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.

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.

Ciliates of the family Balantidiidae widely parasitize the digestive systems of various invertebrates and vertebrates. Among them, Balantioides coli with cosmopolitan distribution is a major zoonotic pathogen. For a long time, due to the similar morphology of trophozoites of Balantidiidae ciliates from various hosts and the influences of various growing stages and host intestinal microenvironments on morphological characteristics, there have been some inconsistencies and confusions in their classification and nomenclature in literature. Recently, significant progress has been achieved in the study of the phylogenetic relationship and genetic diversity of Balantidiidae ciliates, providing new evidences for their taxonomic reconstruction. On the basis of a systematic review of literature and our findings, this article summarizes the taxonomic status and genetic diversity of Balantidiidae ciliates from different hosts in terms of the morphological characteristics, encystation ability, host specificity, and phylogenetic relationships. The existing evidence supports the division of the family Balantidiidae into two genera Balantidium and Balantioides and indicates that the ciliate infecting humans and various mammals should be classified as Balantioides coli. The related findings and understanding help clarify the taxonomy and nomenclature system of Balantidiidae ciliates and provide an important reference for studying the biological characteristics of Balantidiidae ciliates as well as the diagnosis and control of balantiosis in humans and animals.

Alzheimer’s disease (AD) is a complex neurodegenerative disorder characterized by progressive cognitive impairment. In recent years, the “gut-brain axis” has been recognized to play an important role in the pathogenesis of AD, with the gut microbiota-derived metabolites serving as key mediators of gut-brain communication. This review systematically summarizes the alterations and underlying molecular mechanisms of five classes of key metabolites—short-chain fatty acids, bile acids, indole derivatives, trimethylamine N-oxide, and lipopolysaccharides—during the progression of AD. This review not only provides new perspectives for understanding the pathological processes of AD but also lays a theoretical foundation for the development of diagnostic and therapeutic strategies based on microbiota modulation.

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 achieve high-level expression and purification of the recombinant 9 kDa and 15 kDa chicken NK-lysin proteins (designated as cNKL9 and cNKL15) and evaluate their in vitro antibacterial and immunomodulatory activities. Methods The target genes—cNKL9 and cNKL15—were individually cloned into the pPIC9K vector to construct recombinant expression plasmids for heterologous expression in Pichia pastoris. After confirming the correct expression of the recombinant proteins via SDS-PAGE and Western blotting, we used nickel affinity chromatography to obtain highly purified recombinant cNKL9 and cNKL15 proteins. The in vitro antibacterial activitiesof recombinant proteins against Salmonella typhimurium and Escherichia coli O157:H7 were assessed by colony forming unit (CFU) assays. We measured the mRNA levels by RT-qPCR and analyzed the transcriptional changes of relevant cytokines after applying the recombinant proteins to the chicken macrophage cell line HD11. High-level expression of the recombinant proteins was achieved in a 15 L fermenter for scale-up culture via optimization of the high-density fermentation process. Results The P. pastoris expression plasmids pPIC9K-cNKL9 andpPIC9K-cNKL15 were successfully constructed. SDS-PAGE and Western blotting results revealed specific bands of recombinant cNKL9 and cNKL15 proteins in the culture supernatant, confirming the successful secretory expression of the target proteins. Antibacterial activity assay demonstrated that the recombinant cNKL9 protein exhibited significant inhibitory activities against both S. typhimurium and E. coli O157:H7, whereas the recombinant cNKL15 protein showed no obvious inhibitory effects on either pathogenic strain. RT-qPCR analysis showed that the recombinant cNKL15 protein significantly upregulated the transcription levels of cytokines such as CCL4 and CCL20 in HD11 cells, while the recombinant cNKL9 protein did not exhibit immunomodulatory activity. Furthermore, in the 15 L fermenter, the heterologous expression yields of cNKL9 and cNKL15 reached 0.64 g/L and 0.53 g/L, respectively. Conclusion For the first time, we achieved high-level expression of recombinant cNKL9 and cNKL15 proteins in the P. pastoris system. Specifically, cNKL9 exhibited inhibitory activities against S. typhimurium and E. coli O157:H7, while cNKL15 exerted immunomodulatory effects by upregulating the mRNA levels of cytokines in the chicken macrophage cell line HD11. These findings provide experimental evidence for the development of cNKL9 and cNKL15 as antibacterial or immunomodulatory agents, indicating their considerable application potential.

Neurodegenerative diseases, a group of highly prevalent central nervous system disorders, are closely linked to gut microbiota dysbiosis and impaired gut-brain axis function. The emerging gut-brain axis theory offers a novel perspective to explain how microbes exert remote, cross-organ regulation over the central nervous system. Recent studies have indicated that butyrate-producing bacteria, a core functional component of the gut microbiota, exhibit dynamic changes temporally and spatially correlated with the onset and progression of these diseases. These bacteria are thought to modulate the central nervous system microenvironment and disease pathology via the gut-brain axis. This article systematically reviews the bidirectional signaling mechanisms between the gut microbiota and the brain, analyzing the complex, multidimensional relationship between butyrate-producing bacteria and neurodegenerative diseases. This analysis encompasses population heterogeneity in patients with diverse clinical features and the dynamic evolution of these bacterial communities across different disease stages. We summarize the key mechanisms by which butyrate-producing bacteria regulate disease progression, including barrier protection, immunomodulation, metabolic regulation, and epigenetic modification. Furthermore, we explore their clinical potential as predictive biomarkers and therapeutic targets. We propose that future research should prioritize the development of targeted intervention strategies for gut-derived butyrate-producing bacteria. This review aims to provide a theoretical foundation and novel insights to advance both the fundamental investigation and clinical translation of these bacteria in the context of neurodegenerative diseases.

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.

Salicylic acid (SA) is an important phenolic compound that plays a key role in plant defenses and is widely used in pharmaceuticals, cosmetics, and personal care products due to its significant anti-inflammatory and antimicrobial activities. Currently, the production of SA mainly relies on plant extraction and chemical synthesis, which suffers from complex processes, severe environmental pollution, and high dependence on petrochemical resources. With the rapid development of synthetic biology, metabolic engineering, and artificial intelligence (AI) technologies, the green synthesis of SA through intelligently designed microbial cell factories, empowered by machine learning algorithms and automated platforms, has become an important research direction to replace conventional production methods. This review systematically summarizes the microbial biosynthetic pathways of SA. With a focus on the intelligent design theme, this paper highlights the application of AI and synthetic biology tools in the discovery and utilization of natural SA-producing microbial resources and the rational reconstruction and optimization of the SA biosynthetic pathway in model microorganisms via intelligent metabolic engineering strategies. Furthermore, it introduces the key intelligent technologies for enhancing yields and the challenges faced. Finally, it discusses the future trends in this field.

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.