Quorum sensing for population-level control of bacteria and potential therapeutic applications

Rhizobial, passenger nodule endophytes and phyllosphere bacteria in combination with acyl homoserine lactones enhances the growth and yield of groundnut

Quorum sensing (QS) mechanisms play an essential role in mediating several signals and plant-bacteria interactions, promoting plant growth. This study demonstrated production of multiple Homoserine lactone (HSL) molecules like C6 HSL, C7 HSL, C8 HSL, 3-Hydroxy-C8-HSL and 3-oxo-C14 HSL in rhizobial and passenger endophytes and phyllospheric bacteria which regulated production of plant growth promoting traits viz., indole acetic acid and exo-polysaccharide production, biofilm formation, and motility. Quorum quenching (QQ) molecules like salicylic acid, gallic acid, and disalicylic acid impaired these traits, but exogenous addition of QS molecules (C7HSL and 3-oxo-C14 HSL) restored these inhibitory effects of QQ compounds. The pot culture experiment revealed that the treatment involving Methylobacterium populi TMV7-4 or Enterobacter cloacae S23 with salicylic acid, C7HSL and 3-oxo-C14 HSL significantly enhanced plant growth including root length, nodulation, pod formation, soil available nutrients and plant nutrients uptake. In future field validation is required for the use of QS molecules in improving groundnut production.

Mining and validating quorum sensing interference molecules from food-derived compounds for Salmonella Typhimurium

Food-derived compounds represent a promising reservoir for developing novel therapeutic agents against pathogenic infections such as Salmonella Typhimurium. In this study, we integrated computational biology with experimental validation to identify and characterize quorum sensing interference molecules (QSIMs) from food-derived compounds. Through structure-based virtual screening of more than 8000 compounds in the FooDB database, we identified the potential candidates (such as skatole, 2-aminoquinoline, tricarballylic acid, and L-3-phenyllactic acid) demonstrating high affinity binding to the LsrB receptor, as validated by surface plasmon resonance analysis. We further evaluated the performances of the aforementioned QSIMs on strain growth, biofilm formation, and motility. Furthermore, we have also deciphered the corresponding mechanisms and verified the effectiveness of the obtained QSIMs. Finally, we discussed the opportunities and challenges in the development of food-derived QSIMs for weakening virulence, reducing infection and relieving drug resistance of some other pathogens.

Analysing the integrated quorum sensing system its potential role in Pseudomonas aeruginosa pathogenesis

Since its discovery, Quorum Sensing (QS), a form of bacterial communication, has been the focus of numerous studies aimed at unravelling the mechanisms behind this intricate process. Bacterial QS relies on releasing low molecular weight signals known as autoinducers (AIs). When these AIs reach a threshold concentration, they activate coordinated genetic expression of pathogenic and bacterial survival mechanisms. Pseudomonas aeruginosa's QS has been extensively studied due to its incidence and clinical significance in a wide range of human infections. Several decades ago, three QS systems, named Las, Rhl, and Pqs, were identified and have since then become the focus of numerous research studies and the target of innovative diagnostic and therapeutic strategies. However, a fourth QS-related system was more recently proposed that it has been the subject of debate. Named "integrated quorum sensing" (Iqs), interconnects the previously mentioned systems with the phosphate stress response. The associated AI has been identified as 2-(2-hydroxyphenyl)-thiazole-4-carbaldehyde, also known as IQS. This discovery has sparked a controversial discussion about its biosynthetic origin and whether it truly functions as an intercellular communication system. In this review, we critically discuss the different hypotheses, and its biological relevance while presenting key findings of the Iqs system.

4-Hydroxyboesenbergin B of Alpinia japonica protected gastrointestinal tract by inhibiting vancomycin-resistant enterococcus and balancing intestinal microbiota

ETHNOPHARMACOLOGICAL RELEVANCE

Alpinia japonica, a traditional herb utilized in Miao medicine in southwestern China, has been employed to alleviate symptoms such as stomachache, diarrhea, and abdominal pain, some of these symptoms may be associated with bacterial infections of the gastrointestinal tract.

AIM OF THE STUDY

To explore antimicrobial compounds related to traditional uses of A. japonica and its potential pathway in vitro and in vivo.

MATERIALS AND METHODS

Bioactive components of A. japonica were isolated by bioguide separation method. The antibacterial bioactivity of 4-hydroxyboesenbergin B (4-HB) was evaluated by time-kill curve and drug resistance induction. The pathway of 4-HB against VRE was investigated through network pharmacological analysis and validated by in vitro experiments and RT-qPCR assays. Moreover, a mouse gastrointestinal tract model was established to validate the antibacterial bioactivity of 4-HB in vivo.

RESULTS

4-HB from A. japonica inhibited VRE (MIC = 16 μg/mL), rapidly killed the bacteria within 4 h at the 4 MIC concentration and exhibited low susceptibility to drug resistance. 4-HB specifically targeted VRE biofilms by down-regulating the expression of AtlA, SgrA, GelE, and Ace. As a result, 4-HB diminished the adhesion and aggregation ability of VRE, reduced the extracellular matrix content, disrupted biofilm structure and morphology, thereby reducing VRE resistance and virulence. Additionally, 4-HB significantly reduced VRE colonization, enhanced intestinal microbiota diversity, and promoted the restoration of intestinal microbiota balance in vivo. Notably, 4-HB enhanced the abundance of beneficial bacteria genera, such as Lactobacillus and Limosilactobacillus.

CONCLUSIONS

4-HB has a significant ability to destroy VRE biofilms and balance intestinal microbiota, which might be responsible for the traditional use of A. japonica partly.

Quorum sensing of Bifidobacteria: Research and progress

Quorum sensing (QS) is a common method of communication among bacteria. While previous studies have discovered the mechanisms of QS in a variety of pathogenic bacteria, relatively little research has focused on probiotics, such as Bifidobacteria. Recent studies have detected QS signalling molecules in Bifidobacteria, but it remains unclear whether the probiotic properties of Bifidobacteria are mediated by QS. This review aims to provide an overview of the QS system in Bifidobacteria and its role in promoting the secretion of metabolites such as extracellular vesicles and biofilms. The review further examines the inhibition of virulence gene expression by Bifidobacteria QS through the luxS/AI-2 system, as well as its role in promoting host-microbial interactions. Understanding the QS mechanisms of Bifidobacteria can reveal beneficial interactions with hosts, which may facilitate the control of bacterial infections, including therapeutic strategies for intestinal diseases. This knowledge can also help improve gut health, thereby addressing the opportunities and challenges of enhancing the body's nutritional status.

Engineering the D-lactic acid responsive promoter/repressor system as dynamic metabolic engineering tool in Lactobacillus delbrueckii subsp. bulgaricus for controlled D-lactic acid biosynthesis

Dynamic metabolic engineering integrates synthetic logic circuits into cellular systems, optimizing metabolic fluxes and augmenting biosynthesis of target metabolites. This study evaluated a D-lactic acid (DLA)-responsive promoter-repressor system from Pseudomonas fluorescens A506, re-engineered for heightened sensitivity and functional efficacy in Lactobacillus delbrueckii subsp. bulgaricus VI104. The codon-optimized regulatory architecture exhibited peak performance at DLA inducer concentration range of 60-100 mM, validated by fluorometry and microscopy. As an application, overexpression of D-lactate dehydrogenase (dldh) downstream of the engineered promoter repressor system enabled finely tuned modulation of DLA biosynthesis, autonomously regulating the transition between growth and production phases, thereby attenuating overall metabolic load. Cross-species compatibility was confirmed by excising regulatory elements from the promoter-repressor system and functionally assessing them in recombinant L. bulgaricus. Molecular docking elucidated critical noncovalent interactions between D-LldR repressor and operator nucleotide sequence in absence of inducer DLA. The engineered promoter construct with high efficiency effectively elevated DLA biosynthesis by 2.15-folds and expanded the overall fermentation time relative to constitutive systems, attaining maximum DLA titre of 9.02 g L⁻1 in bioreactor setup. These results substantially broaden the molecular cloning toolkit available for L. bulgaricus, fostering potential future applications in biotherapeutics and probiotics.

