Mobile genetic elements drive bacterial evolution, while exposing bacteria to the risk of invasion by “selfish genes”. In the arms race with mobile genetic elements, bacteria have evolved a range of immune systems that can protect hosts from invading nucleic acids. These immune systems are capable of preventing the invasion of mobile genetic elements, degrading invading nucleic acids, inhibiting the replication or transcription of invading nucleic acids, or inducing abortive infections to protect the population. Although much is known about the working mechanisms of these host immune systems, it remains unclear how bacteria orchestrate different defense strategies in response to different stages of nucleic acid invasion. Based on our research and different immune strategies of bacteria to limit mobile genetic elements in different spatiotemporal dimensions, this review summarizes and classifies the host immune systems. The elucidation of these multilayered immune mechanisms not only reveals the arms race between host and mobile gene elements in the evolutionary process but also underpins the development of new biotechnologies.

Streptococcus pneumoniae is a common opportunistic pathogen that can cause various infectious diseases, including acute otitis media, bronchitis, sinusitis, community-acquired pneumonia, septicemia, and purulent meningitis. Autophagy, a lysosome-dependent intracellular degradation pathway, plays a dual regulatory role in both bacterial infection and host defense against pathogens. During S. pneumoniae infection, host cells can activate xenophagy to eliminate invading bacteria. However, this pathogen has evolved multiple evasion strategies, such as interfering with autophagosome maturation, escaping autophagic encapsulation, and even hijacking the autophagy pathway to promote intracellular survival and dissemination. Recent years have witnessed significant progress in understanding the molecular mechanisms underlying the dynamic interplay between S. pneumoniae and host autophagy systems during bacterial infection, yet a systematic review synthesizing these findings remains unavailable. This review focuses on the interaction network and key mechanisms of S. pneumoniae with host cell autophagy, aiming to provide theoretical foundations and research perspectives for developing novel targeted therapeutic strategies against S. pneumoniae infections.

Bacterial glycoproteins, glycolipids, and polysaccharides are collectively known as glycans, which can serve as pivotal pathogenic factors leading to infection. Bacterial protein glycosylation mainly includes N-glycosylation, O-glycosylation, S-glycosylation, and arginine glycosylation. Glycolipids and polysaccharides are also important glycoconjugates, mainly including lipopolysaccharides, lipoarabinomannan, rhamnolipids, peptidoglycan, teichoic acids, and capsular polysaccharides. Bacterial glycoconjugates can promote host-pathogen interactions, influencing bacterial virulence, drug resistance, and biofilm formation, thereby facilitating bacterial infection. In addition, bacterial glycoconjugates can exert dual effects by modulating the host immune system: on one hand, aiding bacteria in achieving immune evasion and causing host infection; on the other, activating host immunity to help eliminate bacteria and suppress infection. This article provides an overview of bacterial glycans regarding the types, structural characteristics, roles in bacterial adhesion and colonization, and regulation of host immune responses and summarizes the effects of bacterial glycans on infection, aiming to offer a distinct perspective from glycoimmunology and an alternative strategy for clinical prevention and treatment of bacterial infectious diseases.

The potent antibacterial activity of silver nanoparticles is primarily attributed to the release of silver ions, which disrupt cell membranes and inactivate essential enzymes through Ag-S bonding formation. Objective To explore silver ion immobilization to minimize silver release. Methods A macrocyclic cryptand with nitrogen bridgeheads was prepared and subsequently chelated with silver ions to produce Cage silver(I), which was then coordinated with different ratios of sulfonated chitosan (SCS) to form SCS/Cage Ag(I) complexes (SCA1, SCA2, and SCA3). The antioxidant activities of the complexes were assessed by reducing power and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical and hydrogen peroxide scavenging assays. The antibacterial activities of the complexes were evaluated based on the minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) against Staphylococcus aureus ATCC 6538 and Escherichia coli O157:H7 and the inhibition rate on biofilm formation. Results Cage silver(I) exhibited strong antibacterial activity, with the MIC of 0.015 mg/mL and MBC of 0.031 mg/mL against S. aureus ATCC 6538, and the MIC of 0.031 mg/mL and MBC of 0.120 mg/mL against E. coli O157:H7. Significant antioxidant properties of Cage silver(I) were also observed, as demonstrated by the DPPH free radical scavenging rates of 42.2% and 53.1% at 326 nm and 517 nm, respectively. Cage silver(I) exhibited the highest antibacterial and antioxidant activities, followed by SCA1, SCA2, SCA3, and SCS, because the content of silver ions in Cage silver(I) was 10-fold higher than that in SCA1. The antibacterial and antioxidant activities of SCA1 were better than those of Cage silver(I), which further indicated that the sulfonic groups of SCS may intensely coordinate with silver ions to exert synergistic effects. Conclusion Combining the merits of silver ions and SCS improves the bioavailability of the agent at microbicidal concentrations, minimizes the accumulation in the environment, and reduces treatment costs. The method developed herein offers a sustainable approach to enhance microbial control while minimizing the impact on the environment.

