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Boron is an essential element for autoinducer-2 (AI-2) synthesis of quorum sensing (QS) system, which affects bacterial collective behavior. As a living biocatalyst, biofilms can stably catalyze the activity of intracellular enzymes. However, it is unclear how boron affects biofilm formation in E. coli, particularly recombinant E. coli with intracellular enzymes. This study screened different boron derivatives to explore their effect on biofilm formation. The stress response of biofilm formation to boron was illuminated by analyzing AI-2 activity, extracellular polymeric substances (EPS) composition, gene expression levels, etc. Results showed that boron derivatives promote AI-2 activity in QS system. After treatment with H3BO3 (0.6 mM), the AI-2 activity increased by 65.99%, while boron derivatives increased the biomass biofilms in the order H3BO3 > NaBO2 > Na2B4O7 > NaBO3. Moreover, treatment with H3BO3 (0.6 mM) increased biomass by 88.54%. Meanwhile, AI-2 activity had a linear correlation with polysaccharides and protein of EPS at 0–0.6 mM H3BO3 and NaBO2 (R2 > 0.8). Furthermore, H3BO3 upregulated the expression levels of biofilm formation genes, quorum sensing genes, and flagellar movement genes. These findings demonstrated that boron promoted biofilm formation by upregulating the expression levels of biofilm-related genes, improving the QS system AI-2 activity, and increasing EPS secretion in E. coli.

Background Human health is seriously threatened by antibiotic-induced intestinal disorders. Herein, we aimed to determine the effects of Autoinducer-2 (AI-2) combined with Lactobacillus rhamnosus GG ( LGG ) on the intestinal barrier function of antibiotic-induced intestinal dysbiosis neonatal mice. Methods An antibiotic-induced intestinal dysbiosis neonatal mouse model was created using antibiotic cocktails, and the model mice were randomized into the control, AI-2, LGG , and LGG  + AI-2 groups. Intestinal short-chain fatty acids and AI-2 concentrations were detected by mass spectrometry and chemiluminescence, respectively. The community composition of the gut microbiota was analyzed using 16S rDNA sequencing, and biofilm thickness and bacterial adhesion in the colon were assessed using scanning electron microscopy. Transcriptome RNA sequencing of intestinal tissues was performed, and the mRNA and protein levels of HCAR2 (hydroxycarboxylic acid receptor 2), claudin3, and claudin4 in intestinal tissues were determined using quantitative real-time reverse transcription PCR and western blotting. The levels of inflammatory factors in intestinal tissues were evaluated using enzyme-linked immunosorbent assays (ELISAs). D-ribose, an inhibitor of AI-2, was used to treat Caco-2 cells in vitro. Results Compared with the control, AI-2, and LGG groups, the LGG  + AI-2 group showed increased levels of intestinal AI-2 and proportions of Firmicutes and Lacticaseibacillus , but a reduced fraction of Proteobacteria . Specifically, the LGG  + AI-2 group had considerably more biofilms and LGG on the colon surface than those of other three groups. Meanwhile, the combination of AI-2 and LGG markedly increased the concentration of butyric acid and promoted Hcar2, claudin3 and claudin4 expression levels compared with supplementation with LGG or AI-2 alone. The ELISAs revealed a significantly higher tumor necrosis factor alpha (TNF-α) level in the control group than in the LGG and LGG  + AI-2 groups, whereas the interleukin 10 (IL-10) level was significantly higher in the LGG  + AI-2 group than in the other three groups. In vitro, D-ribose treatment dramatically suppressed the increased levels of Hcar2, claudin3, and claudin4 in Caco-2 cells induced by AI-2 +  LGG . Conclusions AI-2 promotes the colonization of LGG and biofilm formation to improve intestinal barrier function in an antibiotic-induced intestinal dysbiosis neonatal mouse model.

Objective: The objective of this study was to investigate the effects of dietary D-ribose supplementation on the growth performance, nutrient digestibility, serum biochemistry, rumen fermentation characteristics, and microbial LuxS/autoinducer-2 (AI-2) quorum sensing in Hu sheep.Methods: Eighteen female Hu sheep, aged 3 months with similar body weights (20.47±0.58 kg), were randomly divided into two groups of nine animals each. The control group was fed a basal diet (CON), while the experimental group received the basal diet supplemented with 300 mg/kg of D-ribose (DR). After 80 days of individual pen feeding, blood, rumen fluid, and fecal samples were collected for analysis.Results: The results showed that the average daily gain was higher in the DR group than in the CON group, and the feed-to-gain ratio was lower in the DR group (p<0.05). The apparent digestibility of ether extract tended to be higher in the DR group (p = 0.068). In comparison to the CON group, the levels of serum cortisol, malondialdehyde, and reactive oxygen species were lower in the DR group, while superoxide dismutase and glutathione peroxidase levels were higher, resulting in a decreased oxidative stress index (p<0.05). The rumen pH and microbial protein concentration were higher in the DR group (p<0.05), and no differences in ammonia nitrogen and volatile fatty acids concentrations were observed between the CON and DR groups (p>0.10). The rumen microbial density was higher in the DR group, while the concentrations of AI-2 signaling molecule, biofilm formation, and exopolysaccharides were lower (p<0.05).Conclusion: The findings of this study indicate that dietary supplementation with D-ribose can enhance the growth performance, improve serum antioxidant capacity, and inhibit rumen microbial LuxS/AI-2 quorum sensing in Hu sheep.

