Quorum Sensing Research Articles

Genome-wide analysis of quorum sensing regulon in marine fish pathogen Vibrio scophthalmi.

Opportunistic fish pathogen Vibrio scophthalmi frequently infects olive flounder and turbot, which are primary marine species cultured for seafood production in Far East Asia. These infections cause substantial yield reductions and significant economic losses. Although quorum sensing (QS) genes were previously reported in V. scophthalmi, the impacts of QS on genome-wide gene expression and consequent behaviors and physiological traits have remained largely unexplored. In this study, we conducted genomic and transcriptomic analyses to uncover the global regulatory network governed by LuxRVs, a QS master regulator in V. scophthalmi. By comparing the wild-type strain and a luxRVs deletion mutant strain, we found that LuxRVs positively regulates biosynthetic genes for poly-hydroxyalkanoate (PHA) while negatively controlling genes for biofilm formation. Quantification of intracellular PHAs and biofilm biomass on borosilicate tubes confirmed these results. Gene set enrichment analyses further demonstrated that LuxRVs also governs genes related to osmoprotection and defense against reactive oxygen species. Overall, these findings indicate that LuxRVs acts as a global transcriptional regulator, controlling a wide range of physiological processes in V. scophthalmi. Targeting LuxRVs could therefore be a promising strategy for improving seafood production by disrupting diverse physiological and pathogenic traits in this fish pathogen.

Quorum sensing in Vibrio controls carbon metabolism to optimize growth in changing environmental conditions.

Bacteria sense population density via the cell-cell communication system called quorum sensing (QS). The evolution of QS and its maintenance or loss in mixed bacterial communities is highly relevant to understanding how cell-cell signaling impacts bacterial fitness and competition, particularly under varying environmental conditions such as nutrient availability. We uncovered a phenomenon in which Vibrio cells grown in minimal medium optimize expression of the methionine and tetrahydrofolate (THF) synthesis genes via QS. Strains that are genetically "locked" at high cell density grow slowly in minimal glucose media and suppressor mutants accumulate via inactivating-mutations in metF (methylenetetrahydrofolate reductase) and luxR (the master QS transcriptional regulator). In mixed cultures, QS mutant strains initially coexist with wild type, but as glucose is depleted, wild type outcompetes the QS mutants. Thus, QS regulation of methionine/THF synthesis is a fitness benefit that links nutrient availability and cell density, preventing accumulation of QS-defective mutants.

Imipenem exposure influence the expression of quorum sensing receptor sdiA in Escherichia coli.

The increasing trend of carbapenem resistance amongst Escherichia coli poses a major public health crisis and requires active surveillance of resistance mechanisms to control the threat. Quorum Sensing system plays a role in bacterial resistance to antibiotics. Quorum Sensing is a cell-cell communication system where bacteria alter their gene expression in response to specific stimuli. Here, in this study we investigated the transcriptional response of quorum sensing receptor, sdiA in E.coli under sub-inhibitory concentration of carbapenem in presence of quorum sensing signal molecules. Two E.coli isolates harbouring blaNDM were subjected to treatment with 10% SDS for 20 consecutive days of which blaNDM encoding plasmid was successfully eliminated from one isolate. Both the wild type and the cured mutant were then allowed to grow under eight different inducing conditions and the transcriptional response of sdiA gene was studied by quantitative real time PCR method. We found different response levels of sdiA in wild type and cured mutant under exogenous AHL and imipenem and when co-cultured with P.aeruginosa under imipenem stress. This study highlighted that sub-inhibitory concentration of imipenem in combination with AHL is acting as signal to SdiA, a quorum sensing receptor in E.coli.

