Search Results (173)

The bacterial Quorum Sensing system refers to the recognition of signaling molecules called autoinducers produced by bacteria when a certain cell density is reached in the environment. Those cell-density-dependent autoinducers regulate and coordinate diverse functional processes, such as bioluminescence, biofilm production, sporulation, and even the expression of some virulence factors, among others. There is a wide variety of autoinducers, and for Gram-negative bacteria, the canonical autoinducers are the N-acyl-homoserine lactones (AI-1). Presently, the production of autoinducers in Leptospira has not been described; therefore, the objective of this study was to detect and identify autoinducers in this bacterial genus. We report here the expression of AI-1 in cultures ≥2.4 × 10⁸ of Leptospira meyeri. Ethyl acetate extracts of Leptospira culture supernatants were capable of activating the β-galactosidase system in the biosensor Agrobacterium tumefaciens strain NTL4. Partial identification of the leptospiral supernatant extracts was done by thin-layer chromatography (TLC), showing a similar retention factor to the synthetic standard N-Octanoyl-DL-homoserine lactone (C8-AHL) in the Leptospira supernatant extracts. In addition, infrared spectroscopy (IR) analysis showed peaks corresponding to the lactone and amide groups in both the C8-AHL standard and the Leptospira meyeri culture extracts. Moreover, High-Performance Liquid Chromatography–Mass Spectrometry (HPLC-MS/MS) confirmed the same retention time (10.7 ± 0.1 min) in both the Leptospira meyeri supernatant extracts and the C8-AHL standard. These results show that Leptospira meyeri synthesizes N-acyl homoserine lactone family autoinducers, particularly the N-Octanoyl-DL-homoserine lactone, and lay the groundwork for future research on Quorum Sensing systems in Leptospira. Full article

The aquatic pathogen Aeromonas salmonicida SRW-OG1 is responsible for substantial mortality in Epinephelus coioides and many other cultured fish species. This study investigates the contribution of trpE to the pathogenicity of A. salmonicida SRW-OG1 in E. coioides. Specifically, trpE encodes a key enzyme in tryptophan biosynthesis; however, its function in regulating virulence in A. salmonicida remains uncertain. Phenotypic assays indicate that deletion of trpE markedly impaired bacterial growth and significantly reduced multiple virulence-associated traits, including swimming motility, biofilm formation, chemotaxis, hemolytic activity, and extracellular enzyme activity. Transmission electron microscopy revealed that the ΔtrpE mutant lacked flagella, indicating that trpE is involved in flagellar formation or maintenance. In an E. coioides infection model, fish infected with ΔtrpE showed a cumulative survival rate of 48.3%, whereas those infected with the wild-type SRW-OG1 suffered 100% mortality. The ΔtrpE mutant also exhibited reduced bacterial loads in target organs (liver, head kidney, and spleen), while pretreatment with ΔtrpE provided 53.3% protection against a subsequent wild-type challenge. Transcriptomic analysis identified 616 differentially expressed genes, mainly enriched in pathways including flagellar assembly, bacterial chemotaxis, two-component systems, quorum sensing, and biofilm formation. Metabolomic analysis further showed a significant decrease in N-butyryl-L-homoserine lactone, an acyl-homoserine lactone quorum-sensing signal in the ΔtrpE mutant. These findings suggest that trpE contributes to mesophilic A. salmonicida SRW-OG1’s virulence by partially affecting quorum-sensing signal production and motility-related pathways. The attenuated phenotype and protective effect of ΔtrpE indicate its potential as a live attenuated vaccine candidate for controlling A. salmonicida infection in aquaculture. Full article