Quorum sensing (QS) is a chemical communication process that connects microbial members in various microbial systems. Bacterial communication networks mediated by QS play important roles in the regulation of intestinal microecological balance as well as nutrition and metabolism of the host. However, how human gut microbes utilize QS signals to communicate with one another remains largely unknown. In this study, we first examined the prevalence and abundance of genes encoding QS signal synthases in 3329 species representatives clustered from 289232 prokaryotic genomes in the Unified Human Gastrointestinal Genome collection. Our results show autoinducer-2 (AI-2) is the most prevalent QS signal within the human gut microbiota, with the synthase gene luxS being found in 2039 species mainly distributed within Firmicutes, Actinobacteriota, Bacteroidota, and Proteobacteria. Furthermore, 299 species carry genes encoding one or more types of AI-2 receptors (LuxP-, LsrB-, dCache_1-, and GAPES1-type). The dCache_1- and GAPES1-type receptors can function as methyl-accepting chemotaxis proteins, histidine kinases, c-di-GMP synthases and/or c-di-GMP-specific phosphodiesterases, serine phosphatases, and serine/threonine kinases, suggesting the diversity of AI-2-mediated interspecies communication modes among human gut microbiota. Metatranscriptomic analysis showed that a number of AI-2 synthase- and receptor-encoding genes can be expressed in the human gut in healthy and/or unhealthy states. The communication network analysis suggests that AI-2-mediated interactions widely occur among members of Firmicutes, Proteobacteria, Actinobacteriota, Campylobacterota, and Spirochaetota. Overall, this study deepens understanding of QS-mediated communication network among human gut microbiota, and provides guidance for engineering gut microbiota and constructing new synthetic microbial consortia based on complex microbial interactions.

The QS signal AI-2 is widely synthesized in bacteria and has been implicated in the regulation of numerous bacterial group behaviors. However, in contrast to the wide distribution of this signal, its receptors have only been found in a small number of bacterial species, and the underlying mechanisms for the detection of and response to AI-2 remain elusive in most bacteria. It is worth noting that the periplasmic protein LuxP is the uniquely identified receptor for AI-2 in Vibrio spp. Here, we identify a second type of AI-2 receptor, a membrane-bound histidine kinase with a periplasmic dCache_1 sensory domain, in a member of the genus Vibrio , and thus show that AI-2 enhances the defense of V. furnissii against oxidative stress and DNA damage by modulation of c-di-GMP signaling via the AsrK-AsrR two-component system. Our results reveal a previously unrecognized AI-2 sensing mechanism and expand our understanding of the physiological roles of AI-2 in bacteria.

Quorum sensing (QS) is considered to be a promising regulation method for biological wastewater treatment (WWT) due to its regulation in extracellular substances (EPS) production, biofilm formation, granulation, colonization and bacterial activity and stability. Recently, autoinducer-2 (AI-2), a kind of interspecies communication QS signal molecule, is being increasingly reported for its roles in regulating bacterial gene expression and aggregation. Consequently, AI-2 mediated QS system is considered as a promising regulatory approach in WWT processes. This article systematically reviews the effects of AI-2-mediated QS system on bacterial behavior and its high potential for real-world applications in different WWT systems. Given the extensive presence of AI-2, AI-2 mediated QS could cooperate with other signal molecules in WWT processes, which suggests that the interactions among multiple signal molecules might be underestimated in the previous studies. The differences between AI-2 and AHL signaling molecules are also compared. Furthermore, the attempts at AI-2 regulated QS in pollution control of different WWT systems are summarized, while some challenges and defects still require targeted research in the future.