Objective The probiotic Escherichia coli Nissle 1917 (ECN) is engineered by synthetic biology to construct a tumor-targeting strain capable of colonizing the tumor tissue, converting glucose and metabolic waste ammonia in the tumor microenvironment into the photosensitizer precursor 5-aminolevulinic acid (5-ALA) and the immunomodulatory amino acid arginine, while synergizing with immune checkpoint inhibitors for enhanced antitumor efficacy. Methods The genes hemA^M, hemL, and argA were co-expressed in ECN, and thyA was knocked out via the λ-Red homologous recombination system to improve the tumor-targeting specificity. Shake-flask fermentation experiments, UV spectrophotometry, and HPLC were employed to quantify 5-ALA and arginine production. The antitumor effects of the engineered ECN were systematically evaluated by in vitro cellular assays and a murine colorectal cancer model. Results The engineered strain achieved 5-ALA and arginine yields of (173.00±11.46) mg/L and (1.70±0.09) g/L, which represented 8.2-fold and 20-fold increases, respectively, over that of wild-type ECN (P<0.000 1). The deletion of thyA enabled selective proliferation of the strain in tumor cells (HCT116 and CT26), with a two-fold increase in OD₆₀₀ compared with that in normal Vero cells (P<0.000 1), confirming enhanced tumor targeting. Both in vitro and in vivo experiments demonstrated sustained synthesis of 5-ALA and arginine in tumors. Compared with wild-type ECN, the engineered strain induced 2.7-fold and 1.9-fold increases in CD8⁺ and CD4⁺ T-cell infiltration (P<0.000 1), alongside 1.7-fold and 2.4-fold elevations in IL-6 and TNF-α secretion (P<0.000 1), respectively. The engineered strain combined with the anti-PD-L1 therapy achieved a tumor volume inhibition rate of 77.6% (P<0.000 1). Conclusion This study establishes a metabolically and immunologically dual-functional ECN platform that synergizes localized delivery of photodynamic therapy precursors, arginine-mediated immunometabolic reprogramming, and immune checkpoint blockade, providing a novel solution for the combined therapy against solid tumors. The engineered system offers a groundbreaking strategy for precise tumor microenvironment modulation, advancing the research on targeted cancer therapeutics.

Objective To analyze the activity of ribose-5-phosphate isomerase B (RpiB) encoded by lmo0736 and explore its effect on the infection of Listeria monocytogenes (LM). Methods The recombinant protein Lmo0736 was obtained by prokaryotic expression and purification, and its catalytic activity for substrates was verified by the enzyme activity assay. The LM strain with lmo0736 knockout (LM Δlmo0736) and the complementary strain (LM CΔlmo0736) were constructed by bacterial homologous recombination. The growth curves of bacteria in vitro were plotted. The adhesion, invasion, and intercellular migration of bacteria were evaluated by in vitro cell infection models (Caco-2 intestinal epithelial cells and L929 fibroblasts). The ICR mouse infection model was used to measure the 7 d survival rate and 48 h organ load of each strain, and thus the pathogenicity of strains in mice was evaluated. Results Lmo0736 had typical RpiB activity and catalyzed the conversion of d-ribose-5-phosphate to d-ribulose-5-phosphate, with V_max=0.366 mmol/(L·min), K_m=4.489 mmol/L, k_cat=12.300 s^-1, and k_cat/K_m=2.740 L/(mmol·s). The growth rate of LM Δlmo0736 was not significantly different from that of the wild type EGD-e and LM CΔlmo0736in vitro, indicating that the deletion of lmo0736 did not affect the basic growth of bacteria. LM Δlmo0736 demonstrated significantly decreased adhesion and invasion in Caco-2 cells and intercellular migration in L929 cells and weakened colonization in mice, which indicated that lmo0736 regulated the pathogenicity of LM through a RpiB-dependent metabolic pathway. Conclusion This study reveals for the first time that the Lmo0736 of LM has typical RpiB activity. Although the functional loss of Lmo0736 does not directly affect the basic growth of the bacteria, it significantly attenuates the pathogenicity by weakening the adhesion, invasion, and intracellular migration in host cells and the colonization in vivo. The results accumulate experimental data for in-depth exploration of the biological functions of RpiB in LM. From the perspective of the association between metabolism and virulence, this study provides an experimental basis for delving into the infection mechanism of foodborne pathogens.

