO3 crystals obtained in vitro shows crystals of different morphologies, calcified biofilms and bacteria in close contact with the precipitated crystals. In the inner layers of the bioliths deposited by B. ambifaria LMG 11351, a stream-like organization of the Burkholderia imprints was not detected by SEM. Our data provide preliminary evidence that the activation of AHL-regulated genes may be a prerequisite for in vitro bacterial carbonatogenesis, in some cases, confirming the specific role of bacteria as CaCO3 precipitating agents. We enhance the understanding of bacterial CaCO3 biomineralization and its potential biotechnology implications for QS-based strategies to enhance or decrease CaCO3 precipitation through specific bacterial processes. The AHL-negative mutant of B. ambifaria LMG 11351 (a well-known plant growth-promoting bacterium) could also be used to study plant-bacteria interactions. The adaptive role of bacterial CaCO3 biomineralization was also discussed.

The Effect of Maternal Probiotic or Synbiotic Supplementation on Sow and Offspring Gastrointestinal Microbiota, Health, and Performance

The increasing prevalence of antimicrobial-resistant pathogens has prompted the reduction in antibiotic and antimicrobial use in commercial pig production. This has led to increased research efforts to identify alternative dietary interventions to support the health and development of the pig. The crucial role of the GIT microbiota in animal health and performance is becoming increasingly evident. Hence, promoting an improved GIT microbiota, particularly the pioneer microbiota in the young pig, is a fundamental focus. Recent research has indicated that the sow's GIT microbiota is a significant contributor to the development of the offspring's microbiota. Thus, dietary manipulation of the sow's microbiota with probiotics or synbiotics, before farrowing and during lactation, is a compelling area of exploration. This review aims to identify the potential health benefits of maternal probiotic or synbiotic supplementation to both the sow and her offspring and to explore their possible modes of action. Finally, the results of maternal sow probiotic and synbiotic supplementation studies are collated and summarized. Maternal probiotic or synbiotic supplementation offers an effective strategy to modulate the sow's microbiota and thereby enhance the formation of a health-promoting pioneer microbiota in the offspring. In addition, this strategy can potentially reduce oxidative stress and inflammation in the sow and her offspring, enhance the immune potential of the milk, the immune system development in the offspring, and the sow's feed intake during lactation. Although many studies have used probiotics in the maternal sow diet, the most effective probiotic or probiotic blends remain unclear. To this extent, further direct comparative investigations using different probiotics are warranted to advance the current understanding in this area. Moreover, the number of investigations supplementing synbiotics in the maternal sow diet is limited and is an area where further exploration is warranted.

Quorum sensing signals: Aquaculture risk factor

Bacteria produce several virulence factors and cause massive mortality in fish and crustaceans. Abundant quorum sensing (QS) signals and high cell density are essentially required for the production of such virulence factors. Although several strategies have been developed to control aquatic pathogens through antibiotics and QS inhibition, the impact of pre‐existing QS signals in the aquatic environment has been overlooked. QS signals cause detrimental effects on mammalian cells and induce cell death by interfering with multiple cellular pathways. Moreover, QS signals not only function as a messenger, but also annihilate the functions of the host immune system which implies that QS signals should be designated as a major virulence factor. Despite QS signals' role has been well documented in mammalian cells, their impact on aquatic organisms is still at the budding stage. However, many aquatic organisms produce enzymes that degrade and detoxify such QS signals. In addition, physical and chemical factors also determine the stability of the QS signals in the aqueous environment. The balance between QS signals and existing QS signals degrading factors essentially determines the disease progression in aquatic organisms. In this review, we highlight the impact of QS signals on aquatic organisms and further discussed potential alternative strategies to control disease progression.

Glabridin Functions as a Quorum Sensing Inhibitor to Inhibit Biofilm Formation and Swarming Motility of Multidrug-Resistant Acinetobacter baumannii

Objective

Acinetobacter baumannii is a hazardous bacterium that causes hospital-acquired nosocomial infections, and the advent of multidrug-resistant A. baumannii (MDR-AB) strains is concerning. Novel antibacterial therapeutic strategies must be developed. The biological effects of glabridin on MDR-AB were investigated in this study.

Methods

The minimum inhibitory concentrations (MICs) of glabridin against eight clinical MDR-AB strains were determined using the broth microdilution technique. Crystal violet staining was used to assess biofilm development, which has significant contribution to bacterial resistance. Swarming motility was measured according to surface growth zone of MDR-AB on LB agar medium. qRT-PCR was used to evaluate the expression of quorum sensing genes abaI and abaR. Glabridin and routinely used therapeutic antimicrobial agents were tested for synergistic action using the checkerboard method.