A feasible regulation strategy for conjugation of antibiotic resistance genes based on different bacterial quorum sensing inhibition methods

The dissemination of antibiotic resistance genes (ARGs) poses global environmental issues, and plasmid-mediated conjugation contributes substantially to the spread of ARGs. Quorum sensing (QS), an important cell-cell communication system that coordinates group behaviors, has potential as a feasible regulation pathway to inhibit the conjugation process. We examined the promoting effects of QS signal on conjugation, and this study is the first to report that QS inhibitors 2(3H)-benzofuranone and acylase I effectively repressed conjugation frequency of RP4 plasmid to 0.32- and 0.13-fold compared with the control respectively. The investigation of underlying mechanisms of QS inhibitors revealed a significant decrease in cellular contact and the formation of transfer channels. The downregulation of sdiA gene regulating the expression of QS signal receptor contribute to conjugation inhibition. Importantly, the expression of genes related to the formation of conjugative pili, which plays a role in plasmid mating bridge formation was downregulated, indicating QS inhibitors affect conjugation mainly through regulation of the mating pair formation system. Furthermore, 2(3H)-benzofuranone and acylase I achieved 84.07% and 66.05% inhibitory effect on plasmid spread in activated sludge reactors. Collectively, our findings demonstrate the feasibility of using different bacteria quorum quenching methods to control the spread of ARGs.

Molecules-mediated bidirectional interactions between microbes and human cells

Complex molecules-mediated interactions, which are based on the bidirectional information exchange between microbes and human cells, enable the defense against diseases and health maintenance. Recently, diverse single-direction interactions based on active metabolites, immunity factors, and quorum sensing signals have largely been summarized separately. In this review, according to a simplified timeline, we proposed the framework of Molecules-mediated Bidirectional Interactions (MBI) between microbe and humans to decipher and understand their intricate interactions systematically. About the microbe-derived interactions, we summarized various molecules, such as short-chain fatty acids, bile acids, tryptophan catabolites, and quorum sensing molecules, and their corresponding human receptors. Concerning the human-derived interactions, we reviewed the effect of human molecules, including hormones, cytokines, and other circulatory metabolites on microbial characteristics and phenotypes. Finally, we discussed the challenges and trends for developing and deciphering molecule-mediated bidirectional interactions and their potential applications in the guard of human health.

Where Biology Meets Engineering: Scaling Up Microbial Nutraceuticals to Bridge Nutrition, Therapeutics, and Global Impact

The global nutraceutical industry is experiencing a paradigm shift, driven by an increasing demand for functional foods and dietary supplements that address malnutrition and chronic diseases such as obesity, diabetes, cardiovascular conditions, and cancer. Traditional plant- and animal-derived nutraceuticals face limitations in scalability, cost, and environmental impact, paving the way for microbial biotechnology as a sustainable alternative. Microbial cells act as bio-factories, converting nutrients like glucose and amino acids into valuable nutraceutical products such as polyunsaturated fatty acids (PUFAs), peptides, and other bioactive compounds. By harnessing their natural metabolic capabilities, microorganisms efficiently synthesize these bioactive compounds, making microbial production a sustainable and effective approach for nutraceutical development. This review explores the transformative role of microbial platforms in the production of nutraceuticals, emphasizing advanced fermentation techniques, synthetic biology, and metabolic engineering. It addresses the challenges of optimizing microbial strains, ensuring product quality, and scaling production while navigating regulatory frameworks. Furthermore, the review highlights cutting-edge technologies such as CRISPR/Cas9 for genome editing, adaptive evolution for strain enhancement, and bioreactor innovations to enhance yield and efficiency. With a focus on sustainability and precision, microbial production is positioned as a game-changer in the nutraceutical industry, offering eco-friendly and scalable solutions to meet global health needs. The integration of omics technologies and the exploration of novel microbial sources hold the potential to revolutionize this field, aligning with the growing consumer demand for innovative and functional bioactive products.

Electrode functional microorganisms in bioelectrochemical systems and its regulation: A review

Bioelectrochemical systems (BES) as environmental remediation biotechnologies have boomed in the last two decades. Although BESs combined technologies with electro-chemistry, -biology, and -physics, microorganisms and biofilms remain at their core. In this review, various functional microorganisms in BESs for CO2 reduction, dehalogenation, nitrate, phosphate, and sulfate reduction, metal removal, and volatile organic compound oxidation are summarized and compared in detail. Moreover, interrelationship regulation approaches for functional microorganisms and methods for electroactive biofilm development, such as targeted electrode surface modification, chemical treatment, physical revealing, biological optimization, and genetic programming are pointed out. This review provides promising guidance and suggestions for the selection of microbial inoculants and provides an analysis of the role of individual microorganisms in mixed microbial communities and its metabolisms.

The Role of Quorum Sensing in Phage Lifecycle Decision: A Switch Between Lytic and Lysogenic Pathways

Phages, the most abundant and diverse lifeforms on Earth, require strict parasitism for survival. During infection, temperate phages integrate both intracellular and extracellular host information to decide between lysis and lysogeny for replication. While various environmental and physiological factors influence the lysis-lysogeny decision, recent insights into phage-bacterium interactions reveal phages' ability to communicate with and influence bacteria, leveraging the host's quorum sensing system or small molecular signals. This article provides a succinct overview of current research advancements in this field, enhancing our understanding of phage-host dynamics and providing insights into bacteria's multicellular behavior in antiviral defense.

Disrupting the bacterial language: quorum quenching and its applications

Quorum sensing (QS) is a bacterial communication method closely linked with population density and regulates biofilm formation and the secretion of virulence factors through the release, recognition, and prompt response to small molecule signals. At low cell density, each bacterium produces a low concentration of QS signals that diffuse or are actively transported into the external environment. The accumulated QS signals in the external environment reach a threshold concentration when the bacterial population attains a certain density, enabling effective recognition and interaction of bacterial QS signals with their receptors. This leads to coordinated gene expression and various biological activities across the bacterial population. Targeting the QS system presents a promising strategy to hinder biofilm formation and virulence factor secretion, providing a potential approach to control bacterial growth and reproduction. This study aims to analyze the intercellular mechanisms of quorum quenching (QQ), which focuses on disrupting bacterial signal molecules to keep their concentration below the threshold and preventing the expression of specific pathogenic factors. The applications of QQ in different fields are also reviewed, underscoring its potential as a novel treatment for bacterial infections.

Diversity and activity of AHL-lactonases in Bacillus spp. from various environments

Disrupting quorum sensing (QS) pathways in animal and plant pathogenic bacteria is an effective strategy to mitigate infections without promoting antibiotic and pesticide resistance. This approach inhibits the production of virulence factors, biofilm formation, and toxin production, reducing bacterial pathogenicity. In plant health protection, Bacillus spp. are extensively researched and utilized as biocontrol agents; however, the potential of their AHL-lactonase-producing ability, which plays a key role as a QS inhibitor of Gram-negative pathogens, remains largely unexplored. This study examined the activity and diversity of QQ enzymes from Bacillus spp. isolates obtained from various natural sources, confirming their presence in previously unreported environments associated with agricultural fields (straw and manure). Our findings show that AiiA lactonase is the most dominant and highly conserved AHL-lactonase among Bacillus isolates from bulk soil, manure, and straw. Despite its sequence conservation, we observed significant variation in AiiA lactonase activities toward the N-hexanoyl-DL-homoserine lactone (C6-HSL) substrate. Furthermore, in silico analysis suggested that the Bacillus sp. YtnP lactonase may have a lower affinity for C6-HSL compared to AiiA lactonase. Finally, this research presents a selection of Bacillus isolates with high AiiA lactonase activity for potential testing against plant pathogens.