This study investigated the effects of nutritional conditions and exogenous N-acyl-homoserine lactones (AHLs) on the recovery of sodium hypochlorite (NaClO)-induced viable but non-culturable (VBNC) Vibrio parahaemolyticus. Exposure to 40 mg/L NaClO for 20 min resulted in the loss of culturability while viable cells (approximately 1.19 × 10² cells/mL) remained detectable by SYTO9/PI staining, consistent with the operational criteria for the VBNC state. Five resuscitation systems were evaluated, including tryptic soy broth (TSB) alone, heat treatment, TSB supplemented with sodium pyruvate, TSB supplemented with Tween 80, and TSB supplemented with five AHLs (C4-HSL, C6-HSL, C8-HSL, OHHL, and 3-oxo-C14-HSL). Among the tested systems, the AHL-supplemented medium showed the highest recovery efficiency, characterized by a shortened lag phase, colony characteristics and cellular morphology approaching those of normal cells, increased intracellular ATP levels, and respiratory chain activity approaching normal levels. RT-qPCR analysis showed significantly increased expression of quorum sensing- and stress response-related genes, including opaR, atpA, soxR, and katG, in the AHL-treated group compared with the TSB group. These findings suggest that AHL supplementation is associated with enhanced recovery of VBNC V. parahaemolyticus and may facilitate metabolic reactivation during this process. Full article

Quorum sensing (QS) is critically involved in mediating microbial interactions and serves as a central regulatory mechanism in bacterial pathogenesis. As an emerging countermeasure, quorum quenching (QQ) suppresses QS-regulated virulence through enzymatic or chemical disruption of signal systems. N-acyl homoserine lactone (AHL), an evolutionarily conserved QS signal, coordinates the pathogenicity of multiple plant pathogens, particularly Dickeya zeae, which causes soft rot disease in various crops and leads to substantial agricultural losses. In this study, the QQ strain Acinetobacter schindleri XJ-10 was evaluated for its capacity to degrade AHL and attenuate the pathogenicity of D. zeae EC1 in host plants. Notably, strain XJ-10 exhibited efficient AHL degradation at 0.2 mmol/L within 24 h, achieving a degradation efficiency of 98.80%. Subsequently, gas chromatography–mass spectrometry (GC-MS) analysis identified N-hexanoyl-L-homoserine lactone and propanamide as key intermediates during AHL degradation, confirming complete mineralization to CO₂ and H₂O. Based on the structural characterization of AHL and its intermediates, the metabolic pathway within strain XJ-10 was proposed. The degradation pathway initiates with the hydrolysis of the ester ring of N-hexanoyl-L-homoserine lactone, generating N-hexanoyl-L-homoserine. Subsequent carbon–nitrogen bond scission is predicted to yield N-cyclohexyl-propanamide, which is further catabolized to produce hexanamide and propanamide. Furthermore, strain XJ-10 exhibited biocontrol activity against soft rot disease affecting potato (Solanum tuberosum), radish (Raphanus sativus), and Chinese cabbage (Brassica rapa subsp. pekinensis), as its crude enzyme extract effectively reduced disease incidence and severity in planta. While strain XJ-10 showed no detectable acylase activity, it exhibited significant degradation activity against AHL, suggesting a distinct QQ mechanism. Collectively, these findings broaden the scope of QQ-based biocontrol strategies and enhance mechanistic insights into managing bacterial diseases through QS modulation. Full article

Bacteria in the human intestinal tract express more than 46 million genes, suggesting that interbacterial communication and communication with human cells are well-controlled and synchronized. Many papers have been published on quorum sensing (QS) and other forms of bacterial communication, e.g., nanotubes, nanovibrations, and electromagnetism. Autoinducers (AIs) such as AI-1 N-acyl homoserine lactones (AHLs), AI-2 boron-containing furanosyl borate diesters, AI-3 pyrazinone derivatives, a combination of AI-3/Epi (epinephrine)/NE (norepinephrine), auto-inducer peptides (AIPs), and SdiA (suppressor of division inhibition), along with their receptors, have been well-studied. However, little is known about the roles of quantum mechanics, quantum tunneling, and quantum entanglement in bacterial communication. Most proposals are hypothetical and remain conceptual frameworks supported by indirect evidence rather than validated experiments. The wave-like behavior of ions (quantum tunneling) may facilitate crossing potential energy barriers, such as cell membranes, in concert with protein channels. If this is indeed the case, ions in a quantum-tunneling state would, hypothetically, be able to pass through any part of the cell membrane and cell wall. This would, in theory, enhance biochemical reactions, interbacterial communication, and interactions with human cells. The long-range signaling ability of quanta could allow bacterial cells to maintain contact over long distances, modify their metabolic activities, and activate DNA repair systems. The wave-like behavior of subatomic particles and molecules may cause nanovibrations and generate electromagnetic fields. We argue that electrical signals generated within a biofilm by quanta may attract distant cells and enable cross-species communication. We propose a hypothetical “two-pillar” bacterial communication system, i.e., QS and quantum mechanics/tunneling/entanglement (QMTE), and discuss the advantages of combining both. Full article

