Aeromonas veronii is a pathogen that is widely found in aquaculture environments. It has been observed to colonize the gastrointestinal tract of fish and other aquatic animals, with the potential to cause severe infections. Previous studies have demonstrated that probiotics, such as Lactococcus lactis 01, Lactococcus lactis 02, Enterococcus pseudoavium 03, and Bacillus sp. 04, can reduce the colonization capability of A. veronii. In this study, we sought to ascertain whether these four probiotics could affect chemotaxis by interfering with N-acyl-homoserine lactones (AHLs), thereby regulating the intestinal colonization ability of A. veronii. The findings of this study demonstrate that the extracts of L. lactis 01, L. lactis 02, and E. pseudoavium 03 significantly attenuate the chemotactic behavior of A. veronii. It is noteworthy that L. lactis 01 exhibited a substantial capacity to impede A. veronii from producing AHLs, and a preliminary investigation into substances capable of inhibiting L. lactis 01. Furthermore, we observed that L. lactis 01 can ameliorate inflammation and oxidative stress induced by A. veronii colonization in the intestinal tract of loaches. Furthermore, genome analysis of L. lactis 01 confirmed that this strain is safe for practical application. These findings lay the foundation for further research into the molecular mechanisms underlying the interactions between probiotics and pathogens, offering novel perspectives for the development of probiotic-based biocontrol strategies.

Bacterial community dynamics underlie ecosystem functioning in river networks, yet how different bacterial lifestyles respond to bottom-up biotic drivers under confluence-induced hydraulics remains unclear. Here, we quantified spatial heterogeneity in free-living (FL), particle-associated (PA) and sedimentary (S) bacterial assemblages, coupled with phytoplankton and extracellular enzyme profiles, at the Yellow River-Fenhe River confluence during the summer wet season. Clear habitat partitioning emerged, with stronger divergence at the water-sediment interface than between the two planktonic fractions (FL vs. PA). Hydrological source tracking showed that Fenhe River-derived taxa dominated both water and sediment within the confluence reaches, whereas Yellow River lineages prevailed in the downstream reaches. Community assembly shifted hierarchically: homogeneous selection dominated FL assemblages but declined progressively toward PA and sedimentary fractions, while dispersal limitation intensified in tandem with niche contraction. Multivariate analyses showed that in addition to physicochemical factors, enzyme activity is the strongest factor predicting FL communities, explaining 43.6% of variability, whereas the phytoplankton community best predicted PA communities (68.8%). Sedimentary communities correlated weakly with phytoplankton associations (21.8%) and showed no significant link with enzyme activity. Our findings identify phytoplankton communities and enzymatic potential as key bottom-up drivers whose relative importance varies with bacterial lifestyle, providing mechanistic insight into biophysical dynamics within river-confluence ecosystems.

A novel polysaccharide-degrading bacterial strain, designated ASW11-125T, was isolated from intertidal sediments in Aoshan Bay, Qingdao, China. The strain was strictly aerobic, Gram-stain-negative, catalase-positive but oxidase-negative, short rod-shaped, and exhibited gliding motility without flagella. Growth occurred at 4–35°C (optimum 28°C), pH 6.0–8.0 (optimum pH 7.0), and in 0.5–16.0

Bacteriophages and bacteria engage in an ancient evolutionary arms race that drives molecular innovation and genetic diversification. Bacteria evolve resistance mechanisms while phages counter with escape mutations, generating diverse defense and counter-defense systems. Within this evolutionary framework, horizontal gene transfer (HGT) enables bacteria to acquire immune mechanisms and repurpose phage-derived elements into host-beneficial functions. Here, we report the characterization of Eliminase (ElmA), a chimeric enzyme in Escherichia coli O10:K5(L):H4 that exemplifies this evolutionary strategy by converting phage weaponry into a bacterial shield. Through integrated phylogenetic, structural, and functional analyses, we demonstrate that ElmA originated from recombination between bacteriophage K5A's tailspike lyase KflA and tail fiber domains-a previously undocumented mechanism generating a host-beneficial capsular regulator from phage lytic machinery. Genomic island analysis positioned elmA within a prophage-derived genetic cassette, while sequence comparisons revealed high similarity between ElmA's N-terminal region and phage tail fiber proteins. Isothermal titration calorimetry demonstrated that the N-terminal domain binds heparosan with Kd of 37.8 μM, accommodating approximately five disaccharide units per protein molecule. Substrate specificity analysis revealed ElmA exhibits strict preference for heparosan, with activity dramatically reduced by N-position modifications. Functional characterization using ElmA-deficient and overexpressing strains revealed a novel regulatory role in capsular polysaccharide trafficking. ElmA facilitates export of low molecular weight heparosan fragments while controlling capsular thickness, functioning as a molecular rheostat modulating polysaccharide flux. These findings illuminate how bacteria co-opt phage-derived enzymes to create sophisticated regulatory systems, transforming viral lytic machinery into host-beneficial functions.