Long-term homeostasis in microbial consortia via auxotrophic cross-feeding

Synthetic microbial consortia are collections of multiple strains or species of engineered organisms living in a shared ecosystem. Because they can separate metabolic tasks among different strains, synthetic microbial consortia have myriad applications in developing biomaterials, biomanufacturing, and biotherapeutics. However, synthetic consortia often require burdensome control mechanisms to ensure that the members of the community remain at the correct proportions. This is especially true in continuous culture systems in which slight differences in growth rates can lead to extinctions. Here, we present a simple method for controlling consortia proportions using cross-feeding in continuous auxotrophic co-culture. We use mutually auxotrophic E. coli with different essential gene deletions and regulate the growth rates of members of the consortium via cross-feeding of the missing nutrients in each strain. We demonstrate precise regulation of the co-culture steady-state ratio by exogenous addition of the missing nutrients. We also model the co-culture's behavior using a system of ordinary differential equations that enable us to predict its response to changes in nutrient concentrations. Our work provides a powerful tool for consortia proportion control with minimal metabolic costs to the constituent strains.

Harnessing Microbial Signal Transduction Systems in Natural and Synthetic Consortia for Biotechnological Applications

Signal transduction is crucial for communication and cellular response in microbial communities. Consortia rely on it for effective communication, responding to changing environmental conditions, establishing community structures, and performing collective behaviors. Microbial signal transduction can be through quorum sensing (QS), two-component signal transduction systems, biofilm formation, nutrient sensing, chemotaxis, horizontal gene transfer stress response, and so forth. The consortium uses small signaling molecules in QS to regulate gene expression and coordinate intercellular communication and behaviors. Biofilm formation allows cells to adhere and aggregate, promoting species interactions and environmental stress resistance. Chemotaxis enables directional movement toward or away from chemical gradients, promoting efficient resource utilization and community organization within the consortium. In recent years, synthetic microbial consortia have gained attention for their potential applications in biotechnology and bioremediation. Understanding signal transduction in natural and synthetic microbial consortia is important for gaining insights into community dynamics, evolution, and ecological function. It can provide strategies for biotechnological innovation for enhancing biosensors, biodegradation, bioenergy efficiency, and waste reduction. This review provides compelling insight that will advance our understanding of microbial signal transduction dynamics and its role in orchestrating microbial interactions, which facilitate coordination, cooperation, gene expression, resource allocation, and trigger specific responses that determine community success.

Strategies and tools to construct stable and efficient artificial coculture systems as biosynthetic platforms for biomass conversion

Inspired by the natural symbiotic relationships between diverse microbial members, researchers recently focused on modifying microbial chassis to create artificial coculture systems using synthetic biology tools. An increasing number of scientists are now exploring these systems as innovative biosynthetic platforms for biomass conversion. While significant advancements have been achieved, challenges remain in maintaining the stability and productivity of these systems. Sustaining an optimal population ratio over a long time period and balancing anabolism and catabolism during cultivation have proven difficult. Key issues, such as competitive or antagonistic relationships between microbial members, as well as metabolic imbalances and maladaptation, are critical factors affecting the stability and productivity of artificial coculture systems. In this article, we critically review current strategies and methods for improving the stability and productivity of these systems, with a focus on recent progress in biomass conversion. We also provide insights into future research directions, laying the groundwork for further development of artificial coculture biosynthetic platforms.

Palmitoleic acid inhibits Pseudomonas aeruginosa quorum sensing activation and protects lungs from infectious injury

BACKGROUND

Unsaturated fatty acids targeting quorum sensing (QS) system have shown potential application in reducing bacterial virulence. We aim to investigate the effect of palmitoleic acid (PMA) on P. aeruginosa QS activation, and its impact on infection-induced lung injury.

METHODS

The influence of PMA on QS signaling molecule (3OC12-HSL and C4-HSL) concentrations, pyocyanin production, and QS gene transcription levels were examined in wildtype PAO1 culture. The roles of PMA in reducing infection-induced injury were assessed in human bronchial epithelial BEAS-2B cells and mouse lung infection models, respectively. PMA levels and QS signaling molecule concentrations were tested in the bronchoalveolar lavage fluid (BALF) of bronchiectasis patients with first-time detection of P. aeruginosa infection.

RESULTS

PMA administration dose-dependently suppressed the expression of QS signaling molecules, pyocyanin, and QS genes during the logarithmic stage of bacterial growth. In BEAS-2B cells, PMA-treated PAO1 filtrates significantly reduced cell apoptosis and expression of IL-8 and IL-6. In mouse lung infection models, prophylactically oral administration of PMA significantly downregulated the expression of P. aeruginosa QS signals and QS genes (lasR, rhlR, rhlI, lasB, rhlA, phzA1, phnA) in lungs, and relieved neutrophilic airway inflammation. Finally, PMA levels were negatively correlated with the concentrations of both 3OC12-HSL and C4-HSL in BALF of bronchiectasis patients, and positively correlated with their forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1.0).

CONCLUSION

Our findings show that PMA inhibits P. aeruginosa QS activation and protects lungs from injury caused by bacterial virulence. Hence, PMA may serve as a potential anti-QS agent against P. aeruginosa infection and would help to alleviate lung injury in bronchiectasis patients.

Assembly of functional microbial ecosystems: from molecular circuits to communities

Microbes compete and cooperate with each other via a variety of chemicals and circuits. Recently, to decipher, simulate, or reconstruct microbial communities, many researches have been engaged in engineering microbiomes with bottom-up synthetic biology approaches for diverse applications. However, they have been separately focused on individual perspectives including genetic circuits, communications tools, microbiome engineering, or promising applications. The strategies for coordinating microbial ecosystems based on different regulation circuits have not been systematically summarized, which calls for a more comprehensive framework for the assembly of microbial communities. In this review, we summarize diverse cross-talk and orthogonal regulation modules for de novo bottom-up assembling functional microbial ecosystems, thus promoting further consortia-based applications. First, we review the cross-talk communication-based regulations among various microbial communities from intra-species and inter-species aspects. Then, orthogonal regulations are summarized at metabolites, transcription, translation, and post-translation levels, respectively. Furthermore, to give more details for better design and optimize various microbial ecosystems, we propose a more comprehensive design-build-test-learn procedure including function specification, chassis selection, interaction design, system build, performance test, modeling analysis, and global optimization. Finally, current challenges and opportunities are discussed for the further development and application of microbial ecosystems.

Molecular Communication of Microbial Plant Biostimulants in the Rhizosphere Under Abiotic Stress Conditions

Microbial plant biostimulants offer a promising, sustainable solution for enhancing plant growth and resilience, particularly under abiotic stress conditions such as drought, salinity, extreme temperatures, and heavy metal toxicity. These biostimulants, including plant growth-promoting rhizobacteria, mycorrhizal fungi, and nitrogen-fixing bacteria, enhance plant tolerance through mechanisms such as phytohormone production, nutrient solubilization, osmotic adjustment, and antioxidant enzyme activation. Advances in genomics, metagenomics, transcriptomics, and proteomics have significantly expanded our understanding of plant-microbe molecular communication in the rhizosphere, revealing mechanisms underlying these interactions that promote stress resilience. However, challenges such as inconsistent field performance, knowledge gaps in stress-related molecular signaling, and regulatory hurdles continue to limit broader biostimulant adoption. Despite these challenges, microbial biostimulants hold significant potential for advancing agricultural sustainability, particularly amid climate change-induced stresses. Future studies and innovation, including Clustered Regularly Interspaced Short Palindromic Repeats and other molecular editing tools, should optimize biostimulant formulations and their application for diverse agro-ecological systems. This review aims to underscore current advances, challenges, and future directions in the field, advocating for a multidisciplinary approach to fully harness the potential of biostimulants in modern agriculture.

Challenges and opportunities of phage therapy for Klebsiella pneumoniae infections

Traditional antibiotics have been effective in many cases. However, the rise in multidrug-resistant bacteria has diminished their therapeutic efficacy, signaling the dawn of an era beyond antibiotics. The challenge of multidrug resistance in Klebsiella pneumoniae is particularly critical, with increasing global mortality and resistance rates. Therefore, the development of alternative therapies to antibiotics is urgently needed. Phages, which are natural predators of bacteria, have inherent advantages. However, comprehensive information on K. pneumoniae phages is lacking in current literature. This review aims to analyze and summarize relevant studies, focusing on the present state of phage therapy for K. pneumoniae infections. This includes an examination of treatment methodologies, associated challenges, strategies, new phage technologies, clinical trial safety and efficacy, regulatory issues, and future directions for phage therapy development. Enhancing phage technology is crucial for addressing the evolving threat of multidrug-resistant K. pneumoniae.