Toxigenic Klebsiella oxytoca strains linked to antibiotic-associated hemorrhagic colitis produce the cytotoxins tilimycin and tilivalline, which contribute to intestinal epithelial damage during infection. Tilimycin and tilivalline are synthesized by enzymes encoded within the nonribosomal peptide synthetase (NRPS) operon, yet the regulatory mechanisms controlling operon expression remain poorly understood. SdiA, an orphan LuxR-type quorum-sensing regulator, detects exogenous N-acyl homoserine lactones (AHLs) produced by neighboring bacterial species and modulates gene expression in response to interspecies communication. Although SdiA has been implicated in virulence regulation in several enteric pathogens, its role in K. oxytoca remains unclear. This study demonstrates that SdiA positively regulates npsA, the first gene in the NRPS operon, and that this regulatory effect is enhanced in the presence of exogenous AHL. Electrophoretic mobility shift assays indicate that SdiA directly binds to the upstream regulatory region of npsA, supporting a direct interaction consistent with positive transcriptional regulation. Furthermore, deletion of sdiA significantly reduces cytotoxicity toward HeLa cells under the conditions tested. Collectively, these findings identify SdiA as a quorum-sensing-responsive activator of npsA expression and support its role in modulating cytotoxicity in toxigenic K. oxytoca strains. These results provide new insight into the influence of interspecies quorum-sensing signals on virulence-associated regulatory pathways in K. oxytoca. Full article

Quorum Quenching (QQ) is a mechanism that disrupts Quorum Sensing (QS) signaling systems, which regulate gene expression based on bacterial population density. Many fish pathogens, such as Aeromonas, utilize QS systems to regulate the expression of their virulence factors. Disrupting these systems using QQ is a promising approach for infection control in aquaculture and may provide a safe alternative to antibiotics. Therefore, identifying microorganisms with QQ activity is a relevant task in agricultural microbiology and veterinary medicine. This study examines the identification of isolates with QQ activity in the microbial community of perch and assesses their probiotic potential for the prevention of aeromonosis. In this study, we isolated 32 strains of microorganisms capable of degrading N-acylhomoserine lactone (AHL), six of which exhibited stable QQ activity. Five strains were found to belong to the genus Rhodococcus, and one strain to the genus Exiguobacterium. The selected strains were tested for the enzymatic/non-enzymatic and intra-/extracellular QQ activity, pathogen growth inhibition, biofilm formation, and hemolytic activity, as well as growth ability under various environmental conditions (salinity, pH, bile acids, and temperature). Based on the results of these tests, the R. erythropolis PFS1.20 strain was selected as the most promising probiotic. The genomic analysis revealed that the studied strain contains genes encoding QQ enzymes, siderophore biosynthesis clusters, osmoprotectors, and compounds with antimicrobial properties. These results indicate the high probiotic potential of the R. erythropolis PFS1.20. Full article