Results

According to our findings, glabridin suppressed MDR-AB growth at high doses (512-1024 μg/mL). The 1/4 MIC of glabridin significantly decreased MDR-AB biofilm formation by 19.98% (P < 0.05), inhibited MDR-AB motility by 44.27% (P < 0.05), whereas the 1/2 MIC of glabridin dramatically reduced MDR-AB biofilm development by 27.43% (P < 0.01), suppressed MDR-AB motility by 50.64% (P < 0.05). Mechanistically, glabridin substantially downregulated the expression of quorum sensing-related genes abaI and abaR by up to 39.12% (P < 0.001) and 25.19% (P < 0.01), respectively. However, no synergistic effect between glabridin and antibacterial drugs was found.

Conclusion

Glabridin might be a quorum sensing inhibitor that inhibits MDR-AB biofilm development and swarming motility.

Biofilm Formation of Clostridioides difficile, Toxin Production and Alternatives to Conventional Antibiotics in the Treatment of CDI

Clostridioides difficile is considered a nosocomial pathogen that flares up in patients exposed to antibiotic treatment. However, four out of ten patients diagnosed with C. difficile infection (CDI) acquired the infection from non-hospitalized individuals, many of whom have not been treated with antibiotics. Treatment of recurrent CDI (rCDI) with antibiotics, especially vancomycin (VAN) and metronidazole (MNZ), increases the risk of experiencing a relapse by as much as 70%. Fidaxomicin, on the other hand, proved more effective than VAN and MNZ by preventing the initial transcription of RNA toxin genes. Alternative forms of treatment include quorum quenching (QQ) that blocks toxin synthesis, binding of small anion molecules such as tolevamer to toxins, monoclonal antibodies, such as bezlotoxumab and actoxumab, bacteriophage therapy, probiotics, and fecal microbial transplants (FMTs). This review summarizes factors that affect the colonization of C. difficile and the pathogenicity of toxins TcdA and TcdB. The different approaches experimented with in the destruction of C. difficile and treatment of CDI are evaluated.

Pseudomonas forestsoilum sp. nov. and P. tohonis biocontrol bacterial wilt by quenching 3-hydroxypalmitic acid methyl ester

Bacterial wilt caused by Ralstonia solanacearum ranks the second top important bacterial plant disease worldwide. It is also the most important bacterial disease threatening the healthy development of Casuarina equisetifolia protection forest. 3-hydroxypalmitic acid methyl ester (3-OH PAME) functions as an important quorum sensing (QS) signal regulating the expression of virulence genes in R. solanacearum, and has been regarded as an ideal target for disease prevention and control. To screen native microorganisms capable of degrading 3-OH PAME, samples of C. equisetifolia branches and forest soil were collected and cultured in the medium containing 3-OH PAME as the sole carbon source. Bacteria with over 85% degradation rates of 3-OH PAME after 7-day incubation were further separated and purified. As a result, strain Q1-7 isolated from forest soil and strain Q4-3 isolated from C. equisetifolia branches were obtained and identified as Pseudomonas novel species Pseudomonas forestsoilum sp. nov. and P. tohonis, respectively, according to whole genome sequencing results. The degradation efficiencies of 3-OH PAME of strains Q1-7 and Q4-3 were 95.80% and 100.00% at 48 h, respectively. Both strains showed high esterase activities and inhibited R. solanacearum exopolysaccharide (EPS) and cellulase production. Application of strains Q1-7 and Q4-3 effectively protects C. equisetifolia, peanut and tomato plants from infection by R. solanacearum. Findings in this study provide potential resources for the prevention and control of bacterial wilt caused by R. solanacearum, as well as valuable materials for the identification of downstream quenching genes and the research and development of quenching enzymes for disease control.

Genome taxonomy of the genus Thalassotalea and proposal of Thalassotalea hakodatensis sp. nov. isolated from sea cucumber larvae

The genus Thalassotalea is ubiquitous in marine environments, and up to 20 species have been described so far. A Gram-staining-negative, aerobic bacterium, designated strain PTE2T was isolated from laboratory-reared larvae of the Japanese sea cucumber Apostichopus japonicus. Phylogenetic analysis based on the 16S rRNA gene nucleotide sequences revealed that PTE2T was closely related to Thalassotalea sediminis N211T (= KCTC 42588T = MCCC 1H00116T) with 97.9% sequence similarity. ANI and in silico DDH values against Thalassotalea species were 68.5-77.0% and 19.7-24.6%, respectively, indicating the novelty of PTE2T. Based on genome-based taxonomic approaches, strain PTE2T (= JCM 34608T = KCTC 82592T) is proposed as a new species, Thalassotalea hakodatensis sp. nov.

