Frontiers in Microbiology最新文献

Nutrient deficiencies in alkaline soils (pH 7.9-8.5) frequently limit plant growth due to insufficient nutrient availability and uptake. This study investigated the effects of two bacterial strains, VITK-1 (Pseudomonas sp.) and VITK-3 (Burkholderia sp.), on nutrient absorption, growth, and gene expression in tomato (Solanum lycopersicum) seedlings grown in alkaline soil. Bacterial treatments were applied individually and as a consortium, and their ability to promote plant growth and nutrient solubility was evaluated. In vitro studies demonstrated the strains' ability to solubilize essential nutrients, generate extracellular enzymes, and exhibit a variety of Plant Growth-Promoting Rhizobacteria (PGPR) characteristics, with strong antagonistic activity against Fusarium oxysporum f.sp. lycopersici and Ralstonia solanacearum (35.7%-76.5%). In vivo investigations revealed notable improvements in germination (73.3%), root and shoot development, and overall seedling vigor when compared to untreated controls. The bacterial consortium significantly improved protein (54.5%) and proline (69.5%) levels, antioxidant activity (50.7%), phenolic (60.9%), and flavonoid content (52.5%), and decreased carbohydrate accumulation. Furthermore, treated plants exhibited activation of nutrient-regulating genes (NRT2, PR-1, and AMT-1) associated with better root metabolism (improved 1.58-1.70 mg) and resilience to stress (GR-1 and DREB3). These results show the potential of PGPR inoculants, particularly consortia, as a promising strategy for improving nutrient uptake, biochemical characteristics, and stress tolerance in crops grown in alkaline soils.

Probiotics are well recognized for their ability to modulate host immune responses; however, growing evidence indicates that many of their beneficial effects are mediated by structural components rather than by viable microorganisms. Among these components, probiotic-derived peptidoglycan has emerged as a key immunologically active molecule with a critical role in regulating both innate and adaptive immunity. Although substantial experimental data exist regarding its underlying mechanisms, the context-dependent immunomodulatory and anti-inflammatory functions of peptidoglycan have not been comprehensively integrated. In this review, we provide an up-to-date and comprehensive overview of the molecular and cellular mechanisms that govern the immunoregulatory properties of probiotic-derived peptidoglycan. We first discuss the structural diversity and processing of peptidoglycan and their implications for host recognition via pattern-recognition receptors, particularly Toll-like receptor 2 (TLR2) and nucleotide-binding oligomerization domain proteins 1 and 2 (NOD1/2). We then critically evaluate current evidence supporting the therapeutic potential of probiotic-derived peptidoglycan in infectious diseases, inflammatory bowel disease (IBD), autoimmune disorders, allergic inflammation, and cancer. Collectively, these findings suggest that peptidoglycan holds considerable promise for the development of next-generation microbiota-based immunotherapeutic strategies.

Ruminants play an essential role in food production due to their ability to utilize forages through fermentation in the rumen. This fermentative chamber hosts a diverse microbial community capable of degrading fiber and non-fiber carbohydrates, producing short-chain fatty acids (SCFAs) and microbial protein, which are essential for the animal's metabolism. Throughout their evolution, ruminants developed a symbiotic relationship with microorganisms specialized in the degradation of plant fibers, enabling the use of forages as a dietary foundation. However, modern intensive production systems have introduced concentrate ingredients to their diets (such as grains and industrial by-products), which represent a significant departure from ancestral diets based exclusively on forages. Dietary composition is the primary factor driving changes in the ruminal microbiota and can significantly alter its composition. Variations in the forage-to-concentrate ratio can drastically alter microbial activity, affecting the stability of the ruminal ecosystem. Sequencing technologies and omics approaches have enhanced the understanding of this ecology, allowing for more effective nutritional interventions. The objective of this review is to assess how contemporary diets in intensive production systems differ from ancestral, forage-only diets and how these differences reshape the ruminal microbiota. To this end, we characterized the variations in the ruminal microbiota composition of animals fed high-concentrate and high-forage diets, describing the specific microbial profiles of each condition and identifying beneficial and potentially detrimental microorganisms. This review synthesizes current evidence on how dietary transitions reshape ruminal microbial cross-feeding networks and proposes an integrative framework linking microbial symbiotic balance, rumen health, and production efficiency. By emphasizing the dynamic regulation of microbial interactions rather than isolated taxa, this work highlights cross-feeding stability as a central target for nutritional, microbial, and genetic interventions in intensive ruminant production systems.