Nisin-relevant antimicrobial peptides: synthesis strategies and applications

Small pentacyclic peptides, represented by nisin, have been successfully utilized as preservatives in the food industry and have evolved into a paradigm for understanding the genetic structure, expression, and control of genes created by lantibiotics. Due to the ever-increasing antibiotic resistance, nisin-relevant antimicrobial peptides have received much attention, which calls for a summarization of their synthesis, modification and applications. In this review, we first provided a timeline of select highlights in nisin biosynthesis and engineering. Then, we outlined the current developments in nisin synthesis. We also provided an overview of the engineering, screening, and production of nisin-relevant antimicrobial peptides based on enzyme alteration, substrate modification, and sequence mining. Furthermore, an updated summary of applications of nisin-relevant antimicrobial peptides has been developed for food applications. Finally, this study offers insights into emerging technologies, limitations and the future development of nisin-relevant antimicrobial peptides for pathogen inhibition, food preservatives, and improved health.

Engineering a biomimicking strategy for discovering nonivamide-based quorum-sensing inhibitors for controlling bacterial infection

The overuse of antibiotics over an extended period has led to increasing antibiotic resistance in pathogenic bacteria, culminating in what is now considered a global health crisis. To tackle the escalating disaster caused by multidrug-resistant pathogens, the development of new bactericides with new action mechanism is highly necessary. In this study, using a biomimicking strategy, a series of new nonivamide derivatives that feature an isopropanolamine moiety [the structurally similar to the diffusible signal factor (DSF) of Xanthomonas spp.] were prepared for serving as potential quorum-sensing inhibitors (QSIs). After screening and investigation of their rationalizing structure-activity relationships (SARs), compound A26 was discovered as the most optimal active molecule, with EC50 values of 9.91 and 7.04 μg mL-1 against Xanthomonas oryzae pv oryzae (Xoo) and Xanthomonas axonopodis pv. citri (Xac). A docking study showed that compound A26 exhibited robust interactions with Glu A: 161 of RpfF, which was strongly evidenced by fluorescence titration assay (KA value for Xoo RpfF-A26 = 104.8709 M-1). Furthermore, various bioassays showed that compound A26 could inhibit various bacterial virulence factors, including biofilm formation, extracellular polysaccharides (EPS), extracellular enzyme activity, DSF production, and swimming motility. In addition, in vivo anti-Xoo results showed that compound A26 had excellent control efficiency (curative activity: 43.55 %; protective activity: 42.56 %), surpassing that of bismerthiazol and thiodiazole copper by approximately 8.0%-37.3 %. Overall, our findings highlight a new paradigm wherein nonivamide derivatives exhibit potential in combating pathogen resistance issues by inhibiting bacterial quorum sensing systems though attributing to their new molecular skeleton, novel mechanisms of action, and non-toxic features.

Current strategies for monitoring and controlling bacterial biofilm formation on medical surfaces

Biofilms, intricate microbial communities that attach to surfaces, especially medical devices, form an exopolysaccharide matrix, which enables bacteria to resist environmental pressures and conventional antimicrobial agents, leading to the emergence of multi-drug resistance. Biofilm-related infections associated with medical devices are a significant public health threat, compromising device performance. Therefore, developing effective methods for supervising and managing biofilm growth is imperative. This in-depth review presents a systematic overview of strategies for monitoring and controlling bacterial biofilms. We first outline the biofilm creation process and its regulatory mechanisms. The discussion then progresses to advancements in biosensors for biofilm detection and diverse treatment strategies. Lastly, this review examines the obstacles and new perspectives associated with this domain to facilitate the advancement of innovative monitoring and control solutions. These advancements are vital in combating the spread of multi drug-resistant bacteria and mitigating public health risks associated with infections from biofilm formation on medical instruments.

Rapid Revealing of Quorum Sensing (QS)-Regulated PLA, Biofilm and Lysine Targets of Lactiplantibacillus plantarum L3

Quorum sensing (QS) can regulate the production of multiple functional factors in bacteria, but the process of identifying its regulatory targets is very complex and labor-intensive. In this study, an efficient and rapid method to find QS targets through prediction was used. The genome of Lactiplantibacillus plantarum (L. plantarum) L3 was sequenced and characterized, and then linked the L. plantarum L3 genome to the STRING database for QS system regulatory target prediction. A total of 3,167,484 base pairs (bps) were examined from the genome of L. plantarum L3, and 30 QS-related genes were discovered (including luxS). The STRING database prediction indicated that the 30 QS-related genes are mainly involved in the regulation of nine metabolic pathways. Furthermore, metE, metK, aroB, cysE, and birA1 were predicted to be regulatory targets of the LuxS/AI-2 QS system, and these five targets were validated based on quantitative real-time PCR and content determination. Successful elucidation of the LuxS/AI-2 QS system's key targets and regulation mechanism in L. plantarum L3 demonstrated the effectiveness of the new approach for predicting QS targets and provides a scientific basis for future work on improving regulation of functional factor production.

Multi-omics signatures reveal genomic and functional heterogeneity of Cutibacterium acnes in normal and diseased skin

Cutibacterium acnes is the most abundant bacterium of the human skin microbiome since adolescence, participating in both skin homeostasis and diseases. Here, we demonstrate individual and niche heterogeneity of C. acnes from 1,234 isolate genomes. Skin disease (atopic dermatitis and acne) and body site shape genomic differences of C. acnes, stemming from horizontal gene transfer and selection pressure. C. acnes harbors characteristic metabolic functions, fewer antibiotic resistance genes and virulence factors, and a more stable genome compared with Staphylococcus epidermidis. Integrated genome, transcriptome, and metabolome analysis at the strain level unveils the functional characteristics of C. acnes. Consistent with the transcriptome signature, C. acnes in a sebum-rich environment induces toxic and pro-inflammatory effects on keratinocytes. L-carnosine, an anti-oxidative stress metabolite, is up-regulated in the C. acnes metabolome from atopic dermatitis and attenuates skin inflammation. Collectively, our study reveals the joint impact of genes and the microenvironment on C. acnes function.

Multi-omic analysis tools for microbial metabolites prediction

How to resolve the metabolic dark matter of microorganisms has long been a challenging problem in discovering active molecules. Diverse omics tools have been developed to guide the discovery and characterization of various microbial metabolites, which make it gradually possible to predict the overall metabolites for individual strains. The combinations of multi-omic analysis tools effectively compensates for the shortcomings of current studies that focus only on single omics or a broad class of metabolites. In this review, we systematically update, categorize and sort out different analysis tools for microbial metabolites prediction in the last five years to appeal for the multi-omic combination on the understanding of the metabolic nature of microbes. First, we provide the general survey on different updated prediction databases, webservers, or software that based on genomics, transcriptomics, proteomics, and metabolomics, respectively. Then, we discuss the essentiality on the integration of multi-omics data to predict metabolites of different microbial strains and communities, as well as stressing the combination of other techniques, such as systems biology methods and data-driven algorithms. Finally, we identify key challenges and trends in developing multi-omic analysis tools for more comprehensive prediction on diverse microbial metabolites that contribute to human health and disease treatment.