Control of membrane biofouling in MBR for wastewater treatment by biohybrid membrane with superhydrophilic self-QQ function

Quorum quenching (QQ) is an effective method for controlling MBR (membrane bioreactor) membrane biofouling by regulating the release of autoinducer during the quorum sensing (QS) process. However, the addition of QQ bacteria solution or QQ carriers inevitably leads to unpredictable effects on MBR microbial systems and operational efficiency (for example, reduced stability of nitrification and denitrification processes, reduced biodegradation efficiency and unbalanced biofilm formation etc.). Here, we present a biohybrid membrane called ES-BM (electrospinning-biohybrid membrane), which features a unique pore size structure consisting of electrospun superhydrophilic nanofiber sheaths, a self-QQ layer (active QQ bacteria are immobilized within the interlayer structure of this biohybrid membrane to inhibit the QS process of biofilm-forming associated bacteria at the source surface where membrane biofouling occurs), and a basement filter layer, which maintain the activity of QQ bacteria for an extended period. The ES-BM extends operational cycles up to 21 days at a constant flux of 24 L/m²/h, which is three times longer than conventional MBR systems. The membrane exhibits exceptional hydrophilicity (water contact angle of approximately 0° within 2 seconds) and high tensile strength (Young’s modulus of 135 MPa). Long-term bioactivity tests confirm the stability and recyclability of the ES-BM. Additionally, microbial community analysis suggests that the biohybrid membrane suppresses the growth of biofilm-related bacteria without significantly affecting the indigenous microbial population, further enhancing system performance. This work demonstrates the potential of ES-BM for improving MBR biofouling resistance and presents insights into scalable electrospinning fabrication techniques.

A metagenomic catalogue of the ruminant gut archaeome

While the ruminant gut archaeome regulates the gut microbiota and hydrogen balance, it is also a major producer of the greenhouse gas methane. However, ruminant gut archaeome diversity within the gastrointestinal tract (GIT) of ruminant animals worldwide remains largely underexplored. Here, we construct a catalogue of 998 unique archaeal genomes recovered from the GITs of ruminants, utilizing 2270 metagenomic samples across 10 different ruminant species. Most of the archaeal genomes (669/998 = 67.03%) belong to Methanobacteriaceae and Methanomethylophilaceae (198/998 = 19.84%). We recover 47/279 previously undescribed archaeal genomes at the strain level with completeness of >80% and contamination of <5%. We also investigate the archaeal gut biogeography across various ruminants and demonstrate that archaeal compositional similarities vary significantly by breed and gut location. The catalogue contains 42,691 protein clusters, and the clustering and methanogenic pathway analysis reveal strain- and host-specific dependencies among ruminant animals. We also find that archaea potentially carry antibiotic and metal resistance genes, mobile genetic elements, virulence factors, quorum sensors, and complex archaeal viromes. Overall, this catalogue is a substantial repository for ruminant archaeal recourses, providing potential for advancing our understanding of archaeal ecology and discovering strategies to regulate methane production in ruminants.

Insights into molecular mechanisms of phytochemicals in quorum sensing modulation for bacterial biofilm control.

Biofilm formation is a common mechanism by which bacteria undergo phenotypic changes to adapt to environmental stressors. The formation of biofilms has a detrimental impact in clinical settings by contributing to chronic infections and promoting antibiotic resistance. Delving into the molecular mechanisms, the quorum sensing (QS) system involves the release of chemical signals for bacterial cell-to-cell communication, which activates and regulates the expression of various genes and virulence factors, including those related to biofilm formation. Accordingly, the QS system becomes a potential target for combating biofilm-associated concerns. Natural products derived from plants have a long history of treating infectious diseases in humans due to their antimicrobial properties, making them valuable resources for screening anti-biofilm agents. This review aims to discover the mechanisms by which phytochemical agents inhibit QS, potentially offering promising new therapies for treating biofilm-associated infections. By targeting the QS system, these phytochemical agents can prevent bacterial aggregation and biofilm formation while also diminishing other bacterial virulence factors. Additionally, it is important to focus on the advancement of techniques and experiments to investigate their molecular mechanisms. A thorough understanding of these mechanisms may encourage further studies to evaluate the safety and efficacy of phytochemical agents used alone or in combination with other strategies.