Paraoxonase-1: How a xenobiotic detoxifying enzyme has become an actor in the pathophysiology of infectious diseases and cancer

Both infectious and non-infectious diseases can share common molecular mechanisms, including oxidative stress and inflammation. External factors, such as bacterial or viral infections, excessive calorie intake, inadequate nutrients, or environmental factors, can cause metabolic disorders, resulting in an imbalance between free radical production and natural antioxidant systems. These factors may lead to the production of free radicals that can oxidize lipids, proteins, and nucleic acids, causing metabolic alterations that influence the pathogenesis of the disease. The relationship between oxidation and inflammation is crucial, as they both contribute to the development of cellular pathology. Paraoxonase 1 (PON1) is a vital enzyme in regulating these processes. PON1 is an enzyme that is bound to high-density lipoproteins and protects the organism against oxidative stress and toxic substances. It breaks down lipid peroxides in lipoproteins and cells, enhances the protection of high-density lipoproteins against different infectious agents, and is a critical component of the innate immune system. Impaired PON1 function can affect cellular homeostasis pathways and cause metabolically driven chronic inflammatory states. Therefore, understanding these relationships can help to improve treatments and identify new therapeutic targets. This review also examines the advantages and disadvantages of measuring serum PON1 levels in clinical settings, providing insight into the potential clinical use of this enzyme.

A Look at Plant-Growth-Promoting Bacteria

Bacteria have been used to increase crop yields. For their application on crops, bacteria are provided in inoculant formulations that are continuously changing, with liquid- and solid-based products. Bacteria for inoculants are mainly selected from natural isolates. In nature, microorganisms that favor plants exhibit various strategies to succeed and prevail in the rhizosphere, such as biological nitrogen fixation, phosphorus solubilization, and siderophore production. On the other hand, plants have strategies to maintain beneficial microorganisms, such as the exudation of chemoattractanst for specific microorganisms and signaling pathways that regulate plant-bacteria interactions. Transcriptomic approaches are helpful in attempting to elucidate plant-microorganism interactions. Here, we present a review of these issues.

Quorum-quenching enzymes: Promising bioresources and their opportunities and challenges as alternative bacteriostatic agents in food industry

The problems of spoilage, disease, and biofilm caused by bacterial quorum-sensing (QS) systems have posed a significant challenge to the development of the food industry. Quorum-quenching (QQ) enzymes can block QS by hydrolyzing or modifying the signal molecule, making these enzymes promising new candidates for use as antimicrobials. With many recent studies of QQ enzymes and their potential to target foodborne bacteria, an updated and systematic review is necessary. Thus, the goals of this review were to summarize what is known about the effects of bacterial QS on the food industry; discuss the current understanding of the catalytic mechanisms of QQ enzymes, including lactonase, acylase, and oxidoreductase; and describe strategies for the engineering and evolution of QQ enzymes for practical use. In particular, this review focuses on the latest progress in the application of QQ enzymes in the field of food. Finally, the current challenges limiting the systematic application of QQ enzymes in the food industry are discussed to help guide the future development of these important enzymes.

Rapid start-up of partial nitrification reactor by exogenous AHLs and Vanillin combined with intermittent aeration

Quorum sensing (QS) and quorum quenching (QQ) are common phenomena in microbial systems and play an important role in the nitrification process. However, rapidly start up partial nitrification regulated by N-acyl-homoserine lactones (AHLs)-mediated QS or QQ has not been reported. Hence, we chose N-butyryl homoserine lactone (C₄-HSL) and N-hexanoyl homoserine lactone (C₆-HSL) as the representative AHLs, and Vanillin as the representative quorum sensing inhibitor (QSI) combined intermittent aeration to investigate their effects on the start-up process of partial nitrification. The start-up speed in the group with C₄-HSL or C₆-HSL addition was 1.42 or 1.26 times faster than that without addition, respectively. Meanwhile, the ammonium removal efficiency with C₄-HSL or C₆-HSL addition was increased by 13.87 % and 17.30 % than that of the control group, respectively. And, partial nitrification could maintain for a certain period without AHLs further addition. The increase of Nitrosomonas abundance and ammonia monooxygenase (AMO) activity, and the decrease of Nitrobacter abundance and nitrite oxidoreductase (NXR) activity were the reasons for the rapid start-up of partial nitrification in the AHLs groups. Vanillin addition reduced AMO and hydroxylamine oxidoreductase (HAO) activity, and increased Nitrobacter abundance and NXR activity, thus these were not conducive to achieving partial nitrification. Denitrifying bacteria (Hydrogenophaga, Thauera and Aquimonas) abundance increased in the Vanillin group. QS-related bacteria and gene abundance were elevated in the AHLs group, and reduced in the Vanillin group. Function prediction demonstrated that AHLs promoted the nitrogen cycle while Vanillin enhanced the carbon cycle. This exploration might provide a new technical insight into the rapid start-up of partial nitrification based on QS control.