Antimicrobial resistance (AMR) in aquatic ecosystems is an escalating One Health concern. However, viable antibiotic-resistant bacteria (ARB)-particularly pathogenic strains-and their mobility remain poorly characterized at hydrological interfaces such as river confluences. Here, we integrated culture enrichment, high-throughput 16S rRNA gene sequencing, isolate phenotyping and whole-genome analysis to profile ARB and antibiotic-resistant bacterial pathogens (ARBPs) in sediments from the Fenhe River-Yellow River confluence. Non-selective enrichment reduced community complexity yet uniquely recovered dozens of rare taxa absent from direct sequencing. Antibiotic enrichment induced pronounced, drug-specific ARB shifts; antibiotic type explained more variance (19.3%) than hydrological region (11.2%). Pathogen signals were strongly amplified by enrichment, and ARBP communities retained significant regional clustering. Notably, the confluence hydrodynamic region (CHR) consistently exhibited the highest ARBP richness. Of the 121 recovered isolates, 94.2% were phenotypically resistant and 73.5% were multidrug-resistant; 89.3% matched in situ ASVs, bridging community profiles and cultivable strains. We recovered seven high-risk multidrug-resistant pathogens (belonging to Pseudomonas, Acinetobacter, Aeromonas) as viable isolates, even though they were rare or undetected by direct sequencing. Whole-genome sequencing revealed 658 virulence factors and 312 antibiotic-resistance genes (ARGs). Clinically relevant determinants (e.g., AAC(6')-Iaa, OXA-917, OprN) were embedded within mobile genetic elements, including transposons, plasmid-like contigs, and integrative and conjugative elements (ICEs). The edeine acetyltransferase gene edeQ showed 100% nucleotide identity to alleles from clinical sources, indicating overlap between environmental and clinical resistomes. Collectively, our findings highlight river confluences as priority surveillance nodes and demonstrate that culture-enriched sequencing more effectively quantifies viable AMR hazards than sequencing alone.

Aeromonas veronii is widely distributed in aquatic environments, as well as in a variety of aquatic products, poultry, and other meat products. As a typical zoonotic pathogen, it not only directly infects hosts and threatens their health, but also disseminates through the food chain. The prevention and control of A. veronii, particularly food contamination caused by this pathogen, remains a critical concern, necessitating the development of novel control strategies. Therefore, this study explores the antibacterial efficacy and underlying mechanisms of geranic acid against A. veronii, alongside its practical application in inhibiting bacterial proliferation in marinated beef and perch. Geranic acid exhibited antibacterial activity against various bacterial species, after treatment with geranic acid, the levels of reactive oxygen species (ROS), malondialdehyde (MDA) content, superoxide dismutase (SOD) activity and catalase (CAT) activity of A. veronii were significantly increased, indicating that geranic acid can induce oxidative stress and increase cell membrane permeability, thereby resulting in cell damage and even death. Geranic acid also reduced extracellular protease activity, inhibited early biofilm formation, and interfered with quorum sensing, thus weakening the swarming motility and consequently decreasing the virulence of A. veronii. The application of a relatively high concentration of geranic acid in meat products significantly reduced the total bacterial counts and Aeromonas counts, and improved meat quality to a certain extent. These findings suggest that geranic acid, as an antibacterial agent, has important application potential in controlling microbial contamination of meat products.

Heparin is a critically important clinical anticoagulant. The biosynthesis of heparin using Escherichia coli-based multienzyme cascades represents a promising alternative to animal-derived production. However, efficient deployment of heparin-synthesizing enzymes faces significant challenges, particularly in achieving recombinant expression of functionally active heparin N-deacetylase/N-sulfotransferase (NDST) enzymes in bacterial systems. In this article, we implement a strategy termed model animal-guided sequence-structure-activity to discover functional NDST orthologs compatible with prokaryotic expression. Coupled with computationally assisted focused rational iterative site-specific mutagenesis, we engineered the high-performance variant NDST-M8, which exhibited a 10.65-fold increase in activity and a 3.84-fold improvement in stability relative to the truncated variant AgNDST-M0. This methodology enabled an E. coli multienzyme cascade that synthesizes bioactive heparin from heparosan backbones, with tunable N-sulfation levels (30-90%) that precisely modulate anticoagulant activity. Our work resolves critical bottlenecks in enzymatic heparin production, establishing a scalable, nonanimal platform for the industrial manufacturing of activity-graded heparin therapeutics.