This study assessed the impact of a topical phytocomplex on the acne skin microbiota, encompassing bacterial, fungal, and phage communities. Skin samples obtained from participants exhibiting a positive response to the treatment were analyzed using high-throughput sequencing and bioinformatic approaches including taxonomic profiling, metagenome assembly, functional annotation, and phage identification. Results showed that after treatment, microbial diversity increased, reflecting a more balanced microbial composition. Cutibacterium acnes levels were reduced, particularly virulent IA1/IA2 phylotypes, whereas non-pathogenic or unclassified strains increased. Opportunistic pathogens such as Klebsiella pneumoniae were no longer detected, and beneficial genera including Psychrobacter and Dermabacter were enriched. Functional analysis showed reduced virulence- and biofilm-related pathways, alongside enhanced tryptophan metabolism, SCFA production, lipid synthesis, and riboflavin and folate biosynthesis. Fungal populations, dominated by Malassezia, became more evenly distributed, with notable post-treatment reductions in M. arunalokei, Exophiala spinifera, and Wickerhamomyces anomalus. Phage populations mirrored bacterial changes, with enrichment of Cutibacterium-associated phages post-treatment. These findings demonstrate that the phytocomplex promotes functional rebalancing of the skin microbiota by reducing pathogenic features while maintaining ecosystem stability. The inhibition of quorum sensing, potentially mediated by N-acyl-homoserine lactone acetylation, emerged from metabolic pathway annotation as a hypothetic key mechanism impairing bacterial communication and virulence associated with acne vulgaris. Full article

Botrytis cinerea, the causative agent of gray mold, is a major fungal pathogen affecting a wide range of economically important crops. To identify sustainable alternatives to chemical fungicides, this study characterized the biocontrol potential of two bacterial strains, Serratia quinivorans NFX21 and Pseudomonas thivervalensis NFX104, through genomic analysis and functional assays targeting key stages of fungal growth and plant infection. The NFX21 and NFX104 strains significantly inhibited B. cinerea mycelial growth (~35%) and strongly suppressed conidial germination with performances comparable to the reference biocontrol strain Bacillus amyloliquefaciens QST 713. In tomato detached-leaf and whole-plant pot assays, application of NFX21 and NFX104 significantly reduced gray mold incidence and lesion severity relative to nontreated infected plants (53–64%, detached leaves; 12–13%, whole-plant assays), achieving disease control levels similar to those obtained with the commercial biofungicide Serenade ASO^®. Whole-genome sequencing allowed the taxonomic assignment of the NFX strains and revealed a rich repertoire of biosynthetic gene clusters and antifungal determinants. The NFX21 genome contained genes associated with N-acyl-homoserine lactone-mediated quorum-sensing and production of lipopeptides, siderophores, and extracellular lytic enzymes. The NFX104 genome harbored clusters involved in the biosynthesis of multiple siderophores, 2,4-diacetylphloroglucinol and hydrogen cyanide. Moreover, both the NFX21 and NFX104 genomes contained additional low-homology clusters that potentially encode for novel unexplored metabolites. Collectively, these results support the translational potential of NFX21 and NFX104 as biocontrol candidates for sustainable, integrated management of gray mold caused by B. cinerea. Full article

Climate change-induced drought threatens the persistence of Araucaria araucana, an endangered and endemic conifer of the Southern Andes. Beneficial plant–microbe interactions may contribute to drought resilience. Here, we evaluated the effects of a root-endophytic bacterium with the capacity to produce N-acyl homoserine lactones (AHLs) on the growth and drought tolerance of A. araucana. For this, a root endophytic bacterium was isolated from A. araucana and identified as Erwinia billingiae. It was characterized for plant growth-promoting traits, and inoculated into A. araucana seedlings under drought conditions). The bacteria produced N-butyryl-L-homoserine lactone (C4-HSL) under control conditions and C4-HSL and N-hexanoyl-L-homoserine lactone (C6-HSL) under drought stress. The strain also produces indoleacetic acid, ammonia, siderophores and solubilizes phosphate. Under drought stress, non-inoculated seedlings showed marked reductions in shoot and root biomass, chlorophyll content, relative water content (RWC), and soluble sugars. In contrast, inoculated seedlings under drought displayed significantly higher shoot and root biomass, reaching levels comparable to those of well-watered controls. Chlorophyll content increased from 5.42 to 9.35 mg L⁻¹, and RWC increased from 62% to 71% in inoculated plants under drought conditions. Soluble sugar content increased from 25.74 to 36.34 mg g⁻¹ fresh weight following inoculation. Drought-induced oxidative stress was significantly alleviated in inoculated seedlings, with lower malondialdehyde and proline accumulation compared to non-inoculated drought-stressed plants. Antioxidant responses were modulated, indicating improved redox balance under water limitation. These results demonstrate that a root-endophytic bacterium with AHL production can enhance drought tolerance in A. araucana seedlings. This study provides novel evidence supporting the role of beneficial endophytes in microbiome-based strategies for conserving native forest species under climate change. Full article