Antimicrobial Resistance and Recent Alternatives to Antibiotics for the Control of Bacterial Pathogens with an Emphasis on Foodborne Pathogens

Antimicrobial resistance (AMR) is one of the most important global public health problems. The imprudent use of antibiotics in humans and animals has resulted in the emergence of antibiotic-resistant bacteria. The dissemination of these strains and their resistant determinants could endanger antibiotic efficacy. Therefore, there is an urgent need to identify and develop novel strategies to combat antibiotic resistance. This review provides insights into the evolution and the mechanisms of AMR. Additionally, it discusses alternative approaches that might be used to control AMR, including probiotics, prebiotics, antimicrobial peptides, small molecules, organic acids, essential oils, bacteriophage, fecal transplants, and nanoparticles.

The Role of Quorum Sensing Molecules in Bacterial-Plant Interactions

Quorum sensing (QS) is a system of communication of bacterial cells by means of chemical signals called autoinducers, which modulate the behavior of entire populations of Gram-negative and Gram-positive bacteria. Three classes of signaling molecules have been recognized, Al-1, Al-2, Al-3, whose functions are slightly different. However, the phenomenon of quorum sensing is not only concerned with the interactions between bacteria, but the whole spectrum of interspecies interactions. A growing number of research results confirm the important role of QS molecules in the growth stimulation and defense responses in plants. Although many of the details concerning the signaling metabolites of the rhizosphere microflora and plant host are still unknown, Al-1 compounds should be considered as important components of bacterial-plant interactions, leading to the stimulation of plant growth and the biological control of phytopathogens. The use of class 1 autoinducers in plants to induce beneficial activity may be a practical solution to improve plant productivity under field conditions. In addition, researchers are also interested in tools that offer the possibility of regulating the activity of autoinducers by means of degrading enzymes or specific inhibitors (QSI). Current knowledge of QS and QSI provides an excellent foundation for the application of research to biopreparations in agriculture, containing a consortia of AHL-producing bacteria and QS inhibitors and limiting the growth of phytopathogenic organisms.

A novel bacterial strain Burkholderia sp. F25 capable of degrading diffusible signal factor signal shows strong biocontrol potential

Vast quantities of synthetic pesticides have been widely applied in various fields to kill plant pathogens, resulting in increased pathogen resistance and decreased effectiveness of such chemicals. In addition, the increased presence of pesticide residues affects living organisms and the environment largely on a global scale. To mitigate the impact of crop diseases more sustainably on plant health and productivity, there is a need for more safe and more eco-friendly strategies as compared to chemical prevention. Quorum sensing (QS) is an intercellular communication mechanism in a bacterial population, through which bacteria adjust their population density and behavior upon sensing the levels of signaling molecules in the environment. As an alternative, quorum quenching (QQ) is a promising new strategy for disease control, which interferes with QS by blocking intercellular communication between pathogenic bacteria to suppress the expression of disease-causing genes. Black rot caused by Xanthomonas campestris pv. campestris (Xcc) is associated with the diffusible signal factor (DSF). As detailed in this study, a new QQ strain F25, identified as Burkholderia sp., displayed a superior ability to completely degrade 2 mM of DSF within 72 h. The main intermediate product in the biodegradation of DSF was identified as n-decanoic acid, based on gas chromatography-mass spectrometry (GC-MS). A metabolic pathway for DSF by strain F25 is proposed, based on the chemical structure of DSF and its intermediates, demonstrating the possible degradation of DSF via oxidation-reduction. The application of strain F25 and its crude enzyme as biocontrol agents significantly attenuated black rot caused by Xcc, and inhibited tissue maceration in the host plant Raphanus sativus L., without affecting the host plant. This suggests that agents produced from strain F25 and its crude enzyme have promising applications in controlling infectious diseases caused by DSF-dependent bacterial pathogens. These findings are expected to provide a new therapeutic strategy for controlling QS-mediated plant diseases.

Endophytes and their potential in biotic stress management and crop production

Biotic stress is caused by harmful microbes that prevent plants from growing normally and also having numerous negative effects on agriculture crops globally. Many biotic factors such as bacteria, fungi, virus, weeds, insects, and nematodes are the major constrains of stress that tends to increase the reactive oxygen species that affect the physiological and molecular functioning of plants and also led to the decrease in crop productivity. Bacterial and fungal endophytes are the solution to overcome the tasks faced with conventional farming, and these are environment friendly microbial commodities that colonize in plant tissues without causing any damage. Endophytes play an important role in host fitness, uptake of nutrients, synthesis of phytohormone and diminish the injury triggered by pathogens via antibiosis, production of lytic enzymes, secondary metabolites, and hormone activation. They are also reported to help plants in coping with biotic stress, improving crops and soil health, respectively. Therefore, usage of endophytes as biofertilizers and biocontrol agent have developed an eco-friendly substitute to destructive chemicals for plant development and also in mitigation of biotic stress. Thus, this review highlighted the potential role of endophytes as biofertilizers, biocontrol agent, and in mitigation of biotic stress for maintenance of plant development and soil health for sustainable agriculture.