Plant growth-promoting bacteria (PGPB) can enhance phytoremediation, but whether inoculation alters rhizosphere microbial abundance and elicits tissue-specific endophytic responses remains unclear. Here, Enterobacter sp. was applied to improve Mn/Cd phytoextraction by Polygonum lapathifolium L. Inoculation decreased rhizosphere pH and increased acid-extractable Mn and Cd by 11.8% and 45.5%, respectively, accompanied by enhanced nutrient availability and C, N and P cycling enzyme activities. It also altered rhizosphere bacterial and fungal community structure, increased their absolute abundances and functional potential, and markedly increased rhizosphere Enterobacter abundance. In parallel, inoculation induced adaptive shifts in plant endophytic microbial communities, as reflected by higher root bacterial community-level rrn copy numbers but lower values in leaves, together with enhanced modularity of the endophytic interaction network under the C1.0 (9.50 ×1010 CFU/pot) treatment, predominated by Pseudomonadota and Actinomycetota. Path analysis revealed that rhizosphere bacteria indirectly promoted Mn/Cd phytoextraction by regulating soil properties, while alleviation of oxidative stress sustained metal uptake. Inoculation reduced H2O2 and ·O2- levels, enhanced antioxidant capacity, and increased plant growth and metal accumulation. Overall, Enterobacter sp. inoculation enhanced phytoextraction through quantitative and compositional changes in rhizosphere microbiota, tissue-specific endophytic responses, and improved plant stress tolerance, supporting its application in Mn-Cd contaminated soils.

Staphylococcus aureus, a high-risk bacterial pathogen, poses significant threats to human health through the aquaculture chain. However, the mechanisms underlying the use of probiotics to prevent and control S. aureus infections in aquatic animals remain insufficiently explored and warrant further investigation. Here, we systematically investigated the anti-S. aureus effects of Bacillus velezensis PPB05 and its potential benefits as a fish feed additive. Our findings indicated that strain PPB05 exhibited potential inhibitory activity against S. aureus by secreting non-proteinaceous antibacterial substances that are thermostable, pH-stable, and protease-resistant. Additionally, strain PPB05 showed capacity to disrupt S. aureus biofilm formation and exhibited promise in clearing mature biofilms. In a loach model, strain PPB05 attenuated intestinal colonization of S. aureus and exhibited potential in protecting the intestinal barrier, improving intestinal permeability, and enhancing antioxidant capacity. Dietary supplement of strain PPB05 promoted the growth performance and survival rates of loaches after S. aureus infection. These findings contribute to the exploration of an environmentally friendly and efficient alternative strategy for controlling S. aureus infections in aquatic animals.

Hafnia paralvei, as an important foodborne pathogen with a strong ability to form biofilms, will cause food to spoil and deteriorate, thereby seriously threatening food safety. However, the mechanism of the quorum sensing (QS) system in the biofilm formation and spoilage process of H. paralvei has not been fully characterized. Here, we explored the positive regulatory effects of two types of QS system on H. paralvei Z11 biofilm formation, which further investigated their promoting effects on the spoilage of crucian carp. The results showed that overexpression of expI significantly increased the production of N-acyl-homoserine lactones (AHLs), and overexpression of luxS significantly increased the yield of autoinducer-2 (AI-2). Additionally, AHLs and AI-2-mediated QS promoted the synthesis of cyclic diguanylate monophosphate (c-di-GMP), thereby increasing the level of biofilm formation. The effects of biofilm formation mediated by AHLs and AI-2 on the meat quality and spoilage of crucian carp were determined, which found that the elevated biofilm formation significantly lowered the meat quality and promoted the spoilage potential of H. paralvei on crucian carp, simultaneously affecting the structure of meat microbiota and increasing the abundance of spoilage-associated bacteria. This research provides a theoretical foundation for further understanding the potential role of bacterial QS system mediated biofilm formation in food spoilage.