Quorum sensing orchestrates parallel cell death pathways in Vibrio cholerae via Type 6 secretion-dependent and -independent mechanisms

Quorum sensing (QS) is a cell-to-cell communication process that enables bacteria to coordinate group behaviors. In Vibrio cholerae colonies, a program of spatial-temporal cell death is among the QS-controlled traits. Cell death occurs in two phases, first along the colony rim, and subsequently, at the colony center. Both cell death phases are driven by the type 6 secretion system (T6SS). Here, we show that HapR, the master QS regulator, does not control t6ss gene expression nor T6SS-mediated killing activity. Nonetheless, a ΔhapR strain displays no cell death at the colony rim. RNA-Sequencing (RNA-Seq) analyses reveal that HapR activates expression of an operon containing four genes of unknown function, vca0646-0649. Epistasis and overexpression studies show that two of the genes, vca0646 and vca0647, are required to drive cell death in both a ΔhapR and a ΔhapR Δt6ss strain. Thus, vca0646-0649 are regulated by HapR but act independently of the T6SS machinery to cause cell death, suggesting that a second, parallel pathway to cell death exists in V. cholerae.

Targeting Bacterial Communication: Evaluating Phytochemicals as LuxS Inhibitors to Disrupt Quorum Sensing

Bacterial quorum sensing (QS) is a critical communication process that regulates gene expression in response to population density, influencing activities such as biofilm formation, virulence, and antibiotic resistance. This study investigates the inhibitory effects of five phytochemicals—apigenin, carnosol, chlorogenic acid, quercetin, and rosmarinic acid—on the S-ribosylhomocysteinase (LuxS) enzyme, a key player in AI-2 signaling across both Gram-positive and Gram-negative bacteria. Using molecular docking studies, we identified that these phytochemicals interact with the LuxS enzyme, with apigenin, carnosol, chlorogenic acid, and rosmarinic acid binding within the substrate-binding pocket and exhibiting binding scores below −7.0 kcal/mol. Subsequent in vitro assays demonstrated that these compounds inhibited AI-2 signaling and biofilm formation in Escherichia coli MG1655 in a concentration-dependent manner. Notably, carnosol and chlorogenic acid showed the most potent effects, with IC50 values of approximately 60 μM. These findings suggest that these phytochemicals may serve as potential QS inhibitors, providing a foundation for developing new anti-pathogenic agents to combat bacterial infections without promoting antibiotic resistance. Further studies are warranted to explore the therapeutic applications of these compounds in both clinical and agricultural settings.

Autoinducer-2 relieves soil stress-induced dormancy of Bacillus velezensis by modulating sporulation signaling

The collective behavior of bacteria is regulated by quorum sensing (QS). Autoinducer-2 (AI-2) is a common QS signal that regulates the behavior of both Gram-positive and Gram-negative bacteria. Despite the plethora of processes described to be influenced by AI-2 in diverse Gram-negative bacteria, the AI-2-regulated processes in Bacilli are relatively unexplored. Here, we describe a novel function for AI-2 in Bacillus velezensis SQR9 related to the sporulation. AI-2 inhibited the initiation of sporulation through the phosphatase RapC and the DNA binding regulator ComA. Using biochemistry experiments, we demonstrated that AI-2 interacts with RapC to stimulate its binding to ComA, which leads to an inactive ComA and subsequently a sporulation inhibition. The AI-2 molecule could be shared across species for inhibiting Bacillus sporulation and it also plays the same role in different soil conditions. Our study revealed a novel function and regulatory mechanism of AI-2 in inhibiting sporulation in Bacilli.

Unveiling Quorum Sensing Mechanisms: Computational Docking and Dynamics of Bacterial Receptors and Ligands

The bacterial cell-to-cell communication mechanism known as quorum sensing (QS) uses chemical cues called autoinducers (AIs) to control several processes, including pathogenicity, antibiotic resistance, and biofilm formation. This study investigates the QS receptor-ligand interactions and QS compatibility within and between bacterial species using computational molecular docking. Receptor proteins including LuxS, LuxP, AgrC, LuxN, SdiA, LasR, esaR, YenR, LamC, PlcR, and TraR were docked with their respective AIs (AHL, AI-1, AI-2, AIP1, LamD, PapR7) in both biofilm and non-biofilm producing bacteria. Our findings indicate that QS receptors exhibit high affinity for their cognate ligands, with binding affinities ≥ -4.5 Kcal/mol. Additionally, Zinc Pharmar-derived similar chemical structures demonstrated binding affinities ≥ -5.3 Kcal/mol. Density Functional Theory (DFT) analysis revealed AI-2 as the most reactive autoinducer. Molecular Dynamics (MD) simulations confirmed the stability of LasR-AHL and LuxP-AI-2 complexes. These insights pave the way for further in vitro and in vivo investigations of QS mechanisms.