Bioengineering Approaches to Fight against Orthopedic Biomaterials Related-Infections

One of the most serious complications following the implantation of orthopedic biomaterials is the development of infection. Orthopedic implant-related infections do not only entail clinical problems and patient suffering, but also cause a burden on healthcare care systems. Additionally, the ageing of the world population, in particular in developed countries, has led to an increase in the population above 60 years. This is a significantly vulnerable population segment insofar as biomaterials use is concerned. Implanted materials are highly susceptible to bacterial and fungal colonization and the consequent infection. These microorganisms are often opportunistic, taking advantage of the weakening of the body defenses at the implant surface–tissue interface to attach to tissues or implant surfaces, instigating biofilm formation and subsequent development of infection. The establishment of biofilm leads to tissue destruction, systemic dissemination of the pathogen, and dysfunction of the implant/bone joint, leading to implant failure. Moreover, the contaminated implant can be a reservoir for infection of the surrounding tissue where microorganisms are protected. Therefore, the biofilm increases the pathogenesis of infection since that structure offers protection against host defenses and antimicrobial therapies. Additionally, the rapid emergence of bacterial strains resistant to antibiotics prompted the development of new alternative approaches to prevent and control implant-related infections. Several concepts and approaches have been developed to obtain biomaterials endowed with anti-infective properties. In this review, several anti-infective strategies based on biomaterial engineering are described and discussed in terms of design and fabrication, mechanisms of action, benefits, and drawbacks for preventing and treating orthopaedic biomaterials-related infections.

Current Advances in the Concept of Quorum Sensing-Based Prevention of Spoilage of Fish Products by Pseudomonads

Microbial spoilage of fish is attributed to quorum sensing (QS)-based activities. QS is a communication process between the cells in which microorganisms secrete and sense the specific chemicals (autoinductors, AIs) that regulate proteolysis, lipolysis, and biofilm formation. These activities change the organoleptic characteristics and reduce the safety of the products. Although the microbial community of fish is diverse and may consist of a range of bacterial strains, the deterioration of fish-based products is attributed to the growth and activity of Pseudomonas spp. This work summarizes recent advancements to assess the influence of QS mechanisms on seafood spoilage by Pseudomonas spp. The quorum sensing inhibition (QSI) in the context of fish preservation has also been discussed. Detailed recognition of this phenomenon is crucial in establishing effective strategies to prevent the premature deterioration of fish-based products.

Novel Quorum Quenching YtnP Lactonase From Bacillus paralicheniformis Reduces Pseudomonas aeruginosa Virulence and Increases Antibiotic Efficacy in vivo

Bacterial infections have become increasingly difficult to treat due to the occurrence of antibiotic-resistant strains. A promising strategy to increase the efficacy of therapy is to combine antibacterials with agents that decrease pathogen virulence via the modulation of the quorum sensing (QS). Lactonases inhibit acylated homoserine lactone (AHL)-mediated QS in Gram-negative bacteria, including the leading nosocomial pathogen Pseudomonas aeruginosa. Here we describe the characteristics of heterologously expressed YtnP lactonase from Bacillus paralicheniformis ZP1 (YtnP-ZP1) isolated from agricultural soil using the culture enrichment method. Purified YtnP-ZP1 hydrolyzed different AHLs with preference to substrates with long acyl residues as evaluated in assays with biosensors and HPLC. The enzyme showed good thermostability and activity in a wide temperature range. YtnP-ZP1 in 50 μg mL^-1 concentration reduced the amount of P. aeruginosa-produced long-chain AHLs by 85%, while it hydrolyzed 50% of short-chain AHLs. Incubation of P. aeruginosa PAO1 with YtnP-ZP1 reduced its swarming motility and elastolytic activity without bactericidal effect. YtnP-ZP1 caused the inhibition of biofilm formation and disintegration of mature biofilms in P. aeruginosa PAO1 and multiresistant clinical strain BR5H that was visualized by crystal violet staining. The treatment with YtnP-ZP1 in concentrations higher than 25 μg mL^-1 improved the survival of P. aeruginosa PAO1-infected zebrafish (Danio rerio), rescuing 80% of embryos, while in combination with tobramycin or gentamicin survival rate increased to 100%. The treatment of P. aeruginosa PAO1 biofilms on infected zebrafish tail wounds with 50 μg mL^-1 YtnP-ZP1 and 2 × MIC tobramycin led to infection clearing in 2 days. The extensive toxicity studies proved YtnP-ZP1 was non-toxic to human cells and zebrafish. In conclusion, novel YtnP-ZP1 lactonase with its effective anti-virulence activity could be used to increase the efficacy of clinically approved antibiotics in clearing both systemic and biofilm-associated P. aeruginosa infections.