The initial variations in soil bacteria at the very beginning of reclamation still remains unclear. This study investigates the impact on bacterial communities of eight different treatments, including uncultivated land, unfertilized cultivation, chemical fertilizer, chemical fertilizer + bacterial fertilizer, manure, manure + bacterial fertilizer, manure + chemical fertilizer, and manure + chemical fertilizer + bacterial fertilizer, during the short-term reclamation of coal-mining soils. The results showed that total nitrogen, available phosphorus, soil organic carbon, microbial biomass carbon, and alkaline phosphatase activity were significantly increased in all fertilization treatments compared to uncultivated land (p < 0.05). All fertilization treatments other than chemical fertilizer harbored significantly higher activities of urease, catalase, and invertase than unfertilized cultivation (p < 0.05). The bacterial communities structures in manure-amended treatments significantly differed in uncultivated land and unfertilized cultivation and were phylotypically shifted from oligotrophic to Actinobacteria-dominant copiotrophic traits, accompanied with phenotypic succession of the enriching characteristics of Gram-positive, biofilms formation, and stress tolerance. The co-occurrence network in manure-amended treatments harbored a simple co-occurrence network, indicating more productive soils than in no-manure treatments. Manure amendment, total nitrogen, microbial biomass carbon, invertase, catalase, and soil moisture were the key driving factors. Our study underscores the bacterial initialization characteristics promoted by manure at the very beginning of coal-mining reclamation.

The formation of biofilm by pathogen promotes its colonization, posing significant threats to the environment and the health of humans and animals. The mechanism by which c-di-GMP regulates biofilm formation and its impact on pathogen colonization and intestinal injury has not been fully characterized. Here, we found that overexpressing the phosphodiesterases encoding gene adrB in Hafnia paralvei Z11 reduced c-di-GMP levels, leading to a decrease in outer membrane proteins (OMPs) content and the declining adhesion, as well as a lower level of biofilm formation. Conversely, overexpressing the OMPs-encoding gene lapA significantly enhanced adhesion and biofilm formation. Furthermore, overexpression of adrB exhibited a lower colonization ability in the loach intestine, whereas overexpression of lapA in strain Z11::pBBR1MCS-adrB adrB significantly promoted its colonization in the loach intestine, and caused damage to intestinal barrier integrity, inducing host oxidative stress and the elevated expression level of inflammation-related genes. Thus, this study reveals that c-di-GMP regulates lapA-mediated biofilm formation of H. paralvei Z11, which promotes its intestinal colonization and damage to loach intestines, enhancing our understanding of pathogen-induced intestinal colonization and damage strategies.

3'-Phosphoadenosine-5'-phosphosulfate (PAPS), a universal sulfate donor for sulfation reactions, is indispensable for synthesizing bioactive molecules including therapeutic glycosaminoglycans and sulfolipids; however, its enzymatic production on an industrial scale is constrained by ATP overconsumption and the limited free enzyme reusability. We report an integrated biocatalytic platform combining ATP regeneration with affinity immobilization to enable sustainable PAPS biosynthesis. A polyphosphate kinase-driven ATP regeneration system achieved 86% PAPS conversion efficiency by regenerating ADP using low-cost polyphosphate. Biotin-streptavidin affinity immobilization enhanced operational stability, retaining >50% activity over six reuse cycles with a cumulative PAPS titer of 12.02 g/L. Coupling adenosine-converting Saccharomyces cerevisiae whole-cell catalysts with this system decreased substrate costs by 80.7% and delivered 96% molar PAPS yield from adenosine. This work provides a sustainable platform for industrial PAPS biosynthesis to promote sulfated biomolecule production, including glycosaminoglycans and other therapeutics.

Rapid advances in synthetic biology are driving the development of microbes as therapeutic agents. While the immunosuppressive tumor microenvironment creates a favorable niche for the systematic delivery of bacteria and therapeutic payloads, these can be harmful if released into healthy tissues. To address this limitation, we designed a spatiotemporal targeting system for engineered Escherichia coli Nissle 1917, controlled by azide-modified hyaluronic acid hydrogel and near-infrared radiation induction. Using a temperature-driven genetic status switch, the system produced durable therapeutic output and promoted the therapeutic activity in solid tumors. The combination of azide-modified hyaluronic acid hydrogel and temperature-sensitive, engineered Escherichia coli Nissle 1917 provided spatiotemporal targeting of solid tumors, not only showing significant therapeutic effects on primary solid tumors, but also inhibiting the metastasis and recurrence of cancer cells by enhancing tumor-infiltrating lymphocytes. This system has potential for clinical application.

