Coronavirus infections pose a serious threat to human health and have resulted in substantial economic losses to the livestock industry. Coronaviruses invade host cells primarily through two pathways: cell surface membrane fusion and endosomal membrane fusion. During viral entry, the spike protein subunit 1 (S1) recognizes and binds to cellular receptors, while the spike protein subunit 2 (S2) facilitates membrane fusion between the viral envelope and host cell membrane. Due to its high sequence conservation across different coronaviruses, S2 represents an attractive target for the development of broad-spectrum antiviral agents. Blocking S2-mediated membrane fusion can effectively inhibit viral infection. This review summarizes recent advances in understanding the mechanisms of coronavirus entry into host cells, the structure and function of the spike protein, and the development of membrane fusion inhibitors. In addition, this paper discusses the challenges and future prospects in targeting S2 for antiviral drug development, aiming to provide insights for coronavirus prevention and the discovery of novel antiviral therapeutics.

Streptococcus suis is a major zoonotic pathogen that can infect both pigs and humans, causing severe diseases such as meningitis in humans. Its pathogenicity depends on the ability to rapidly adapt to environmental stress and host immune responses. Serine/threonine kinases and their corresponding phosphatases constitute a eukaryotic-like signal transduction system in bacteria and play a key regulatory role in S. suis serotype 2, closely related to its biological characteristics and pathogenic mechanisms. Through precise regulation of the phosphorylation and dephosphorylation of downstream substrates, serine/threonine kinases/phosphatases form complex signaling networks, thereby influencing various physiological and pathogenic processes of the bacterium. This article systematically reviews the currently known substrates of serine/threonine kinases in S. suis serotype 2, with a focus on elucidating how these kinases precisely regulate bacterial growth and division, capsule synthesis, stress tolerance, adhesion, invasion, and pathogenicity by modulating the phosphorylation status of functional substrates. This review aims to provide new perspectives for deciphering the pathogenic mechanism of S. suis serotype 2 and the development of novel antibacterial strategies.

Bovine mastitis is a key factor restricting the high-quality development of China’s dairy industry, while the prevalence of antimicrobial-resistant bacteria and recurrent infections have become severe challenges for the current prevention and control system. Although long-term antibiotic selection pressure may temporarily alleviate clinical symptoms, it significantly accelerates the evolution and dissemination of multidrug-resistant (MDR) pathogens, leading to rising treatment failure rates and a transition toward chronic disease. Epidemiological data indicate that the pathogen spectrum of bovine mastitis in China is dominated by Staphylococcus aureus, Streptococcus spp., and Enterobacteriaceae, with resistance genes propagating across species and regions through horizontal gene transfer (HGT) mediated by plasmids, transposons, and integrons. Furthermore, mechanisms such as biofilm formation, efflux pump activation, target modification, and intracellular escape interact with the mammary microenvironment to establish a robust defense barrier against host immune clearance and antimicrobial agents. Incorporating the principles of endogenous inflammation and metabolic dysregulation mediated by the “gut-mammary axis”, this paper systematically reviews the regional prevalence and molecular dissemination mechanisms of resistant pathogens in China. It provides an in-depth analysis of the pathological basis of recurrence and prospectively proposes comprehensive management strategies—ranging from precision diagnosis to alternative therapies—aiming to provide a theoretical foundation for the scientific control of bovine mastitis.

Dimorphic prosthecate bacteria (DPB) are a group of prokaryotes that reproduce through asymmetric division, producing two morphologically and functionally highly differentiated daughter cells. This unique lifestyle strategy endows them with a competitive advantage in nutrient-poor environments and makes them ideal models for studying bacterial developmental regulation, morphological evolution, and ecological adaptation. This review systematically summarizes the research progress in DPB in terms of their taxonomy, molecular mechanisms of lifestyle regulation, extensive ecological distribution, and environmental adaptation strategies. Additionally, it discusses the application potential of DPB in environmental remediation and biotechnology. Finally, this review makes an outlook on future research directions, aiming to provide a reference for deeply understanding the biological characteristics of these bacteria and expanding their application value.