Veratryl Alcohol Attenuates the Virulence and Pathogenicity of Pseudomonas aeruginosa Mainly via Targeting las Quorum-Sensing System

Pseudomonas aeruginosa is an opportunistic pathogen that usually causes chronic infections and even death in patients. The treatment of P. aeruginosa infection has become more challenging due to the prevalence of antibiotic resistance and the slow pace of new antibiotic development. Therefore, it is essential to explore non-antibiotic methods. A new strategy involves screening for drugs that target the quorum-sensing (QS) system. The QS system regulates the infection and drug resistance in P. aeruginosa. In this study, veratryl alcohol (VA) was found as an effective QS inhibitor (QSI). It effectively suppressed the expression of QS-related genes and the subsequent production of virulence factors under the control of QS including elastase, protease, pyocyanin and rhamnolipid at sub-inhibitory concentrations. In addition, motility activity and biofilm formation, which were correlated with the infection of P. aeruginosa, were also suppressed by VA. In vivo experiments demonstrated that VA could weaken the pathogenicity of P. aeruginosa in Chinese cabbage, Drosophila melanogaster, and Caenorhabditis elegans infection models. Molecular docking, combined with QS quintuple mutant infection analysis, identified that the mechanism of VA could target the LasR protein of the las system mainly. Moreover, VA increased the susceptibility of P. aeruginosa to conventional antibiotics of tobramycin, kanamycin and gentamicin. The results firstly demonstrate that VA is a promising QSI to treat infections caused by P. aeruginosa.

Investigating luxS gene expression in lactobacilli along lab-scale cocoa fermentations

Previous metagenomic analyses have suggested that lactobacilli present potential for Quorum Sensing (QS) in cocoa fermentation, and in the present research, laboratory scale fermentations were carried out to monitor the expression of luxS, a universal marker of QS. For that, 96 h-fermentations were studied, as follows: F0 (non inoculated control), F1 (inoculated with yeasts, lactic acid bacteria, and acetic acid bacteria), F2 (inoculated with yeasts and acetic acid bacteria), F3 (inoculated with yeasts only). The parameters evaluated were: plate counting, quantification of key enzymes and analysis of volatile organic compounds associated with key sensory descriptors, using headspace gas chromatography-mass spectrometry (GC-MS). Furthermore, QS was estimated by the quantification of the expression of luxS genes by Reverse Transcriptase Real-Time PCR. The results demonstrated that microbial succession occurred in pilot scale fermentations, but no statistical differences for microbial enumeration and α-diversity index were observed among experiments and control. Moreover, it was not possible to make conclusive correlations of enzymatic profile and fermenting microbiota, likely due to the intrinsic activity of plant hydrolases. Regarding to the expression of luxS genes, in Lactiplantibacillus plantarum they were active along the fermentation, but for Limosilactobacillus fermentum, luxS was expressed only at early and middle phases. Correlation analysis of luxS expression and production of volatile metabolites evidenced a possible negative association of Lp. Plantarum with fermentation quality. In conclusion, these data corroborate former shotgun metagenomic analysis by demonstrating the expression of luxS by lactobacilli in pilot scale cocoa fermentation and evidence Lp. Plantarum is the main lactic acid bacteria related to its expression.

Anti-Biofilm and Anti-Quorum-Sensing Activity of Inula Extracts: A Strategy for Modulating Chromobacterium violaceum Virulence Factors

The formation of microbial biofilm is a self-organizing process among bacterial cells, regulated by quorum-sensing (QS) mechanisms, contributing to development of infections. These processes, either separately or in combination, significantly contribute to bacterial resistance to antibiotics and disinfectants. A novel approach to addressing the challenge of treating infections due to antibacterial resistance involves the use of plant metabolites. In recent years, there has been increasing recognition of different phytochemicals as potential modulators. In our study, we evaluated the synergistic effect of chloroform and methanol extracts from Inula species against key virulence factors, including biofilm formation, violacein production, and swarming motility. Each of the 11 examined plant extracts demonstrated the ability to reduce biofilms and pigment synthesis in C. violaceum. Two of the extracts from I. britannica exhibited significant anti-biofilm and anti-quorum-sensing effects with over 80% inhibition. Their inhibitory effect on violacein synthesis indicates their potential as anti-QS agents, likely attributed to their high concentration of terpenoids (triterpenoids, sesquiterpene lactones, and diterpenoids). Scanning electron microscopy revealed a notable reduction in biofilm biomass, along with changes in biofilm architecture and cell morphology. Additionally, fluorescence microscopy revealed the presence of metabolically inactive cells, indicating the potent activity of the extracts during treatment. These new findings underscore the effectiveness of the plant extracts from the genus Inula as potential anti-virulent agents against C. violaceum. They also propose a promising strategy for preventing or treating its biofilm formation.

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.

Nanoparticle/Engineered Bacteria Based Triple-Strategy Delivery System for Enhanced Hepatocellular Carcinoma Cancer Therapy

Background

New treatment modalities for hepatocellular carcinoma (HCC) are desperately critically needed, given the lack of specificity, severe side effects, and drug resistance with single chemotherapy. Engineered bacteria can target and accumulate in tumor tissues, induce an immune response, and act as drug delivery vehicles. However, conventional bacterial therapy has limitations, such as drug loading capacity and difficult cargo release, resulting in inadequate therapeutic outcomes. Synthetic biotechnology can enhance the precision and efficacy of bacteria-based delivery systems. This enables the selective release of therapeutic payloads in vivo.

Methods

In this study, we constructed a non-pathogenic Escherichia coli (E. coli) with a synchronized lysis circuit as both a drug/gene delivery vehicle and an in-situ (hepatitis B surface antigen) Ag (ASEc) producer. Polyethylene glycol (CHO-PEG2000-CHO)-poly(ethyleneimine) (PEI25k)-citraconic anhydride (CA)-doxorubicin (DOX) nanoparticles loaded with plasmid encoded human sulfatase 1 (hsulf-1) enzyme (PNPs) were anchored on the surface of ASEc (ASEc@PNPs). The composites were synthesized and characterized. The in vitro and in vivo anti-tumor effect of ASEc@PNPs was tested in HepG2 cell lines and a mouse subcutaneous tumor model.

Results

The results demonstrated that upon intravenous injection into tumor-bearing mice, ASEc can actively target and colonise tumor sites. The lytic genes to achieve blast and concentrated release of Ag significantly increased cytokine secretion and the intratumoral infiltration of CD4/CD8+T cells, initiated a specific immune response. Simultaneously, the PNPs system releases hsulf-1 and DOX into the tumor cell resulting in rapid tumor regression and metastasis prevention.

Conclusion

The novel drug delivery system significantly suppressed HCC in vivo with reduced side effects, indicating a potential strategy for clinical HCC therapy.

A quorum-sensing regulatory cascade for siderophore-mediated iron homeostasis in Chromobacterium violaceum

Iron is a transition metal used as a cofactor in many biochemical reactions. In bacteria, iron homeostasis involves Fur-mediated de-repression of iron uptake systems, such as the iron-chelating compounds siderophores. In this work, we identified and characterized novel regulatory systems that control siderophores in the environmental opportunistic pathogen Chromobacterium violaceum. Screening of a 10,000-transposon mutant library for siderophore halos identified seven possible regulatory systems involved in siderophore-mediated iron homeostasis in C. violaceum. Further characterization revealed a regulatory cascade that controls siderophores involving the transcription factor VitR acting upstream of the quorum-sensing (QS) system CviIR. Mutation of the regulator VitR led to an increase in siderophore halos, and a decrease in biofilm, violacein, and protease production. We determined that these effects occurred due to VitR-dependent de-repression of vioS. Increased VioS leads to direct inhibition of the CviR regulator by protein-protein interaction. Indeed, insertion mutations in cviR and null mutations of cviI and cviR led to an increase of siderophore halos. RNA-seq of the cviI and cviR mutants revealed that CviR regulates CviI-dependent and CviI-independent regulons. Classical QS-dependent processes (violacein, proteases, and antibiotics) were activated at high cell density by both CviI and CviR. However, genes related to iron homeostasis and many other processes were regulated by CviR but not CviI, suggesting that CviR acts without its canonical CviI autoinducer. Our data revealed a complex regulatory cascade involving QS that controls siderophore-mediated iron homeostasis in C. violaceum.IMPORTANCEThe iron-chelating compounds siderophores play a major role in bacterial iron acquisition. Here, we employed a genetic screen to identify novel siderophore regulatory systems in Chromobacterium violaceum, an opportunistic human pathogen. Many mutants with increased siderophore halos had transposon insertions in genes encoding transcription factors, including a novel regulator called VitR, and CviR, the regulator of the quorum-sensing (QS) system CviIR. We found that VitR is upstream in the pathway and acts as a dedicated repressor of vioS, which encodes a direct CviR-inhibitory protein. Indeed, all QS-related phenotypes of a vitR mutant were rescued in a vitRvioS mutant. At high cell density, CviIR activated classical QS-dependent processes (violacein, proteases, and antibiotics production). However, genes related to iron homeostasis and type-III and type-VI secretion systems were regulated by CviR in a CviI- or cell density-independent manner. Our data unveil a complex regulatory cascade integrating QS and siderophores in C. violaceum.