Bacillus subtilis BR4 derived stigmatellin Y interferes Pqs-PqsR mediated quorum sensing system of Pseudomonas aeruginosa

Cell-to-cell communication is essentially required in bacteria for the production of multiple virulence factors and successful colonization in the host. Targeting the virulence factors production without hampering the growth of the pathogens is a potential strategy to control pathogenesis. To accomplish this, a total of 43 mangrove isolates were screened for quorum quenching (QQ) activity against Pseudomonas aeruginosa (PA), in which eight bacteria have shown antibiofilm activity without hampering the growth of the PA. Prominent QQ activity was observed in Bacillus subtilis BR4. Previously, we found that BR4 produces stigmatellin Y, a structural analogue of PQS signal of PA, which could competitively bind with PqsR receptor and inhibits the quorum sensing (QS) system of PA. Further, stigmatellin Y containing ethyl acetate extract (S-EAE) (100 µg ml^-1 ) of BR4 significantly inhibits (p < 0.001) the biofilm formation of PA. Confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM) analysis also fortified the QQ activity of BR4. Furthermore, S-EAE of BR4 (500 µg ml^-1 ) has significantly reduced the production of virulence factors, including protease, elastase, pyocyanin and extracellular polysaccharides substances. Furthermore, liquid chromatography-mass spectrometry (LC-MS)/MS analysis affirms that BR4 intercepts the PQS-mediated QS system by reducing the synthesis of as many PQS signals, including precursor molecule (243.162313 Da) of PQS signal. Thus, S-EAE of B. subtilis BR4 could be used as a promising therapeutic agent to combat QS system-mediated pathogenesis of PA. Further therapeutic potentials of stigmatellin Y to be evaluated in clinical studies for the treatment of multidrug resistant PA.

Quorum Quenching Strains Isolated from the Microbiota of Sea Anemones and Holothurians Attenuate Vibriocorallilyticus Virulence Factors and Reduce Mortality in Artemiasalina

Interference with quorum-sensing (QS) intercellular communication systems by the enzymatic disruption of N-acylhomoserine lactones (AHLs) in Gram-negative bacteria has become a promising strategy to fight bacterial infections. In this study, seven strains previously isolated from marine invertebrates and selected for their ability to degrade C6 and C10-HSL, were identified as Acinetobacter junii, Ruegeria atlantica, Microbulbifer echini, Reinheimera aquimaris, and Pseudomonas sihuiensis. AHL-degrading activity against a wide range of synthetic AHLs were identified by using an agar well diffusion assay and Agrobacterium tumefaciens NTL4 and Chromobacterium violaceum CV026 and VIR07 as biosensors. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis indicated that this activity was not due to an AHL lactonase. All the strains degraded Vibrio coralliilyticus AHLs in coculture experiments, while some strains reduced or abolished the production of virulence factors. In vivo assays showed that strains M3-111 and M3-127 reduced this pathogen’s virulence and increased the survival rate of Artemia salina up to 3-fold, indicating its potential use for biotechnological purposes. To our knowledge, this is the first study to describe AHL-degrading activities in some of these marine species. These findings highlight that the microbiota associated with marine invertebrates constitute an important underexplored source of biological valuable compounds.

Targeting Acyl Homoserine Lactones (AHLs) by the quorum quenching bacterial strains to control biofilm formation in Pseudomonas aeruginosa

Navigating novel biological strategies to mitigate bacterial biofilms have great worth to combat bacterial infections. Bacterial infections caused by the biofilm forming bacteria are 1000 times more resistant to antibiotics than the planktonic bacteria. Among the known bacterial infections, more than 70% involve biofilms which severely complicates treatment options. Biofilm formation is mainly regulated by the Quorum sensing (QS) mechanism. Interference with the QS system by the quorum quenching (QQ) enzyme is a potent strategy to mitigate biofilm. In this study, bacterial strains with QQ activity were identified and their anti-biofilm potential was investigated against the Multidrug Resistant (MDR) Pseudomonas aeruginosa. A Chromobacterium violaceum CV026 and Agrobacterium tumefaciens A136-based bioassays were used to confirm the degradation of different Acyl Homoserine Lactones (AHLs) by QQ isolates. The 16S rRNA gene sequencing of the isolated strains identified them as Bacillus cereus strain QSP03, B. subtilis strain QSP10, Pseudomonas putida strain QQ3 and P. aeruginosa strain QSP01. Biofilm mitigation potential of QQ isolates was tested against MDR P. aeruginosa and the results suggested that 50% biofilm reduction was observed by QQ3 and QSP01 strains, and around 60% reduction by QSP10 and QSP03 bacterial isolates. The presence of AHL degrading enzymes, lactonases and acylases, was confirmed by PCR based screening and sequencing of the already annotated genes aiiA, pvdQ and quiP. Altogether, these results exhibit that QQ bacterial strains or their products could be useful to control biofilm formation in P.aeruginosa.