Objective To clone and express a gene encoding the β-xylosidase from Enterobacter cloacae GX-3, a putative member of the glycoside hydrolase family 3, systematically characterize the recombinant enzyme, and improve the xylose tolerance by molecular engineering of key amino acid residues involved in xylose binding. Methods On the basis of the whole-genome sequencing data of E. cloacae GX-3, primers were designed to amplify the β-xylosidase gene annotated as GH3. The target gene was amplified by PCR and cloned into the pQE30 expression vector, and the resulting recombinant plasmid was transformed into Escherichia coli M15 for induced expression. The recombinant enzyme was purified by nickel-affinity chromatography, and its enzymatic properties were studied. Site-directed mutagenesis was conducted on amino acid residues associated with xylose tolerance. Results The β-xylosidase gene belonging to the GH3 family was successfully cloned from E. cloacae GX-3 and heterologously expressed in E. coli M15. Substrate specificity analysis revealed that the recombinant enzyme EXYL was a multifunctional enzyme exhibiting β-xylosidase, β-glucosidase, and α-L-arabinofuranosidase activities. EXYL showed the optimal performance with the substrate of pNPX and at pH 5.5 and 45 ℃. The K_m and V_max values of this enzyme were (0.73±0.06) mmol/L and (130.00±6.85) μmol/(mg·min), respectively. The inhibition constant (K_i) for xylose was (51.95±2.36) mmol/L. When EXYL acted on xylooligosaccharides (X3-X5), the main products were xylose and xylobiose, each accounting for approximately 50% of the yield. Site-directed mutagenesis of xylose tolerance-related residues yielded positive mutants W138C and W138A, which showed 2.38-fold and 1.83-fold improvements in xylose tolerance, respectively. Conclusion This study provides insights into the multifunctional activities of β-xylosidases and offers new strategies for enhancing the xylose tolerance of β-xylosidases in the GH3 family.

Rice is one of the most widely cultivated and highest-yielding crops worldwide, and its yield stability is closely linked to global food security. As a typical mycorrhizal crop, rice exhibits enhanced growth and stress tolerance after colonization of arbuscular mycorrhizal fungi (AMF). Rhizosphere bacteria, a major component of the rhizosphere microbiome, interact synergistically with AMF, collectively contributing to enhanced nutrient acquisition and improved rice performance. This review summarizes recent advances in the interactions between AMF and rhizosphere bacteria. We highlight that their synergistic interactions regulate rice growth, nutrient acquisition, and stress tolerance, which contribute to the ecosystem stability and biodiversity of the rhizosphere. However, most available studies on the interactions between AMF and rhizosphere bacteria have been conducted under controlled conditions, which limits their applicability to the complex natural field environments. Therefore, this review proposes several suggestions for future research. First, utilize multi-omics technologies such as metagenomics and isotope tracing techniques to elucidate the molecular mechanisms underlying the AMF-bacterial interaction. Second, in practical applications, long-term field positioning trials should be conducted to screen out superior microbial agents that meet the requirements. Finally, optimize regulatory conditions to achieve large-scale propagation of AMF and overcome the bottleneck in AMF field propagation provides theoretical support for promoting the practical application of this technology in agricultural production.