Regulation of the RCK1 gene on the oxidative tolerance of Saccharomyces cerevisiae

Our previous work indicated that the quorum sensing (QS) effect could regulate the oxidative tolerance of Saccharomyces cerevisiae, and QS may impact oxidative and antioxidative metabolisms of S. cerevisiae by regulating the RCK1 gene. Therefore, this work proposed a reasonable logic that RCK1 could play roles in regulating the oxidative and antioxidative metabolisms of yeast cells. The results presented here suggested that the overexpression of RCK1 has a regulatory effect on the reduction of ROS level and the promotion of oxidative tolerance of S. cerevisiae. The overexpression of RCK1 promoted the ROS generation through activating the MAPK pathway; on the other hand, RCK1-regulated antioxidative metabolism played a more significant role to realize lower ROS level and higher oxidative tolerance of S288c-RCK1 and ΔARO80-RCK1 strains. To improve the fermentation performance of yeast while circumventing metabolic burden, a recombinant strain with over time-controlled overexpression of the RCK1 gene (i.e., S288c'-RCK1 strain) derived from S288c strain was successfully constructed to achieve artificial regulation of yeast oxidative tolerance. Transcriptomics analysis was further performed on both S. cerevisiae wild-type and S288c'-RCK1 strains to identify differentially expressed genes and analyze their functional pathway classification. This work is instructive for artificially modulating the oxidative tolerance of strains to enhance the fermentation performance of yeast.

Harnessing anti-infective efficacy of Cinnamomum verum in synergy with β-lactam and fluoroquinolones drugs to combat virulence and biofilms of Pseudomonas aeruginosa PAO1

Multidrug resistance (MDR) Gram-negative bacteria are increasingly resistant to multiple antibiotics, posing a serious challenge to infection control and treatment. Combining plant-derived bioactives with antibiotics offers a promising approach to overcome the challenges posed by MDR pathogens like Pseudomonas aeruginosa. This study investigated the synergistic effects of Cinnamomum verum with beta-lactam and fluoroquinolones against P. aeruginosa PAO1. The ethyl acetate fraction of C. verum (CVEF) was obtained through fractionation in organic solvents with progressively higher polarity. The interaction of CVEF with selected antibiotics was assessed by checkerboard synergy assay. The effects of synergistic combinations on pyocyanin, pyoverdine, protease, EPS production, and biofilm development were measured using spectroscopic assays. CVEF combined with cefepime, ceftazidime, and levofloxacin significantly enhanced antibacterial efficacy with FICIs between 0.156 to 0.5. The most active combinations i.e., CVEF-cefepime and CVEF-ceftazidime inhibited viable cell count of growth by 3.6 and 4.2 log10 CFU/ml respectively. The combination also inhibited virulence factors (>75%) and biofilms (>80%) at lower 1/2×FICs. The viable count of biofilm cells was also reduced from 6.4 to 3.3 and 3.6 log10 CFU/ml. Membrane permeability was decreased by 60.34% and biofilm cell viability by 22.53-38.44%. Key phytochemicals analyzed by GC/MS and LC/MS/MS, include cinnamaldehyde, trans-chlorogenic acid, quercetin, and quercetin 3'-O-glucuronide. In molecular docking investigations, quercetin 3'-O-glucuronide had the highest binding affinity with quorum sensing (QS) and biofilm-associated protein. The findings suggest CVEF, in combination with antibiotics, effectively targets resistance phenotypes of P. aeruginosa, impairing growth, virulence, and biofilms. This supports further research into natural compounds alongside antibiotics to treat drug-resistant infections.