Bacillus spp. Probiotic Strains as a Potential Tool for Limiting the Use of Antibiotics, and Improving the Growth and Health of Pigs and Chickens

The pressure to increasingly optimize the breeding of livestock monogastric animals resulted in antimicrobials often being misused in an attempt to improve growth performance and counteract diseases in these animals, leading to an increase in the problem of antibiotic resistance. To tackle this problem, the use of probiotics, also known as direct in-feed microbials (DFM), seems to be one of the most promising strategies. Among probiotics, the interest in Bacillus strains has been intensively increased in recent decades in pigs and poultry. The aim of the present review was to evaluate the effectiveness of Bacillus strains as probiotics and as a potential strategy for reducing the misuse of antibiotics in monogastric animals. Thus, the potential modes of action, and the effects on the performance and health of pigs (weaning pigs, lactation and gestation sows) and broilers are discussed. These searches yielded 131 articles (published before January 2021). The present review showed that Bacillus strains could favor growth in terms of the average daily gain (ADG) of post-weaning piglets and broilers, and reduce the incidence of post-weaning diarrhea in pigs by 30% and mortality in broilers by 6-8%. The benefits of Bacillus strains on these parameters showed results comparable to the benefit obtained by the use of antibiotics. Furthermore, the use of Bacillus strains gives promising results in enhancing the local adaptative immune response and in reducing the oxidative stress of broilers. Fewer data were available regarding the effect on sows. Discordant effects have been reported regarding the effect on body weight (BW) and feed intake while a number of studies have supported the hypothesis that feeding probiotics to sows could benefit their reproductive performance, namely the BW and ADG of the litters. Taken all the above-mentioned facts together, this review confirmed the effectiveness of Bacillus strains as probiotics in young pigs and broilers, favoring their health and contributing to a reduction in the misuse of direct in-feed antibiotics. The continuous development and research regarding probiotics will support a decrease in the misuse of antibiotics in livestock production in order to endorse a more sustainable rearing system in the near future.

Degradation of n-hexanoyl homoserine lactone with quorum quenching bacteria immobilised magnetic nanocomposite beads

N-acyl homoserine lactones (AHLs) based quorum sensing controls various phenotype expressions, including biofilm formation, hence its interruption is considered to be an ideal option for membrane biofouling control. Bead entrapped quorum quenching bacteria was reported to be an efficient approach for degradation of signal molecules in recent years. In the present study, we investigated the potential of quorum quenching (QQ) bacteria immobilised magnetic nanocomposite beads (IMN) in degradation of signalling molecule, n-hexanoyl homoserine lactone (C6-HSL). Three QQ bacteria, named Acinetobacter baumannii JYQ2, Pseudomonas nitroreducens JYQ3 and Pseudomonas JYQ4 isolated from dairy industry waste activated sludge (WAS) were immobilised in the magnetic nanocomposite (IMN) beads. The scanning electron microscopy (SEM) of the IMN beads has indicated the successful entrapment of QQ bacteria within the alginate matrix. The GC-MS analysis showed that all the QQ bacteria immobilised magnetic nanocomposite (IMN) beads degraded the signalling molecule, n-hexanoyl homoserine lactone (C6-HSL) within 72 h of incubation. The nanocomposite beads containing the QQ bacteria Pseudomonas JYQ4 showed the maximum degradation percentage of 97 ± 0.13% leaving a residual HSL of 0.7 mg/L. All the other isolates showed C6-HSL degradation percentage in the range of 87% to 95%. The data suggest the potential of C6-HSL degradation by QQ bacteria IMN beads. Hence, the study offers possibilities of controlling biofilm developed on the membrane surface during wastewater treatment processes.

In silico analysis of AhyI protein and AI-1 inhibition using N-cis-octadec-9z-enoyl-l-homoserine lactone inhibitor in Aeromonas hydrophila

AhyI is homologous to the protein LuxI and is conserved throughout bacterial species including Aeromonas hydrophila. A. hydrophila causes opportunistic infections in fish and other aquatic organisms. Furthermore, this pathogennot only poses a great risk for the aquaculture industry, but also for human public health. AhyI (expressing acylhomoserine lactone) is responsible for the biosynthesis of autoinducer-1 (AI-1), commonly referred to as a quorum sensing (QS) signaling molecule, which plays an essential role in bacterial communication. Studying protein structure is essential for understanding molecular mechanisms of pathogenicity in microbes. Here, we have deduced a predicted structure of AhyI protein and characterized its function using in silico methods to aid the development of new treatments for controlling A.hydrophila infections. In addition to modeling AhyI, an appropriate inhibitor molecule was identified via high throughput virtual screening (HTVS) using mcule drug-like databases.The AhyI-inhibitor N-cis-octadec-9Z-enoyl-l-Homoserine lactone was selected withthe best drug score. In order to understand the pocket sites (ligand binding sites) and their interaction with the selected inhibitor, docking (predicted protein binding complex) servers were used and the selected ligand was docked with the predicted AhyI protein model. Remarkably, N-cis-octadec-9Z-enoyl-l-Homoserine lactone established interfaces with the protein via16 residues (V24, R27, F28, R31, W34, V36, D45, M77, F82, T101, R102, L103, 104, V143, S145, and V168), which are involved with regulating mechanisms of inhibition. These proposed predictions suggest that this inhibitor molecule may be used as a novel drug candidate for the inhibition of auto-inducer-1 (AI-1) activity.The N-cis-octadec-9Z-enoyl-l-Homoserine lactone inhibitor molecule was studied on cultured bacteria to validate its potency against AI-1 production. At a concentration of 40 μM, optimal inhibition efficiency of AI-1 was observedin bacterial culture media.These results suggest that the inhibitor molecule N-cis-octadec-9Z-enoyl-l-Homoserine lactone is a competitive inhibitor of AI-1 biosynthesis.