Objective To investigate the antagonistic activity of Bacillus amyloliquefaciens X60 against tobacco phyllosphere microorganisms and its effects on the phyllosphere microbial community of tobacco. Methods Bioactivity assays were conducted to evaluate the antagonistic effects of B. amyloliquefaciens X60 against 20 species of pathogenic fungi, 15 species of non-pathogenic fungi, 2 specialized forms of pathogenic bacteria, and 15 species of non-pathogenic bacteria. Amplicon sequencing was employed to assess the influence of this strain on the phyllosphere microbial community structure. Results B. amyloliquefaciens X60 exhibited strong antagonistic activity (inhibition rates of 60.00%-80.00%) against 13 species of pathogenic fungi (e.g., Rhizopus oryzae) and 12 species of non-pathogenic fungi (e.g., Trichoderma harzianum). Moderate antagonism (inhibition rates of 10.00%-59.00%) was observed against 7 species of pathogenic fungi (e.g., Alternaria tenuissima) and 3 species of non-pathogenic fungi (e.g., Thielavia microspora). Significant antibacterial activity (inhibition zone diameter >20 mm) was detected against 2 specialized forms of pathogenic bacteria (Pseudomonas syringae pv. tabaci and pv. angulata) and 7 non-pathogenic bacteria (e.g., Exiguobacterium). After application, X60 showed the control efficacy of 52.35% against tobacco leaf spot. Following treatment, the relative abundance of Pantoea—a genus of opportunistic bacteria dominating the infected tissue—increased, whereas bacterial diversity and richness initially declined and then recovered. Fungal richness decreased throughout the observation period, while fungal diversity exhibited a transient decrease followed by a rebound. The relative abundance of phytopathogenic fungi declined from 44.87% to 6.71%. Conclusion B. amyloliquefaciens X60 possesses a broad antimicrobial spectrum and exerts strong antagonistic activity against 25 fungal and 9 bacterial species colonizing the tobacco phyllosphere. Under field conditions, the strain provided 52.35% control of tobacco leaf spot and significantly reduced the abundance of foliar phytopathogens, demonstrating the potential as a biocontrol agent for the management of this disease.

Objective To address the problems of rhizospheric microenvironment deterioration and medicinal quality decline caused by continuous cropping obstacles of Fritillaria unibracteata Hsiao et K. C. Hsia, this study explored the regulatory effects of different concentrations of salicylic acid (SA) under continuous and non-continuous cropping patterns and clarified the optimal SA concentration and underlying mechanism for alleviating continuous cropping obstacles, aiming to provide a theoretical basis for optimizing cultivation techniques. Methods A pot experiment was conducted with two cultivation patterns (continuous cropping and non-continuous cropping) and six SA concentration gradients (0, 20, 50, 100, 200, and 500 μmol/L). The changes in root exudates, soil physicochemical properties, soil enzyme activities, alkaloid content, and microbial community structure were determined. Correlation analysis and redundancy analysis (RDA) were performed to elucidate the regulation mechanism. Results SA exerted significant concentration-specific regulatory effects on the rhizospheric microenvironment and alkaloid biosynthesis of F. unibracteata, showcasing a significant interaction effect with cultivation patterns. Total phenolic acids in root exudates increased under 20 μmol/L and 500 μmol/L SA treatments (P<0.05), and organic acids reached the peak under 200 μmol/L SA treatment. The soil organic carbon and soil organic matter in the non-continuous cropping group were significantly higher than those in the continuous cropping group. SA at 50 μmol/L optimized soil pH, increased the supply of available phosphorus and ammonium nitrogen, and enhanced the activities of urease and acid phosphatase. Pseudomonadota and Ascomycota were the dominant phyla in bacterial and fungal communities, respectively. SA at 500 μmol/L enriched beneficial microorganisms such as Streptomyces, inhibited pathogens, and specifically increased the content of peimisine and sipeimine. RDA results showed that SA remodeled the microbial community by regulating the composition of root exudates, thereby mediating alkaloid biosynthesis. Conclusion SA at 50 μmol/L SA is suitable for optimizing rhizosphere nutrient supply and enzyme activities, and that at 500 μmol/L is suitable for effectively alleviating continuous cropping obstacles and promoting the accumulation of medicinal alkaloids. SA achieves rhizospheric ecological restoration and medicinal quality improvement through a synergistic pathway of regulating root exudate composition, remodeling microbial community structure, and repairing rhizospheric interaction network. This study provides a new approach for the management of continuous cropping obstacles for F. unibracteata.