Effects of different quorum sensing signal molecules on alleviation of ammonia inhibition during biomethanation

Anaerobic digestion (AD) is a promising technology for achieving both organic wastes treatment and energy recovery. However, challenges such as ammonia inhibition still remain. Quorum sensing (QS) system is relevant with the regulation of microbial community behaviors by releasing and sensing signal molecules, which could improve methane production during AD process. Therefore, the current study explored the effects of different quorum sensing signal molecules on alleviation of ammonia inhibition. The results showed that both secretion of N-butyryl-DL-homoserine lactone (C4-HSL) and N-(β-ketocaproyl)-DL-homoserine lactone (3OC6-HSL) could be inhibited by high ammonia stress while stimulation of N-hexanoyl-L-homoserine lactone (C6-HSL) and N-octanoyl-DL-homoserine lactone (C8-HSL) secretion might be triggered by ammonia toxicity. Moreover, the alleviation of ammonia inhibition could be achieved by both introducing 3OC6-HSL (0.5 μM) and combination of 3OC6-HSL (0.1 μM) and biochar (4 g/L). Exogenous 3OC6-HSL could regulate microbial social behaviors and enhance the secretion of extracellular polymeric substances (EPS) to promote anaerobic digestion. In addition, the mitigation of ammonia inhibition through exogenous 3OC6-HSL and biochar were confirmed by microbial community changes (Methanobacterium, Propionicicella and Petrimonas). Critical enzymes involved in both acidification and methanogenic steps were enhanced after adding the combination of 3OC6-HSL and biochar. The combination of low levels of 3OC6-HSL and biochar could promote both direct interspecies electron transfer (DIET) process and communication between different anaerobic microorganisms to mitigate ammonia inhibition. The current study will provide primary insights for conquering ammonia inhibition during biomethanation.

Tracing the path of Quorum sensing molecules in cystic fibrosis mucus in a biomimetic in vitro permeability platform

P. aeruginosa employs specific quorum sensing (QS) mechanisms to orchestrate biofilm formation, enhancing resistance to host defences. In physiological conditions, QS molecules permeate the lung environment and cellular membrane to reach the cytoplasmic Aryl Hydrocarbon Receptor (AhR) that is pivotal for activating the immune response against infection. In pathological conditions like cystic fibrosis (CF) this interkingdom communication is altered, favouring P. aeruginosa persistence and chronic infection. Here, we aim to investigate the molecular journey of QS molecules from CF-like environments to the cytoplasm by quantifying via HPLC-MS the permeability of selected QS molecules (quinolones, lactones, and phenazines) through in vitro models of the two main biological lung barriers: CF-mucus and cellular membrane. While QS molecules not activating AhR exhibit intermediate permeability through the cellular membrane model (PAMPA) (1.0–4.0 × 10−6 cm/s), the AhR-activating molecule (pyocyanin) shows significantly higher permeability (8.6 ± 1.4 × 10−6 cm/s). Importantly, combining the CF mucus model with PAMPA induces a 50% decrease in pyocyanin permeability, indicating a strong mucus-shielding effect with pathological implications in infection eradication. This study underscores the importance of quantitatively describing the AhR-active bacterial molecules, even in vitro, to offer new perspectives for understanding P. aeruginosa virulence mechanisms and for proposing new antibacterial therapeutic approaches.

New 24-Membered Macrolactines from an Arctic Bacterium Bacillus amyloliquefaciens SCSIO 41392 and Their Anti-Pathogenicity Evaluation

Three new 24-membered macrolactines, amylomacrolactines A–C (1–3), along with two known compounds 4 and 5, were isolated from the Arctic bacteria Bacillus amyloliquefaciens SCSIO 41392. The configurations of 1–3 were assigned by a combination of coupling constants, NOESY, and analysis of MM2-optimized conformation, as well as by comparison with reports in the literature. Compounds 1 and 2 showed quorum sensing (QS) inhibitory activities against the Pseudomonas aeruginosa (P. aeruginosa) PQS system and suppressed PQS-regulated virulence factor pyocyanin synthesis. In addition, compounds 3–5 affected the production of another essential virulence factor, siderophore of pyoverdine (PVD), in P. aeruginosa. More importantly, compound 5 showed an anti-biofilm activity against P. aeruginosa. Altogether, the isolated compounds displayed multiple bacterial virulence inhibition activities, which is worthy of further exploration for novel analogues in antimicrobial drug development.