Abiotic Small Molecule Inhibitors and Activators of the LasR Quorum Sensing Receptor in Pseudomonas aeruginosa with Potencies Comparable or Surpassing N-Acyl Homoserine Lactones

The opportunistic pathogen Pseudomonas aeruginosa controls almost 10% of its genome, including myriad virulence genes, via a cell-to-cell chemical communication system called quorum sensing (QS). Small molecules that either inhibit or activate QS in P. aeruginosa represent useful research tools to study the role of this signaling pathway in infection and interrogate its viability as an antivirulence target. However, despite active research in this area over the past 20+ years, there are relatively few synthetic compounds known to strongly inhibit or activate QS in P. aeruginosa. Most reported QS modulators in this pathogen are of low potency or have structural liabilities that limit their application in biologically relevant environments such as mimics of the native N-acyl l-homoserine lactone (AHL) signals. Here, we report the results of a high-throughput screen for abiotic small molecules that target LasR, a key QS regulator in P. aeruginosa. We screened a 25,000-compound library and discovered four new structural classes of abiotic LasR modulators. These compounds include antagonists that surpass the potency of all known AHL-type compounds and mimetics thereof, along with an agonist with potency approaching that of LasR's native ligand. The novel structures of this compound set, along with their anticipated robust physicochemical profiles, underscore their potential value as probe molecules to interrogate the roles of QS in this formidable pathogen.

Baicalin Weakens the Virulence of Porcine Extraintestinal Pathogenic Escherichia coli by Inhibiting the LuxS/AI-2 Quorum-Sensing System

Porcine extraintestinal pathogenic Escherichia coli (ExPEC) is a pathogenic bacterium that causes huge economic losses to the pig farming industry and considerably threatens human health. The quorum sensing (QS) system plays a crucial role in the survival and pathogenesis of pathogenic bacteria. Hence, it is a viable approach to prevent ExPEC infection by compromising the QS system, particularly the LuxS/AI-2 system. In this study, we investigated the effects of baicalin on the LuxS/AI-2 system of ExPEC. Baicalin at concentrations of 25, 50, and 100 μg/mL significantly diminished the survival ability of ExPEC in hostile environments and could inhibit the biofilm formation and autoagglutination ability in ExPEC. Moreover, baicalin dose-dependently decreased the production of AI-2 and down-regulated the expression level of luxS in PCN033. These results suggest that baicalin can weaken the virulence of PCN033 by inhibiting the LuxS/AI-2 system. After the gene luxS was deleted, AI-2 production in PCN033 was almost completely eliminated, similar to the effect of baicalin on the production of AI-2 in PCN033. This indicates that baicalin reduced the production of AI-2 by inhibiting the expression level of luxS in ExPEC. In addition, the animal experiment further showed the potential of baicalin as a LuxS/AI-2 system inhibitor to prevent ExPEC infection. This study highlights the potential of baicalin as a natural quorum-sensing inhibitor for therapeutic applications in preventing ExPEC infection by targeting the LuxS/AI-2 system.

Total transcriptome response for tyrosol exposure in Aspergillus nidulans

Although tyrosol is a quorum-sensing molecule of Candida species, it has antifungal activity at supraphysiological concentrations. Here, we studied the effect of tyrosol on the physiology and genome-wide transcription of Aspergillus nidulans to gain insight into the background of the antifungal activity of this compound. Tyrosol efficiently reduced germination of conidia and the growth on various carbon sources at a concentration of 35 mM. The growth inhibition was fungistatic rather than fungicide on glucose and was accompanied with downregulation of 2199 genes related to e.g. mitotic cell cycle, glycolysis, nitrate and sulphate assimilation, chitin biosynthesis, and upregulation of 2250 genes involved in e.g. lipid catabolism, amino acid degradation and lactose utilization. Tyrosol treatment also upregulated genes encoding glutathione-S-transferases (GSTs), increased specific GST activities and the glutathione (GSH) content of the cells, suggesting that A. nidulans can detoxify tyrosol in a GSH-dependent manner even though this process was weak. Tyrosol did not induce oxidative stress in this species, but upregulated "response to nutrient levels", "regulation of nitrogen utilization", "carbon catabolite activation of transcription" and "autophagy" genes. Tyrosol may have disturbed the regulation and orchestration of cellular metabolism, leading to impaired use of nutrients, which resulted in growth reduction.

Microbiota substances modulate dendritic cells activity: A critical view

Contemporary research in the field of microbiota shows that commensal bacteria influence physiological activity of different organs and systems of a human organism, such as brain, lungs, immune and metabolic systems. This influence is realized by various processes. One of them is trough modulation of immune mechanisms. Interactions between microbiota and the human immune system are known to be complex and ambiguous. Dendritic cells (DCs) are unique cells, which initiate the development and polarization of adaptive immune response. These cells also interconnect native and specific immune reactivity. A large set of biochemical signals from microbiota in the form of different microbiota associated molecular patterns (MAMPs) and bacterial metabolites that act locally and distantly in the human organism. As a result, commensal bacteria influence the maturity and activity of dendritic cells and affect the overall immune reactivity of the human organism. It then determines the response to pathogenic microorganisms, inflammation, associated with different pathological conditions and even affects the effectiveness of vaccination.

Life at the borderlands: microbiomes of interfaces critical to One Health

Microbiomes are foundational components of the environment that provide essential services relating to food security, carbon sequestration, human health, and the overall well-being of ecosystems. Microbiota exert their effects primarily through complex interactions at interfaces with their plant, animal, and human hosts, as well as within the soil environment. This review aims to explore the ecological, evolutionary, and molecular processes governing the establishment and function of microbiome-host relationships, specifically at interfaces critical to One Health-a transdisciplinary framework that recognizes that the health outcomes of people, animals, plants, and the environment are tightly interconnected. Within the context of One Health, the core principles underpinning microbiome assembly will be discussed in detail, including biofilm formation, microbial recruitment strategies, mechanisms of microbial attachment, community succession, and the effect these processes have on host function and health. Finally, this review will catalogue recent advances in microbiology and microbial ecology methods that can be used to profile microbial interfaces, with particular attention to multi-omic, advanced imaging, and modelling approaches. These technologies are essential for delineating the general and specific principles governing microbiome assembly and functions, mapping microbial interconnectivity across varying spatial and temporal scales, and for the establishment of predictive frameworks that will guide the development of targeted microbiome-interventions to deliver One Health outcomes.

Metagenomic analysis reveals impact of acyl homoserine endolipid-like signaling molecules on the aqueous sediment resistome under florfenicol stress

Quorum sensing potentially helps microorganisms adapt to antibiotic stress encountered in the environment. This experiment investigated the effect of acyl homoserine endolipid-like signaling molecules on microbial antibiotic resistance gene structures in aqueous sediments under florfenicol stress. Additional acyl homoserine endolipid-like signaling molecules (AHLs) alter the structure of multidrug resistance genes in florfenicol-stressed sediments, particularly the multidrug resistance efflux pump gene family. Prophages and integrative and conjugative elements (ICEs) determined the resistance genes structure, and pathways related to mobile genetic elements (MGEs) transfer may play an essential role in this process. The practical application of AHLs to regulate quorum sensing systems may alter bacterial stress responses to environmental florfenicol residues, thereby reducing the development of antibiotic resistance in the environment.