Ribosomally synthesized peptides, foreground players in microbial interactions: recent developments and unanswered questions

It is currently well established that multicellular organisms live in tight association with complex communities of microorganisms including a large number of bacteria. These are immersed in complex interaction networks reflecting the relationships established between them and with host organisms; yet, little is known about the molecules and mechanisms involved in these mutual interactions. Ribosomally synthesized peptides, among which bacterial antimicrobial peptides called bacteriocins and microcins have been identified as contributing to host-microbe interplays, are either unmodified or post-translationally modified peptides. This review will unveil current knowledge on these ribosomal peptide-based natural products, their interplay with the host immune system, and their roles in microbial interactions and symbioses. It will include their major structural characteristics and post-translational modifications, the main rules of their maturation pathways, and the principal ecological functions they ensure (communication, signalization, competition), especially in symbiosis, taking select examples in various organisms. Finally, we address unanswered questions and provide a framework for deciphering big issues inspiring future directions in the field.

Quorum Quenching Enzyme (PF-1240) Capable to Degrade AHLs as a Candidate for Inhibiting Quorum Sensing in Food Spoilage Bacterium Hafnia alvei

Quorum sensing (QS) is widely present in microorganisms in marine aquatic products. Owing to the use of antibiotics, many spoilage bacteria in aquatic products are drug resistant. In order to slow down this evolutionary trend, the inhibition of spoilage phenotype of spoilage bacteria by interfering with QS has become a research hot spot in recent years. In this study, we found a new QS quenching enzyme, PF-1240; it was cloned and expressed in Pseudomonas fluorescens 08. Sequence alignment showed that its similarity with N-homoserine lactone (AHL) acylase QuiP protein of Pseudomonas fluorescens (Pf 0-1) was 78.4%. SDS-PAGE confirmed that the protein is a dimer composed of two subunits, which is similar to the structure of AHL acylases. The concentration of heterologous expression in Escherichia coli (DE3) was 26.64 μg/mL. Unlike most AHL acylases, PF-1240 can quench AHLs with different carbon chain lengths and inhibit the quorum sensing of the aquatic spoilage bacterium Hafnia alvei. It can significantly reduce the formation rate of biofilm of H. alvei to 44.4% and the yield of siderophores to 54%, inhibit the production of protease and lipase, and interfere with the motility of H. alvei. Through these corruption phenotypes, the specific application effect of PF-1240 can be further determined to provide a theoretical basis for its application in the preservation of practical aquatic products.

Resistance elicited by sub-lethal concentrations of ampicillin is partially mediated by quorum sensing in Pseudomonas aeruginosa

The rapid increase of antibiotic resistance is a serious challenge around the world. Antibiotics are present in various environments at sub-lethal concentrations, but how resistance emerges under sub-lethal conditions is not fully clear. In this study, we evolved Pseudomonas aeruginosa PAO1 under sub-lethal conditions, in the presence of either 15-30 μg/mL or 150-300 μg/mL of ampicillin. We found a ~ 5-6 fold increase in the minimum inhibitory concentration (MIC) among evolved isolates exposed to 15-30 μg/mL of ampicillin, and more than a 19-fold of increase in 150-300 μg/mL of ampicillin exposure. DNA sequencing revealed that mpl and ampD were frequently mutated in these resistant strains. We performed a transcriptome analysis of deletion mutations of mpl or ampD, compared to PAO1. Both showed a two-fold increase in expression of quorum sensing (QS) genes including lasR and rhlI/R; the heightened expression was positively correlated with the expression of the ampicillin resistance gene ampC. We queried if quorum sensing contributes to the increase in the ampicillin MIC. After adding the quorum quencher acylase I, the growth yield both decreased by roughly 50% for Δmpl in 2000 μg/mL of ampicillin and ΔampD in 4000 μg/mL of ampicillin. Addition of the QS signals into synthase mutants restored the higher MIC, but only for the rhlI/R circuit. This study highlights the involvement of QS in antibiotic resistance evolution, and shows the multifactorial contributors to the observed phenotypes.