Three Gram-stain-negative, aerobic, rod-shaped bacterial strains, FR7-31 T, FR7-34 and HH7-4, were isolated from sediment samples of the Fenhe River basin, China. The 16S rRNA gene sequence analysis revealed that strain FR7-31 T shares 99.7

Petroleum-associated water harbors diverse microbial communities, including hydrocarbon-degrading bacteria, sulfate-reducing bacteria, and methanogenic archaea. The growth and metabolism of these organisms, as well as their community composition, can affect various aspects of oil field development and oil produced water treatment. In this study, Illumina-based 16S rRNA gene sequencing was used to analyze the microbial community structures of oilfield produced water processed at two treatment stations and subjected to different treatment protocols. Significant differences in microbial community α-diversity and richness resulted from the different treatment protocols. The treatment of oil produced water effectively reduced the oil content, accompanied by the a reduction in Desulfobacterota. Proteobacteria was the dominant phylum in oil produced water; its core presence, along with Patescibacteria and Desulfobacterota, was identified in a co-occurrence network analysis of the microbial community. Redundancy analysis showed significant positive correlations between microbial community diversity and the oil and suspended solids contents of the oil produced water, highlighting the role of treatment protocols in shaping both microbial composition and water characteristics. Thus, this study provides potential insights into the processes of souring in oil fields and contributes to the theoretical understanding of oil-produced water treatment, which may inform future optimization of treatment protocols.

ABSTRACT Quorum sensing systems, particularly autoinducer-2 (AI-2) signaling, have significant effects on bacterial colonization and virulence. However, how they affect intestinal colonization by pathogens and subsequent host immune responses remains unclear. Here, we investigated the influence of AI-2 signaling on the intestinal colonization ability of Aeromonas veronii Z12 and the host’s immune response. We found that AI-2 signaling promoted the colonization of A. veronii to the intestine of loach ( Misgurnus anguillicaudatus ) and caused severe intestinal damage, while D-ribose, an AI-2 signaling inhibitor, effectively inhibited the colonization of A. veronii . Transcriptomic sequencing elucidated the molecular mechanism of this damage, revealing upregulation of p53 pathway genes associated with apoptosis. Furthermore, intestinal microbiota dysbiosis induced by A. veronii colonization was associated with host cell apoptosis, leading to nitrite accumulation, which increased intracellular reactive oxygen species (ROS) levels, which activated the p53 pathway, and induction of cell apoptosis. These findings provide insights into the interaction among bacterial quorum sensing, intestinal microbiota, and the host immune response, which highlight potential therapeutic targets for mitigating bacterial-induced intestinal damage. IMPORTANCE The intestinal colonization of pathogens regulated by autoinducer-2 (AI-2) signaling and its induced host response have not been fully characterized. Here, we revealed the effect of AI-2 on intestinal colonization of Aeromonas veronii and its induced cell apoptosis in loach. Our study demonstrated that the deficiency of AI-2 significantly reduced A. veronii colonization in the loach intestine and mitigated the tissue damage. Additionally, A. veronii colonization induced significant upregulation of p53 pathway genes and proteins, indicating a key role of AI-2 signaling in host responses. Understanding these mechanisms not only helps to elucidate the pathogenicity of A. veronii but also may provide broader insights into the pathogenic mechanisms of other pathogens, thus revealing general principles of pathogen–host interactions across different models. Furthermore, we found that A. veronii colonization led to intestinal microbiota dysbiosis, notably an increase in the abundance of Hypomicrobium sp., which was associated with nitrite accumulation, elevating reactive oxygen species levels, activating the p53 pathway, and inducing cell apoptosis. These findings provide important insights into the complex mechanisms of AI-2 signaling in bacterial–host interactions. Additionally, the regulatory role of AI-2 signaling may have potential clinical applications as an intervention strategy, offering new directions for developing treatments against intestinal infections.