Yersinia enterocolitica is a foodborne pathogen that forms biofilms on surfaces, enhancing its survivability and increasing bacterial resistance, which poses a significant challenge to public health. Therefore, developing effective strategies to inhibit biofilm formation is crucial. Lipoic acid (LA) is a compound with antibiofilm properties. This study investigates the effects of LA on biofilm formation by Y. enterocolitica BNCC 108930 (a standard strain from the BeNa Culture Collection). Biofilm formation, maturation, removal, and cell viability were evaluated by crystal violet staining, extracellular polysaccharide assay, Methylthiazolyldiphenyl-tetrazolium bromide assays, motility, and quorum sensing (QS) assays. The results indicate that LA interferes with the early stages of biofilm formation by compromising cell membrane integrity and reducing cellular adhesion. Furthermore, 2.5 mg/mL of LA reduced biofilm biomass (with a 48 h treatment inhibition rate of 51.46 ± 1.29%) and extracellular polysaccharide production (with a relative inhibition rate of 30.09 ± 1.8%), while significantly reducing the metabolic activity of bacteria within the biofilm (inhibition rate over 85%) compared to the untreated group. Confocal laser scanning microscopy and field emission gun scanning electron microscopy confirm that LA induces a sparse biofilm structure, reduced aggregation, and decreased biofilm thickness to 21.33 ± 2.27 μm. Motility and QS assays demonstrate that LA affects flagellar motility and the secretion of N-acyl homoserine lactones. Transcriptome analysis revealed downregulation of genes involved in the QS system and biofilm formation (e.g., lsrA, lsrC, lsrD, lsrR, and oppA), as well as upregulation of genes related to bacterial chemotaxis and flagellar assembly (e.g., RS19655, RS15590, fliE, fliJ, fliP, fliA, and fliK). These alterations suggest that LA inhibits Y. enterocolitica biofilm formation by affecting intercellular communication and flagellar motility. This study highlights the antibiofilm properties of LA, providing a theoretical basis for potential applications in microbial and biofilm control. Full article

Volatile organic compounds produced by microbes are increasingly recognized as modulators of microbial interactions and mediators of both intra- and inter-kingdom communication. This study explored the possible ecophysiological roles of nine amides from Streptomyces sp. NP10 in quorum sensing (QS) and biofilm formation in Pseudomonas aeruginosa PAO1. GC-MS profiling, synthesis, spectral validation, and co-injection experiments confirmed compound identities. Notably, N-(3-methyl-2-butenyl)acetamide is reported as a new natural product and N-(2-methylbutyl)acetamide as a new Streptomyces-produced metabolite. At subinhibitory concentrations (250 μg/mL), most of the amides enhanced P. aeruginosa biofilm formation, with N-(2-methylbutyl)acetamide, N-(3-methyl-2-butenyl)acetamide, and 2-phenylacetamide showing the strongest effects. Simultaneously, these compounds suppressed QS by reducing the production of N-acyl homoserine lactones (AHLs) and 2-alkyl-4-quinolones (AHQs). Aliphatic acetamides preferentially inhibited short-chain AHLs, while N-acetyltyramine and 2-phenylacetamide mainly affected quinolone signaling. These opposing effects on QS and biofilm are consistent with the involvement of alternative regulatory circuits. Motility assays showed biofilm stimulation was not correlated with altered swarming or twitching. Cross-species assays revealed limited QS inhibition, with only N-acetyltryptamine reducing violacein production in Chromobacterium violaceum CV026. Most of the amides were non-cytotoxic at 100 μM (10.5–20.2 μg/mL), except for 2-phenylacetamide. Overall, these amides likely serve as microbial signals influencing QS and biofilm formation, offering leads for anti-virulence strategies. Full article