Synergistic effect of antibiotics, α-linolenic acid and solvent type against Staphylococcus aureus biofilm formation.

A promising approach to the treatment of bacterial infections involves inhibiting the quorum sensing (QS) mechanism to prevent the formation and growth of bacterial biofilm. While antibiotics are used to kill remaining bacteria, QS inhibitors (QSIs) allow for antibiotic doses to be reduced. This study focuses on evaluating the synergy between gentamicin sulphate (GEN), tobramycin (TOB), or azithromycin (AZM) with linolenic acid (LNA) against the formation of an early Staphylococcus aureus biofilm. Minimum biofilm inhibitory concentration (MBIC) was determined using the resazurin reduction assay for all antibiotics and LNA. The reduction of biofilm mass was assessed using the crystal violet (CV) assay. We have also evaluated the effect of dimethyl sulfoxide with TWEEN (DMSO_T) on early biofilm formation. Synergy was determined by metabolic activity assay and fractional biofilm inhibitory concentration (FBIC). DMSO_T at a concentration of 1% enhanced early biofilm formation, but also decreased the doses of antibiotic needed to reduce the biofilm by up to 8 times. Adding LNA at a concentration of 32µg/ml or 64µg/ml allowed up to a 32-fold reduction of antibiotic doses for GEN and TOB and a 4-fold reduction for AZM. LNA's use in combination with various antibiotics could reduce their doses and help fight drug-resistant bacteria in the biofilm.

Novel Polyphenolic Hybrids Modulate Quorum Sensing Regulated Virulence in Pseudomonas aeruginosa

AbstractNaturally occurring substituted benzoic acids, known for their exceptional biological activity against Pseudomonas aeruginosa, were reacted with various aldehydes, aniline, and tert‐butyl isocyanide at 25 °C to give the desired hybrids with good to excellent yield in the range of 60–85 % and well characterized by 1H NMR, 13C NMR, HRMS, IR, and HPLC analysis. Molecular docking and simulation studies of compounds were conducted which predicted a high affinity towards quorum‐sensing (QS) receptors of P. aeruginosa. The polyphenolic hybrids were first screened for anti‐QS activity using the Agrobacterium tumefaciens NTL4 biosensor strain, followed by examining the antivirulence potential of selected hybrids against P. aeruginosa PAO1 in vitro. The highest degree of AHL (acyl homoserine lactone) inhibition in PAO1 was observed with the compound having a maximum number of phenolic groups. The hybrids in this investigation were also found to be non‐cytotoxic (biocompatible) towards HEK cells and may be further tested for their therapeutic efficacy against P. aeruginosa infections in vivo. It has been observed that the anti‐QS activity is directly proportional to the number of hydroxyl groups on the aromatic ring and one of the major contributing factors can be their chelating capacity as depicted by CAS shuttle assay.

Identification and characterization of LuxR solo homolog PplR in pathogenic Pseudomonas plecoglossicida NB2011.

Pseudomonas plecoglossicida is a causative agent of visceral granulomas in large yellow croaker (Larimichthys crocea). Quorum sensing (QS) is widely involved in imparting virulence to pathogenic bacteria; however, it has not been studied in P. plecoglossicida. In this study, we annotated a LuxR family transcriptional regulator in P. plecoglossicida NB2011 and designated as PplR. We aligned the protein sequence by BlastP and Clustal X2, monitored the N-acyl-homoserine lactone (AHL) signal production through cross-feeding bioassay and HC-MS/MS; investigated exogenous AHL signal binding by recombinant expression and thin layer chromatography; constructed a deletion mutant of the target gene by method of double homologous recombination; sequenced the transcript RNA and analyzed the data; additionally, characterized phenotypes of wild type and mutant strain. The LuxR homolog PplR was found to share high similarity with PpoR-the LuxR solo of Pseudomonas putida-without a cognate LuxI. The wild-type strain did not produce any AHL signals and the recombinant LuxR protein was found to bind C6-L-homoserine lactone (C6-HSL), C8-HSL, 3-oxo-C10-HSL, and 3-oxo-C12-HSL. RNA-seq analysis indicated 84 differentially expressed genes-5 upregulated and 79 downregulated-mainly enriched in gene ontology terms, such as flagella-dependent motility, integral component of membrane, DNA binding and transcription, and metal ion binding, suggesting that PplR is a master transcription regulator. The mutant strain showed attenuated biofilm-forming ability and stress resistance, and the data support a role for PplR in the regulation of these traits in P. plecoglossicida NB2011 independent of the presence of AHL signals. This is the first study to provide QS-related information on P. plecoglossicida.