Objective To screen the biocontrol bacterial isolates with antagonistic activity against root rot pathogens of Panax notoginseng from the rhizosphere of Bletilla striata in a P. notoginseng-B. striata rotation system, identify the isolates, and evaluate their control effects, thereby providing a scientific basis for the application of P. notoginseng-B. striata rotation in alleviating continuous cropping obstacles and screening biocontrol strains from the rhizosphere of the plants for rotation rather than from that of target plants in the plant rotation system for controlling soil-borne diseases in the field. Methods The dilution plate method was employed to isolate culturable microorganisms from the rhizosphere soil of B. striata. The antagonistic activities of the isolates against root rot pathogens of P. notoginseng were evaluated via the dual culture assay. Molecular identification was performed based on the 16S rRNA gene sequence. In pot experiments, antagonistic bacteria were inoculated, and then the ability of antagonistic bacteria to control root rot was evaluated based on the root rot incidence of P. notoginseng. Results The rotation with B. striata significantly reduced the incidence and disease index of P. notoginseng root rot compared with continuous cropping. A total of 200 bacterial strains were isolated from the rhizosphere soil of B. striata, from which 25 strains exhibiting antagonistic activities against the root rot pathogens including Ilyonectria destructans RS6, Fusarium solani F3, and Fusarium oxysporum Z5 of P. notoginseng were screened out. The isolation efficiency of antagonistic bacteria was 12.5%. The 25 strains were identified as 12 species belonging to 5 genera, demonstrating rich diversity. There were 14 strains of Bacillus sp., including 4 strains of B. subtilis, 2 strains of B. velezensis, 6 strains of B. amyloliquefaciens, 1 strain of B. cereus, and 1 strain of B. toyonensis. There were 5 strains of Acinetobacter, including 2 strains of A. johnsonii, 2 strains of A. junii, and 1 strain of A. pittii. There were 4 strains of Pseudomonas, including 3 strains of P. putida and 1 strain of P. fulva. In addition, 1 strain of Enterobacter asburiae and 1 strain of Aeromonas caviae with antagonistic activities were isolated. Four strains (B. amyloliquefaciens BJ1, B. subtilis BJ7, B. amyloliquefaciens BJ8, and A. johnsonii YB10) antagonistic to all the three pathogens were applied to continuous cropping soil. They significantly reduced the root rot incidence and enhanced the fresh weight of P. notoginseng. Conclusion The rhizosphere soil of B. striata in rotation with P. notoginseng harbors diverse biocontrol strains against the root rot pathogens of P. notoginseng. This study lays a theoretical foundation for the rotation of P. notoginseng with B. striata to alleviate continuous cropping obstacles.

Objective To investigate the effect of Lactobacillus reuteri CCTCC M 2016546 on chronic unpredictable mild stress (CUMS)-induced depression in rats and explore its potential mechanism. Methods Sixty male Sprague-Dawley (SD) rats were initially randomized into three groups: blank control (n=8), CUMS model (n=43), and prevention (n=9). The other groups except the blank control group received three CUMS stimuli daily. The prevention group was administrated with the L. reuteri CCTCC M 2016546 suspension (1×10⁹ CFU/d) via oral gavage prior to daily stress induction. After 4 weeks, depressive behaviors were assessed by sucrose preference, forced swimming, and open field tests. Successfully modeled rats (n=43) were re-randomized into five groups: model control (n=8), fluoxetine (2.1 mg/kg, n=8), combined therapy (2.1 mg/kg fluoxetine+1×10⁹ CFU/d CCTCC M 2016546, n=9), high-dose CCTCC M 2016546 (5×10⁹ CFU/d L. reuteri CCTCC M 2016546, n=9), and low-dose CCTCC M 2016546 (1×10⁹ CFU/d CCTCC M 2016546, n=9). Rats were administrated with corresponding agents daily for 4 weeks and then subjected to behavioral tests again. The levels of 5-hydroxytryptamine (5-HT) in the hippocampus and adrenocorticotropic hormone (ACTH) and cortisol (CORT) in the serum were quantified via ELISA. Western blotting was performed to determine the protein levels of brain-derived neurotrophic factor (BDNF), tyrosine kinase receptor B (TrkB), protein kinase B (Akt), phosphatidylinisitol 3-kinase (PI3K), extracellular signal-regulated kinase (ERK), and cAMP-response element binding protein (CREB) in the brain tissue. Results Compared with the model control group, all treatment modalities (fluoxetine, combined therapy, and CCTCC M 2016546) alleviated depressive behaviors: increasing sucrose preference (P<0.01, P<0.001), reducing immobility time in suspension (P<0.01, P<0.05), and enhancing horizontal locomotion distance/central zone exploration (P<0.01, P<0.05). Biochemical analyses revealed that treatments reversed the CUMS-induced alterations in 5-HT, CORT, and ACTH levels (P<0.01, P<0.05). Western blotting demonstrated upregulated protein levels of BDNF, PI3K, CREB, TrkB, Akt, and ERK in the fluoxetine and combined therapy groups (P<0.01, P<0.05). High-dose CCTCC M 2016546 elevated Akt, BDNF, CREB, and PI3K levels (P<0.01, P<0.05), while low-dose CCTCC M 2016546 raised Akt and BDNF levels (P<0.01). Prophylactic CCTCC M 2016546 administration primarily enhanced TrkB expression (P<0.05). Conclusion L. reuteri CCTCC M 2016546 ameliorates CUMS-induced depression in rats, potentially by modulating the hypothalamic-pituitary-adrenal axis hyperactivity and activating the PI3K/Akt/CREB/BDNF signaling pathway.