Molecularly imprinted polymers (MIPs) have emerged as promising materials for selectively targeting biomolecules, including quorum sensing autoinducers that regulate bacterial communication and biofilm formation. In this study, both single-template and dual-template strategies were employed to design and synthesize MIPs capable of capturing autoinducer-2 analogs using (3R,4S)-tetrahydro-3,4-furandiol (T1) or (R/S) 2,2-dimethyl-1,3-dioxolane-4-methanol (T2) as the templates. This approach offers translational potential of a complementary or non-antibiotic strategy to conventional antimicrobial therapies in mitigating biofilm-associated infections. Computational modeling guided the rational selection of functional monomers, predicting favorable interaction energies (ΔEC up to −135 kcal·mol−1) and optimal hydrogen-bonding patterns to enhance template–polymer affinity. The synthesized MIPs were characterized using spectroscopic and microscopic techniques to confirm imprinting efficiency and structural integrity. The adsorption capacity measurements demonstrated higher adsorption capacity and selectivity of MIPs compared to non-imprinted polymers, with the highest selectivity equal to 3.36 for T1 and 3.14 for T2 on MIPs fabricated from methacrylic acid. Preliminary microbiological evaluations using Chromobacterium violaceum ATCC 12472 reveal that the MIPs prepared from 2-hydroxyethyl methacrylate effectively inhibited violacein production by up to 78.2% at 5.0 mg·mL−1, consistent with quorum sensing interference. These findings highlight the feasibility of employing molecular imprinting to target autoinducer-2 analogs, introducing a novel synthetic strategy for disrupting bacterial communication. This further suggests that molecular imprinting can be leveraged to develop potent quorum-sensing inhibitors, an approach that offers translational potential as an alternative to conventional antimicrobial strategies to mitigate biofilm-associated infections.

Bacteria can coordinate and synchronize activities through a cell density-dependent regulatory mechanism called quorum sensing (QS). Bacteria can measure their population by the synthesis, secretion, and perception of QS signal molecules to regulate specific gene expression when the population reaches a critical threshold. QS participates in various microbial processes such as marine organism bioluminescence, bacterial biofilm formation, and virulence factor expression. The use of QS systems mediated by N-acyl-homoserine lactones and autoinducer-2 has been recently recognized as a promising regulatory approach in environmental science and technology that can intrinsically promote the profound comprehension of wastewater treatment from a microbiology perspective. This article reviewed the study of QS in several environmental systems in wastewater treatment, including systems of aerobic granular sludge, biological nitrogen removal, and bioaugmentation, while several future prospects and suggestions are proposed on the basis of current studies.

Three sequencing batch reactors (M1, M2, and M3) were set up to investigate the influence of different lengths of starvation time (3, 5, and 7 h) on aerobic granulation in the perspective of quorum sensing (QS). Autoinducer-2 (AI-2) level was quantified to evaluate the QS ability of aerobic granules. The results indicated that AI-2 level increased steadily during a cycle of sequencing batch reactors, suggesting that starvation was closely related to AI-2 secretion. In the long-term operation, aerobic granules cultivated using a prolonged starvation period had a better integrity and a higher level of cell adhesiveness despite a slower formation speed. With the extension of the starvation period, the total amount of extracellular polymeric substances (EPS) displayed an increasing tendency. EPS with large molecular weight (MW) also reached a higher level using a prolonged starvation period. However, a higher level of AI-2 and cell adhesiveness was observed in M2, which might be related to more stable granules. The results implied that the starvation period could trigger AI-2 secretion and promoted the production of large MW EPS, leading to cell adhesiveness enhancement and granule formation. Therefore, a combination of different starvation periods was proposed in this study in order to improve aerobic granulation.

Microcystin-LRs (MC-LR) produced by harmful cyanobacterial blooms (HCBs) pose significant hepatotoxic risks to both the environment and public health. Despite the identification and characterization of a limited number of MC-LR degrading bacteria, the challenge of safely removing MC-LRs from freshwater systems without disrupting aquatic ecosystems remains substantial. This study focused on the isolation of lactic acid bacteria from Bapshikhe, a traditional Korean fermented food, and investigated the mechanisms underlying the degradation of MC-LRs by these bacteria. This study also tested the hypothesis that cell wall-associated proteinases in probiotic bacteria play crucial roles in the degradation process. In addition, we verified the hypothesis that the MC-LR degradation mechanism of lactic is correlated with AI-2, a QS-inducing factor. MC-LR degrading bacteria, BSH-02, were successfully isolated from Bapshike, a Korean traditional fermented food, and identified by phylogenetic analysis as Leuconostoc mesenteroides . The BSH-02 strain effectively suppressed cyanobacterial blooms and degraded MC-LR. Ethylenediaminetetraacetic Acid (EDTA), a primary proteinase inhibitor of the BSH-02 strain, reduced the rate of microcystin removal. Based on these studies, the MC-degrading mechanism of BSH-02 was found to involve a metallopeptidase, aligning with mechanisms previously described in other studies. In addition, a correlation between metallopeptidases and AI-2 was identified using RT-qPCR. To the best of our knowledge, this is the first report of Leuconostoc mesenteroides degrading MC-LR. These findings suggest that Leuconostoc mesenteroides strain BSH-02 has high potential for the bioremediation of MC LR-contaminated water bodies.