N-tetradecanoyl-L-homoserine lactone (C₁₄-HSL) is a long-chain signaling molecule belonging to acyl-homoserine lactones (AHLs), which is widely present in the quorum sensing (QS) system of Gram-negative bacteria. In this study, the effects of C₁₄-HSL on chalcopyrite bioleaching mediated by Acidithiobacillus ferrooxidans (A. ferrooxidans) were investigated. After cultivating A. ferrooxidans with different energy substrates and exploring the potential mechanisms of signal molecule production, chalcopyrite was selected as the energy substrate for further study. Molecular docking analysis revealed that the high binding affinity between AHL and the receptor protein AfeR in A. ferrooxidans was beneficial for the activation of transcription by the AfeR-AHL complex, promoting their biological impact. The variations in the physicochemical parameters of pH, redox potential, and copper ions revealed that after adding C₁₄-HSL, the leaching rate of chalcopyrite increased (1.15 times during the initial 12 days). Further analysis of the mechanism of extracellular polymers formation indicated that the presence of C₁₄-HSL could promote the formation of biofilms and the adhesion of bacteria, facilitating mineral leaching rate of A. ferrooxidans. This research provides a theoretical basis for regulating the biological leaching process of chalcopyrite and metal recovery using signaling molecules, which could also be used to control environmental damage caused by acid mine/rock drainage. Full article

Unlike sucrose, sucralose is a non-cariogenic artificial sweetener, commonly included in dental care products such as chewing gums, toothpastes, and mouth rinses to enhance palatability for consumers. While its non-cariogenic action is well established, there is limited evidence regarding the potential anti-cariogenic mechanisms of sucralose. This study investigated whether sucralose interferes with QS involved in oral bacterial biofilm formation. A representative LuxR-type QS regulator, LasR, was expressed in the presence of sucralose and/or its native ligand, N-acyl homoserine lactone (AHL). The expressed protein was purified using nickel-affinity chromatography and quantified by the Bradford assay. The findings reveal that sucralose significantly inhibits AHL-dependent signaling, presumably by disrupting receptor–ligand interactions. These results provide insights into a possible molecular mechanism underlying the anti-cariogenic action of sucralose, highlighting its potential as a functional additive in oral health formulations. Full article

Plasma-activated water (PAW) is an emerging disinfectant; however, its potential as a quorum sensing inhibitor (QSI) for biofilm control remains underexplored, and its action mechanisms have not been elucidated. This study investigated the effects of PAW on biofilm formation and spoilage factors secretion in Pseudomonas fluorescens under sub-inhibitory conditions. PAW generated by treating water for 60 s (PAW-60) reduced biofilm biomass by up to 1.29 log CFU/mL after 12 h incubation. It also completely inhibited protease production (100%) and decreased siderophore production by 31.87%. N-butyryl-homoserine lactone (C₄-HSL) was identified as the dominant signaling molecule, with its production decreasing by 34.34–84.07% following PAW treatments. Meanwhile, C₄-HSL activity was significantly suppressed by 42.58–65.38%. An FTIR analysis revealed the formation of a new C=O group, indicating oxidative degradation of acyl homoserine lactones (AHLs). Exogenous C₄-HSL progressively restored the biofilm biomass, spoilage factors production, and QS-related gene expression levels, with no significant difference observed compared with the control at 0.05 µg/mL (p < 0.05). The results suggest that the inhibitory effects of PAW are primarily due to the disruption of AHLs transduction in the QS pathway. Molecular docking showed that the long-lived reactive species in PAW could bind to AHLs’ synthetic protein (FadD1) and receptor protein (LuxR) via hydrogen bonding. PAW-60 reduced the spoilage activity of P. fluorescens inoculated into fish muscle juice and extended its shelf life from 8 to 10 days during storage at 4 °C. A strong positive correlation was observed between AHLs accumulation and the spoilage process. These findings demonstrate that PAW mitigates biofilm formation and food spoilage by blocking signaling transduction, which involves suppression of AHLs production, oxidative degradation of AHLs molecules, and disruption of AHLs recognition. Full article