Communication mediated interaction between bacteria and microalgae advances photogranulation

Recently, photogranules composed of bacteria and microalgae for carbon-negative nitrogen removal receive extensive attention worldwide, yet which type of bacteria is helpful for rapid formation of photogranules and whether they depend on signaling communication remain elusive. Varied signaling communication was analyzed using metagenomic method among bacteria and microalgae in via of two types of experimentally verified signaling molecule from bacteria to microalgae, which include indole-3-acetic acid (IAA) and N-acyl homoserine lactones (AHLs) during the operation of photo-bioreactors. Signaling communication is helpful for the adaptability of bacteria to survive with algae. Compared with non-signaling bacteria, signaling bacteria more easily adapt to the varied conditions, evidenced by the increased abundance in the operated reactors. Signaling bacteria are easier to enter the phycosphere, and they dominate the interactions between bacteria and algae rather than non-signaling bacteria. The co-abundance groups (CAGs) with signaling bacteria possess higher abundance than that without signaling bacteria (22.27 % and 6.67 %). Importantly, signaling bacteria accessibly interact with microalgae, which possess higher degree centralities and 32.50 % of them are keystone nodes in the network, in contrast to only 18.66 % of non-signaling bacteria. Thauera carrying both IAA and AHLs synthase genes are highly enriched and positively correlated with nitrogen removal rate. Our work not only highlights the essential roles of signaling communication between microalgae and bacteria in the development of photogranules, but also enriches our understanding of microbial sociobiology.

Unveiling the hidden language of bacteria: anti-quorum sensing strategies for gram-negative bacteria infection control

Quorum sensing (QS) is a communication mechanism employed by many bacteria to regulate gene expression in a population density-dependent manner. It plays a crucial role in coordinating various bacterial behaviors, including biofilm formation, virulence factor production, and antibiotic resistance. However, the dysregulation of QS can lead to detrimental effects, making it an attractive target for developing novel therapeutic strategies. Anti-QS approaches aim to interfere with QS signaling pathways, inhibiting the communication between bacteria, and disrupting their coordinated activities. Various strategies have been explored to achieve this goal. Advances in understanding QS mechanisms and the discovery of new targets have paved the way for the development of innovative anti-QS approaches. Combining multiple anti-QS strategies or utilizing them in combination with traditional antibiotics holds great promise for combating bacterial infections and addressing the challenges posed by antibiotic resistance. Anti-QS approaches offer a diverse range of strategies including natural compounds, antibody-mediated quorum quenching (QQ), computer-aided drug design for QQ, repurposing of Drugs approved by FDA as anti-QS agents and modulating quorum-sensing molecules which were discussed in detail in this review. This review, comprehensively and for the first time, sheds light on the significance of diverse anti-QS strategies in solving antimicrobial resistance problem in Gram-negative microbial infection.

Seed-Borne Bacterial Diversity of Fescue (Festuca ovina L.) and Properties Study

Rich endophytic bacterial communities exist in fescue (Festuca ovina L.) and play an important role in fescue growth, cold tolerance, drought tolerance and antibiotic tolerance. To screen for probiotics carried by fescue seeds, seven varieties were collected from three different regions of China for isolation by the milled seed method and analyzed for diversity and motility, biofilm and antibiotic resistance. A total of 91 bacterial isolates were obtained, and based on morphological characteristics, 36 representative dominant strains were selected for 16S rDNA sequencing analysis. The results showed that the 36 bacterial strains belonged to four phyla and nine genera. The Firmicutes was the dominant phylum, and Bacillus, Paenibacillus and Pseudomonas were the dominant genera. Most of the strains had motility (80%) and were biofilm-forming (91.7%). In this study, 15 strains were capable of Indole-3-acetic acid (IAA) production, 24 strains were capable of nitrogen fixation, and some strains possessed amylase and protease activities, suggesting their potential for growth promotion. Determination of the minimum inhibitory concentration (MIC) against the bacteria showed that the strains were not resistant to tetracycline and oxytetracycline. Pantoea (QY6, LH4, MS2) and Curtobacterium (YY4) showed resistance to five antibiotics (ampicillin, kanamycin, erythromycin, sulfadiazine and rifampicin). Using Pearson correlation analysis, a significant correlation was found between motility and biofilm, and between biofilm and sulfadiazine. In this study, we screened two strains of Pantoea (QY6, LH4) with excellent growth-promoting ability as well as broad-spectrum antibiotic resistance. which provided new perspectives for subsequent studies on the strong ecological adaptations of fescue, and mycorrhizal resources for endophytic bacteria and plant interactions.

Diesel degradation capability and environmental robustness of strain Pseudomonas aeruginosa WS02

Petroleum hydrocarbon (PHC) degrading bacteria have been frequently discovered. However, in practical application, a single species of PHC degrading bacterium with weak competitiveness may face environmental pressure and competitive exclusion due to the interspecific competition between petroleum-degrading bacteria as well as indigenous microbiota in soil, leading to a reduced efficacy or even malfunction. In this study, the diesel degradation ability and environmental robustness of an endophytic strain Pseudomonas aeruginosa WS02, were investigated. The results show that the cell membrane surface of WS02 was highly hydrophobic, and the strain secreted glycolipid surfactants. Genetic analysis results revealed that WS02 contained multiple metabolic systems and PHC degradation-related genes, indicating that this strain theoretically possesses the capability of oxidizing both alkanes and aromatic hydrocarbons. Gene annotation also showed many targets which coded for heavy metal resistant and metal transporter proteins. The gene annotation-based inference was confirmed by the experimental results: GC-MS analysis revealed that short chain PHCs (C10-C14) were completely degraded, and the degradation of PHCs ranging from C15-C22 were above 90% after 14 d in diesel-exposed culture; Heavy metal (Mn2+, Pb2+ and Zn2+) exposure was found to affect the growth of WS02 to some extent, but not its ability to degrade diesel, and the degradation efficiency was still maintained at 39-59%. WS02 also showed a environmental robustness along with PHC-degradation performance in the co-culture system with other bacterial strains as well as in the co-cultured system with the indigenous microbiota in soil fluid extracted from a PHC-contaminated site. It can be concluded that the broad-spectrum diesel degradation efficacy and great environmental robustness give P. aeruginosa WS02 great potential for application in the remediation of PHC-contaminated soil.

Bacterial quorum sensing controls carbon metabolism to optimize growth in changing environmental conditions

Bacteria sense population density via the cell-cell communication system called quorum sensing (QS). Some QS-regulated phenotypes ( e.g. , secreted enzymes, chelators), are public goods exploitable by cells that stop producing them. We uncovered a phenomenon in which Vibrio cells 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). Methionine/THF synthesis genes are repressed at low cell density when glucose is plentiful and are de-repressed by LuxR at high cell density as glucose becomes limiting. In mixed cultures, QS mutant strains initially co-exist 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 private and public goods within the QS regulon, preventing accumulation of QS-defective mutants.

Biosynthetic potential of the gut microbiome in longevous populations

Gut microbiome plays a pivotal role in combating diseases and facilitating healthy aging, and natural products derived from biosynthetic gene clusters (BGCs) of the human microbiome exhibit significant biological activities. However, the natural products of the gut microbiome in long-lived populations remain poorly understood. Here, we integrated six cohorts of long-lived populations, encompassing a total of 1029 fecal metagenomic samples, and employed the metagenomic single sample assembled BGCs (MSSA-BGCs) analysis pipeline to investigate the natural products and their associated species. Our findings reveal that the BGC composition of the extremely long-lived group differed significantly from that of younger elderly and young individuals across five cohorts. Terpene and Type I PKS BGCs were enriched in the extremely long-lived, whereas cyclic-lactone-autoinducer BGCs were more prevalent in the young. Association analysis indicated that terpene BGCs were strongly associated with the abundance of Akkermansia muciniphila, which was also more abundant in the long-lived elderly across at least three cohorts. We assembled 18 A. muciniphila draft genomes using metagenomic data from the extremely long-lived group across six cohorts and discovered that they all harbor two classes of terpene BGCs, which aligns with the 97 complete genomes of A. muciniphila strains retrieved from the NCBI database. The core domains of these two BGC classes are squalene/phytoene synthases involved in the biosynthesis of tri- and tetraterpenes. Furthermore, the abundance of fecal A. muciniphila was significantly associated with eight types of triterpenoids. Targeted terpenoid metabolomic analysis revealed that two triterpenoids, Holstinone C and colubrinic acid, were enriched in the A. muciniphila culture solution compared to the medium, thereby confirming the production of triterpenoids by A. muciniphila. The natural products derived from the gut of long-lived populations provide intriguing indications of their potential beneficial roles in regulating health.