Canine coronavirus (CCoV) is an important enteric alphacoronavirus primarily affecting canids. Here, we detected canine coronavirus RNA in a captive 9-year-old Amur tiger (Panthera tigris altaica) in China. The complete viral genome was obtained using metagenomic next-generation sequencing. Phylogenetic and recombination analyses were then performed to investigate its evolutionary relationship with canine and feline coronaviruses. The identified CCoV strain clustered within established canine coronavirus lineages and showed sequence evidence of recombination involving coronavirus strains previously reported in other carnivore species. Although the detection of viral RNA alone does not establish a causal relationship between CCoV infection and disease outcome, this study provides molecular evidence that Amur tigers are susceptible to canine coronavirus infection. These findings expand the known host range of CCoV and contribute to understanding the evolution and cross-species transmission potential of coronaviruses among carnivores.

Introduction: Mineral deficiency is a major nutritional issue that threatens human health. Probiotics, owing to their ability to enhance intestinal absorption, are regarded as potential nutritional modulators.

Methods: In this study, multiple strains of Lactobacillus and Bifidobacterium were systematically evaluated for their in vitro fermentation metabolism and mineral absorption-promoting properties to screen probiotic candidates possessing mineral uptake-enhancing potential. Eight strains selected via multi-parameter screening were further evaluated for their mineral absorption-promoting capacity using the Caco-2 cell model.

Results: The results revealed significant strain-specific differences in acid production capacity, short-chain fatty acids (SCFAs) generation, and phytase activity. Strains L. paracasei PC-01, B. lactis Ca360, L. plantarum Fe-01, B. lactis MN16620, and L. brevis MN14440 exhibited pronounced acid-producing ability, indicated by markedly decreased fermentation broth pH values. L. reuteri MN11965, L. acidophilus MN06785, L. brevis MN06618, and L. rhamnosus MN08244 showed significantly higher L-lactic acid yields than the positive control. Acetate was the predominant metabolite, followed by propionic and butyric acids, with L. curvatus MN15933, B. lactis Ca360, and B. lactis MN16620 showing particularly strong butyrate production. Phytase activity assays revealed that both intracellular and extracellular enzyme activities of L. plantarum Fe-01 and B. lactis Ca360 were significantly higher than those of L. plantarum 299v. In the Caco-2 cell model, all tested strains significantly increased calcium uptake, with L. plantarum Fe-01 and B. lactis Ca360 showing the highest transmembrane calcium transport efficiency. These two strains also markedly enhanced iron absorption, while B. lactis Ca360 exhibited zinc uptake and transport levels comparable to the positive control.

Discussion: Comprehensive analysis indicated that strain B. lactis Ca360 demonstrated the most prominent effect in promoting calcium, iron, and zinc absorption, likely through mechanisms involving acid production-induced pH reduction and phytate hydrolysis facilitation. This study provides systematic verification of the integrated mechanisms by which probiotics promote mineral absorption and offers both theoretical support and strain resources for the development of targeted probiotics aimed at improving mineral bioavailability.

Background: Clostridioides difficile (C. difficile) is a major pathogen causing antibiotic-associated diarrhea and pseudomembranous colitis, with Clostridioides difficile infection (CDI) showing a global upward trend. Significant differences exist in clinical manifestations and pathogenic potential among strains of varying virulence, yet their underlying metabolic basis and molecular mechanisms remain poorly understood. Systematic investigation of metabolic characteristics across strains with differing virulence levels is crucial for elucidating pathogenic mechanisms and identifying potential metabolic targets.