Objective To elucidate and compare the diversity, structure, and functional characteristics of gut microbiota in sympatric fish species from a perspective of microbial ecology and explore the role of gut microbiota in feeding habit and ecological niche differentiation. Methods Foregut, midgut, and hindgut samples from Gymnocypris eckloni and Schizopygopsis pylzovi, along with their aquatic environmental samples, were collected from the upper Yellow River. The gut microbiota and potential functions were compared by 16S rRNA gene high-throughput sequencing and multiple bioinformatics approaches. Results Microbial alpha diversity followed the trend of aquatic environment>S. pylzovi>G. eckloni (P<0.05). In G. eckloni, alpha diversity was highest in the foregut, whereas in S. pylzovi, it decreased progressively from the foregut to the midgut and then to the hindgut. Beta diversity analysis based on clustering and CPCoA demonstrated that microbial communities derived from different gut segments of the same species were more similar to each other than those derived from the same gut segment of different species, indicating that the differences attributable to species were greater than those attributable to gut segments (P<0.001). Pseudomonadota accounted for over 50.00% of the gut microbiota in all sample types, while Bacillota comprised more than 25.00% in the guts of both fish species, which was significantly higher than that (3.80%) observed in the aquatic environment. Fusobacteriota and Cetobacterium were nearly absent in water and S. pylzovi but showed high abundance in the midgut and hindgut of G. eckloni. Enterococcus was specifically enriched in the hindgut of G. eckloni, while Lactococcus were predominantly found in the hindgut of S. pylzovi. PICRUS2 functional prediction revealed that gut microbiota of both species primarily enriched amino acid and carbohydrate metabolism pathways. The enriched metabolic pathways varied significantly across different gut segments of S. pylzovi, while significant differences in signaling molecules and interaction, cardiovascular diseases, and metabolism of terpenoids and polyketides were noted for the same gut segments between the two species. Conclusion There were significant differences in the microbiota composition and diversity in the gut between the two fish species and their aquatic environments, with distinct gut microbiota functions for each species. This study establishes a micrological foundation for research on the feeding habit and ecological niche differentiation of fish and provides theoretical support for exploitation of gut microbial resources and conservation and resource management of plateau fish species.

Myosmine, also known as 3-(3,4-dihydro-2H-pyrrol-5-yl) pyridine, is a tobacco alkaloid found not only in tobacco but also in various foods, fruits, and vegetables. It serves as one of the precursors for the formation of the carcinogenic tobacco-specific nitrosamine N′-nitrosonornicotine, posing a potential threat to human health. Objective To screen bacterial strains capable of degrading myosmine and preliminarily explore the pathways and mechanisms underlying myosmine degradation. Methods We used myosmine as the sole carbon source to enrich and isolate the myosmine-degrading bacterial strain from tobacco-growing soil. Taxonomic identification of this myosmine-degrading strain was achieved by a combination of morphological observation, physiological and biochemical testing, and molecular analysis. The myosmine degradation products by this strain were analyzed by HPLC and UHPLC-MS/MS. The degradation genes were predicted by BLAST comparison. Results A strain G-2 capable of degrading myosmine was successfully isolated. The strain was identified as a member of Shinella, designated Shinella sp. G-2. HPLC and UHPLC-MS/MS identified five degradation products. Genomic analysis showed that strain G-2 possessed a homologous gene cluster of a variant of the pyridine and pyrrolidine pathway (VPP) gene cluster. Conclusion In this study, a strain Shinella sp. G-2 with the ability to degrade myosmine was isolated. Strain G-2 might use enzymes in the VPP pathway to degrade myosmine through a metabolic pathway similar to the VPP pathway.