Excessive nitrogen input caused by eutrophication in nearshore waters is a major environmental stressor driving the global degradation of seagrass beds. Objective To screen and identify efficient aerobic denitrifying bacteria from seagrass bed ecosystems and elucidate their nitrogen removal performance and mechanisms, thus providing microbial resources for alleviating nitrogen loading and restoring eutrophic seagrass beds. Methods Aerobic denitrifying bacteria were isolated and screened from seagrass rhizosphere sediments in Zhifu Bay, Yantai by enrichment-domestication culture and bromothymol blue assay. The taxonomic status of the strains was determined by 16S rRNA gene sequencing. On the basis of nitrogen removal performance, an efficient aerobic denitrifying strain was selected. Single-factor and orthogonal experiments were conducted to optimize its denitrification conditions, and nitrogen balance experiments and whole-genome sequencing were employed to elucidate its nitrogen removal pathways and key functional genes. Results A total of 34 denitrifying strains were isolated from seagrass rhizosphere sediments in Zhifu Bay, Yantai. The dominant genera were Pseudomonas and Acinetobacter. A strain designated as Pseudomonas sp. S22 with high denitrification performance was selected. The denitrification conditions of this strain were optimized as follows: sodium succinate as the carbon source, C/N=15, pH 9.0, salinity (S)=30‰, and T=28 ℃. Under these conditions, the strain achieved a removal rate of 99.99% for 140 mg/L nitrate nitrogen within 36 h, demonstrating excellent nitrogen removal efficiency. Nitrogen balance analysis revealed that approximately 59.64% of the initial nitrate nitrogen was converted to gaseous nitrogen, confirming that denitrification was the dominant nitrogen removal pathway. Genomic sequencing revealed that strain S22 carried key functional genes for aerobic denitrification, including napA and nirS, providing a genetic basis for its denitrification phenotype at the molecular level. Conclusion This study systematically isolated and identified aerobic denitrifying bacteria from seagrass beds in northern China. Strain S22 exhibits outstanding nitrogen removal performance and environmental adaptability. Nitrogen balance and genomic analyses confirm that denitrification is its primary nitrogen removal pathway and the strain carries key functional genes for aerobic denitrification. Strain S22 can serve as a potential microbial resource for reducing nitrogen loading in seagrass beds. This study provides both a valuable strain and a theoretical basis for the future development of microbe-seagrass synergistic remediation technologies.

Sugarcane smut is a severe fungal disease caused by Sporisorium scitamineum, resulting in yield reduction and economic losses. Reversible protein phosphorylation plays a crucial role in the sexual mating and pathogenicity of S. scitamineum. Protein phosphatases, as key regulators of reversible protein phosphorylation, remain poorly characterized in S. scitamineum. Objective To elucidate the biological functions of the protein phosphatase SsPpe1 in S. scitamineum, providing a potential target for effective control of sugarcane smut. Methods We constructed overexpression mutants OE-Ssppe1 by Agrobacterium-mediated genetic transformation technology and analyzed the sporidium morphology, sexual mating ability, stress tolerance, and pathogenicity. Results The OE-Ssppe1 sporidia exhibited pseudohyphal morphology with multiple nuclei and abnormal chitin accumulation. The OE-Ssppe1 mutants showed reduced tolerance to NaCl and SDS, sexual mating, and pathogenicity. RT-qPCR and RNA-seq analyses revealed that Ssppe1 overexpression affected the expression of genes related to pheromone response, MAPK, and cAMP-PKA signaling pathways. In addition, Ssppe1 overexpression affected protein synthesis and folding process. Conclusion The protein phosphatase SsPpe1 is involved in regulating the sporidium morphology, stress responses, sexual mating, and pathogenicity of S. scitamineum. These findings provide a theoretical basis for thoroughly elucidating the pathogenic mechanisms of S. scitamineum and developing targeted disease control strategies.