Understanding rhizospheric microbial dynamics in gladiolus corms through quorum sensing and quorum quenching for disease control and growth promotion

Gladiolus, a widely cultivated cut flower known for its aesthetically pleasing multicoloured spikes, has earned significant commercial popularity. A comprehensive understanding of the rhizosphere bacterial community associated with gladiolus is imperative for revealing its potential benefits. Molecular characterization is considered an effective method to gain insights into the structural and functional aspects of microbial populations. The soil characteristics and bacterial communities in the rhizosphere are typically influenced by quorum sensing (QS) and quorum quenching (QQ) mechanisms. This study aims to explore the niceties and diversity of rhizospheric bacterial populations linked with gladiolus corms, with a specific focus on understanding the dynamics of QS and QQ mechanisms in their complex interactions. The isolation of bacterial strains was achieved through the serial dilution method on nutrient agar (NA) media. The identification of the isolates was accomplished by amplifying 16 S rRNA gene sequences via polymerase chain reaction (PCR) via the use of universal primers. Sequence analysis was conducted via BLAST on the National Center for Biotechnology Information (NCBI) database. The characteristics of the isolated bacteria were elucidated via biosensors. This study identified three QS strains and five QQ strains. A consortium of quenchers was formulated utilizing five strains that demonstrated efficacy in mitigating the impact of disease on gladiolus and fostering growth. Among the three treatments—Scale, Descale, and Descale and Cut Half (DSC)—the DSC treatment emerged as the most effective. This treatment exhibited a broader range of variation in biological parameters over time, aligning with prevailing trends in the local market.

Bacillus quorum quenching shapes the citrus mycobiome through interkingdom signaling

Microbiomes are sustained through infinite yet mutually interacting microbial communities, with bacteria and fungi serving as the major constituents. In recent times, microbial interventions have become popular for microbiome manipulation to achieve sustainable goals. Whether and how the introduced biocontrol agent drives fungal microbial assemblages (mycobiome) and the role of interkingdom signaling in shaping the microbiome structure and function remain poorly understood. Here, we implemented wild-type (WT) Bacillus subtilis L1–21 and its quorum quenching (QQ) mutants (L1–21Δytnp, L1–21Δyxel) individually and as consortia to explore the enrichment patterns of key mycobiome members in Huanglongbing (HLB) infected citrus compartments including leaf endosphere, root endosphere, and rhizosphere soil. The application of WT and its QQ mutants produced differential mycobiome enrichment across citrus compartments. Our findings reveal that application of WT B. subtilis enriched beneficial fungi such as Trichoderma (15.82 %) in leaf endosphere. In contrast, pathogenic fungi Fusarium (47.5 %) and Gibberella (0.47 %) involved in citrus root decline were adundant in the L1–21Δytnp treated root endosphere while Nigrospora (11 %) was predominant in L1–21Δyxel treated leaf endosphere, affirming the role of bacterial quorum sensing (QS) molecules in shaping the fungal community composition. In general, based on the fungal functional prediction, fungal pathogens were highly abundant in mutant-treated plants, particularly in leaf endosphere (L1–21Δytnp: 25 %; L1–21Δyxel: 36.35 %) compared to WT (20.93 %). Additionally, some fungal members exhibited strong compartment specificity and both mutants induced distinct mycobiome shifts in rhizosphere soil, leaf, and root endopshere. In conclusion, B. subtilis QQ modifies bacterial QS networks facilitating beneficial fungi to establish, while loss of QQ leads to enrichment of pathogenic fungal groups. Our study provides a direct link of perception and regulation of mycobiome through bacterial-based QS and QQ system, and its association with disease outcomes.