Background: Nicotinic acid dehydrogenase possesses the capability to convert nicotinic acid into 6hydroxynicotinic acid, a compound of significant research value as a pharmaceutical intermediate. The extraction of nicotinic acid dehydrogenase is primarily performed by strains. However, the enzyme activity of the strains reported currently is relatively low, and their potential to catalyze the production of 6hydroxynicotinic acid is insufficient to meet industrial requirements. Results: Due to the revealing properties of 6-hydroxynicotinic acid, this study proposes a technique for calculating the luminescence intensity of colonies, which is based on a fluorescence spectrometer. The developed method establishes a reliable linear relationship (88.2%) between the luminescence intensity and enzyme activity. Consequently, it has been employed to screen strains that produce nicotinate dehydrogenase. This screening approach allows for the evaluation of about 500 enzyme-producing strains daily, presenting an efficient strategy for screening. Conclusions: Through this app drogenase, Pseudomonas poae tion, it was utilized to produc meeting the requirements for in its application for strain sc How to cite: Li Y, Tang J, Xin Pseudomonas poae. Electron J (c) 2025 The Authors. Publishe This is an open access article u roach, a novel high enzyme activity strain producing nicotinic acid dehyhave been obtained, which is designated as HD530. After process optimizae 6-hydroxynicotinic acid, achieving a high yield of 155.45 g/L within 72 h, industrial production. The effectiveness and potential of this technique lie reening and improvement. K, et al. Efficient production of 6-hydroxynicotinic acid by newly isolated Biotechnol 2025;75. https://doi.org/10.1016/j.ejbt.2025.01.002. d by Elsevier Inc. on behalf of Pontificia Universidad Cat & oacute;lica de Valparaiso. nder the CC BY-NC-ND license (http://creativecommons.org/licenses/by-ncnd/4.0/).

Aeromonas veronii, a zoonotic opportunistic pathogen, has posed serious threats to both the aquaculture industry and human health. The quorum sensing (QS) system plays a crucial regulatory role in the expression of virulence factors in A. veronii. Quorum sensing inhibitors (QSIs) provide an alternative control method by disrupting bacterial QS-systems, thereby reducing pathogenicity and virulence without directly killing bacteria. This study primarily explored the interference effect of Priestia sp. PPB30 on the LuxS/AI-2 QS system of A. veronii Z12 and its impact on virulence factors. Screening through a bioluminescence assay revealed that strain PPB30 effectively reduced the levels of autoinducer-2 (AI-2) in A. veronii Z12 without affecting its growth. Following treatment with strain PPB30, significant changes in the expression of LuxS/AI-2 related genes in strain Z12 were observed, along with a reduction in biofilm formation and the expression of virulence factors, including adhesion, hemolysis, extracellular proteases, and motility. Moreover, strain PPB30 reduced the colonization of A. veronii Z12 in the intestines of loaches, but had no inhibitory effect on the colonization level of the LuxS/AI-2 system-deficient mutant strain Z12ΔluxS in the loach intestine. Additionally, we found that dietary supplementation with strain PPB30 effectively alleviated intestinal damage caused by A. veronii Z12 infection and mitigated the host' s inflammatory response. The research findings reveal that Priestia sp. PPB30, as a potential probiotic, offers a novel strategy for the prevention and control of aquaculture pathogens by disrupting the LuxS/AI-2 QS-system, thereby inhibiting the expression of virulence and intestinal colonization of A. veronii Z12.

Aeromonas veronii is one of the most common major pathogens in aquaculture, which can infect aquatic animals and cause significant economic losses. Quorum sensing (QS) of A. veronii promotes its intestinal colonization through regulating the production of virulence factors, but little is known about the effects of QS systems on the gonadal colonization of A. veronii. In this study, transcriptomic analysis of intestinal tissues in loaches after infection with A. veronii revealed the enrichment of reproductive-related genes between the wild strain A. veronii Z12 and the QS deficient mutant strain Z12ΔluxS treatment groups. The results indicated that A. veronii might colonize the gonads of loaches and cause damage through an autoinducer-2 (AI-2) mediated-QS mechanism. Through quantitative analysis of intestinal permeability and tight junction protein-related genes, it was found that A. veronii could break through the intestinal barrier. Furthermore, fluorescence signal detection revealed that A. veronii entered and colonized the gonads through the bloodstream. Analysis of gonadal tissue sections showed that A. veronii infection caused tissue lesions and induced apoptosis, resulting in damage to the gonads. The estradiol-testosterone (E2/T) ratio was disturbed, as indicated by the detection of sex hormone levels, which further demonstrating the damage caused by A. veronii infection on the reproductive ability of loaches. This study provides new insights into the promotional impact of the AI-2 mediated QS system on the toxic effects of A. veronii to the reproductive capacity of loach, which is crucial for the healthy cultivation of aquatic organisms.