A novel quorum sensing regulator LuxT contributes to the virulence of Vibrio cholerae

Vibrio cholerae is a waterborne bacterium that primarily infects the human intestine and causes cholera fatality. Quorum sensing (QS) negatively regulates the expression of V. cholerae virulence gene. However, the primary associated mechanisms remain undetermined. This investigation identified a new QS regulator from the TetR family, LuxT, which increases V. cholerae virulence by directly inhibiting hapR expression. HapR is a master QS regulator that suppresses virulence cascade expression. The expression of luxT increased 4.8-fold in the small intestine of infant mice than in Luria-Bertani broth. ΔluxT mutant strain revealed a substantial defect in the colonizing ability of the small intestines. At low cell densities, the expression level of hapR was upregulated by luxT deletion, suggesting that LuxT can suppress hapR transcription. The electrophoretic mobility shift analysis revealed that LuxT directly binds to the hapR promoter region. Furthermore, luxT expression was upregulated by the two-component system ArcB/ArcA, which responses to changes in oxygen levels in response to the host's small intestine's anaerobic signals. In conclusion, this research reveals a novel cell density-mediated virulence regulation pathway and contributes to understanding the complex association between V. cholerae virulence and QS signals. This evidence furnishes new insights for future studies on cholerae's pathogenic mechanisms.

Targeting microbial quorum sensing: the next frontier to hinder bacterial driven gastrointestinal infections

Bacteria synchronize social behaviors via a cell-cell communication and interaction mechanism termed as quorum sensing (QS). QS has been extensively studied in monocultures and proved to be intensively involved in bacterial virulence and infection. Despite the role QS plays in pathogens during laboratory engineered infections has been proved, the potential functions of QS related to pathogenesis in context of microbial consortia remain poorly understood. In this review, we summarize the basic molecular mechanisms of QS, primarily focusing on pathogenic microbes driving gastrointestinal (GI) infections. We further discuss how GI pathogens disequilibrate the homeostasis of the indigenous microbial consortia, rebuild a realm dominated by pathogens, and interact with host under worsening infectious conditions via pathogen-biased QS signaling. Additionally, we present recent applications and main challenges of manipulating QS network in microbial consortia with the goal of better understanding GI bacterial sociality and facilitating novel therapies targeting bacterial infections.

Effect of LuxS/AI-2-mediated quorum sensing system on bacteriocin production of Lactobacillus plantarum NMD-17

Lactobacillus plantarum NMD-17 separated from koumiss could produce a bacteriocin named plantaricin MX against Gram-positive bacteria and Gram-negative bacteria. The bacteriocin synthesis of L. plantarum NMD-17 was remarkably induced in co-cultivation with Lactobacillus reuteri NMD-86 as the increase of cell numbers and AI-2 activity, and the expressions of luxS encoding signal AI-2 synthetase, plnB encoding histidine protein kinase, plnD encoding response regulator, and plnE and plnF encoding structural genes of bacteriocin were significantly upregulated in co-cultivation, showing that the bacteriocin synthesis of L. plantarum NMD-17 in co-cultivation may be regulated by LuxS/AI-2-mediated quorum sensing system. In order to further demonstrate the role of LuxS/AI-2-mediated quorum sensing system in the bacteriocin synthesis of L. plantarum NMD-17, plasmids pUC18 and pMD18-T simple were used as the skeleton to construct the suicide plasmids pUC18-UF-tet-DF and pMD18-T simple-plnB-tet-plnD for luxS and plnB-plnD gene deletion, respectively. luxS and plnB-plnD gene knockout mutants were successfully obtained by homologous recombination. luxS gene knockout mutant lost its AI-2 synthesis ability, suggesting that LuxS protein encoded by luxS gene is key enzyme for AI-2 synthesis. plnB-plnD gene knockout mutant lost the ability to synthesize bacteriocin against Salmonella typhimurium ATCC14028, indicating that plnB-plnD gene was a necessary gene for bacteriocin synthesis of L. plantarum NMD-17. Bacteriocin synthesis, cell numbers, and AI-2 activity of luxS or plnB-plnD gene knockout mutants in co-cultivation with L. reuteri NMD-86 were obviously lower than those of wild-type strain in co-cultivation at 6-9 h (P < 0.01). The results showed that LuxS/AI-2-mediated quorum sensing system played an important role in the bacteriocin synthesis of L. plantarum NMD-17 in co-cultivation.

iTRAQ-based quantitative proteomic analysis of the antibacterial mechanism of silver nanoparticles against multidrug-resistant Streptococcus suis

Background

The increase in antibiotic resistance of bacteria has become a major concern in clinical treatment. Silver nanoparticles (AgNPs) have significant antibacterial effects against Streptococcus suis. Therefore, this study aimed to investigate the antibacterial activity and mechanism of action of AgNPs against multidrug-resistant S. suis.

Methods

The effect of AgNPs on the morphology of multidrug-resistant S. suis was observed using scanning electron microscopy (SEM). Differentially expressed proteins were analyzed by iTRAQ quantitative proteomics, and the production of reactive oxygen species (ROS) was assayed by H2DCF-DA staining.

Results

SEM showed that AgNPs disrupted the normal morphology of multidrug-resistant S. suis and the integrity of the biofilm structure. Quantitative proteomic analysis revealed that a large number of cell wall synthesis-related proteins, such as penicillin-binding protein and some cell cycle proteins, such as the cell division protein FtsZ and chromosomal replication initiator protein DnaA, were downregulated after treatment with 25 μg/mL AgNPs. Significant changes were also observed in the expression of the antioxidant enzymes glutathione reductase, alkyl hydroperoxides-like protein, α/β superfamily hydrolases/acyltransferases, and glutathione disulfide reductases. ROS production in S. suis positively correlated with AgNP concentration.

Conclusion

The potential antibacterial mechanism of AgNPs may involve disrupting the normal morphology of bacteria by inhibiting the synthesis of cell wall peptidoglycans and inhibiting the growth of bacteria by inhibiting the cell division protein FtsZ and Chromosomal replication initiator protein DnaA. High oxidative stress may be a significant cause of bacterial death. The potential mechanism by which AgNPs inhibit S. suis biofilm formation may involve affecting bacterial adhesion and interfering with the quorum sensing system.

Roles and regulation of quorum sensing in anaerobic granular sludge: Research status, challenges, and perspectives

Anaerobic granular sludge (AnGS) has a complex and important internal microbial communication system due to its unique microbial layered structure. As a concentration-dependent communication system between bacterial cells through signal molecules, QS (quorum sensing) is widespread in AnGS and exhibits great potential to regulate microbial behaviors. Therefore, the universal functions of QS in AnGS have been systematically summarized in this paper, including the influence on the metabolic activity, physicochemical properties, and microbial community of AnGS. Subsequently, the common QS-based AnGS regulation approaches are reviewed and analyzed comprehensively. The regulation mechanism of QS in AnGS is analyzed from two systems of single bacterium and mixed bacteria. This review can provide a comprehensive understanding of QS functions in AnGS systems, and promote the practical application of QS-based strategies in optimization of AnGS treatment process.

Construction of stable microbial consortia for effective biochemical synthesis

Microbial consortia can complete otherwise arduous tasks through the cooperation of multiple microbial species. This concept has been applied to produce commodity chemicals, natural products, and biofuels. However, metabolite incompatibility and growth competition can make the microbial composition unstable, and fluctuating microbial populations reduce the efficiency of chemical production. Thus, controlling the populations and regulating the complex interactions between different strains are challenges in constructing stable microbial consortia. This Review discusses advances in synthetic biology and metabolic engineering to control social interactions within microbial cocultures, including substrate separation, byproduct elimination, crossfeeding, and quorum-sensing circuit design. Additionally, this Review addresses interdisciplinary strategies to improve the stability of microbial consortia and provides design principles for microbial consortia to enhance chemical production.