Methods: Four C. difficile strains with varying virulence gradients (RT027/ST1, RT046/ST35, RT017/ST37, RT012/ST54) were selected. Liquid chromatography-mass spectrometry (LC-MS)-based non-targeted metabolomics was employed, combined with principal component analysis (PCA), Partial Least Squares Discriminant Analysis (PLS-DA), and pathway enrichment analysis to compare metabolic differences among strains.

Results: A total of 3,255 metabolites were identified (1,735 in positive ion mode and 1,520 in negative ion mode). Multivariate statistical models revealed significant metabolic profile separation among the four strains. The highly virulent strain (ST1) exhibited significantly enhanced activation in lipid metabolism, bile acid metabolism, nicotinic acid/nicotinamide energy metabolism, and branched-chain amino acid fermentation pathways compared to the low-virulence strain (ST54). Analysis of virulence gradient-related metabolites identified 13 differentially expressed metabolites with potential biological significance, including upregulated isomangiferin, ginsenoside ro, glycocholic acid, lactic acid, isovalerate, and downregulated inosine, n-acetylmuramate, n-acetylglucosamine, cholesterol. These metabolites were primarily enriched in pathways involving bile acid synthesis, pyruvate metabolism, amino sugar and nucleotide sugar metabolism, and sterol biosynthesis.

Conclusion: This study systematically characterized the metabolomic profiles of C. difficile strains of different ST types, revealing that their enhanced virulence is closely associated with the reprograming of energy metabolism, membrane lipid structural remodeling, and bile acid metabolism. Metabolic differences suggest that highly virulent strains may enhance fermentation and lipid synthesis pathways to gain stronger survival and infection capabilities. The 13 candidate metabolites identified hold promise as potential biomarkers for distinguishing strain virulence levels, providing new theoretical basis for subsequent targeted metabolic regulation and anti-C. difficile therapies.

Psychrophilic anaerobic digestion (PAD) requires optimization to improve methane production at low temperatures (<20 °C). This study aimed to improve methane production via bioaugmentation with psychrotolerant Serratia marcescens (SM) and biostimulation with nano-additives, comprising calcium phosphate (CaP) and hematite (α-Fe₂O₃) nanoparticles (NPs), during batch PAD of cattle manure and food waste at 15 °C. The highest methane yields were obtained from treatment with SM and both NPs (163.9 ± 18.0 mL CH₄ g^-1 VS), thereafter with the combination of CaP and α-Fe₂O₃ NPs (143.9 ± 50.2 mL CH₄ g^-1 VS). The lowest yield was observed in the control (70.2 ± 4.9 mL CH₄ g^-1 VS) followed by treatment with SM alone (124.6 ± 20.3 mL CH₄ g^-1 VS). Treatment with CaP and α-Fe₂O₃ NPs reduced the lag phase more than the other treatments. Moreover, the addition of nano-additives biostimulated PAD without significantly altering the microbial community composition. The dominant genera included Bacteroides, Acinetobacter, and Methanosarcina (a mixotrophic methanogen) after batch PAD across all treatments. This research provides new insights on the augmentative effect of SM, CaP and α-Fe₂O₃ NPs on methane production and microbial community dynamics during PAD.

Aedes aegypti mosquitoes are principal vectors of arboviruses such as dengue, chikungunya, and Zika. The intracellular symbiont Wolbachia pipientis is known to inhibit viral replication and induce cytoplasmic incompatibility, making it a promising candidate for biological vector control. While Wolbachia is commonly found in Ae. albopictus, its natural presence in Ae. aegypti remains under debate, particularly in India. This study investigated the presence and diversity of Wolbachia in Ae. aegypti mosquitoes collected from 21 locations across Pune district, Maharashtra, during a 2024 arbovirus outbreak. A total of 1,020 adult mosquitoes and 1,000 larvae and pupae were morphologically and molecularly confirmed as Ae. aegypti and pooled (n = 93) for Wolbachia screening using 16S rRNA and wsp gene-specific PCRs. Positive samples were sequenced and subjected to phylogenetic and intergenomic similarity analyses. Simultaneously, dengue, chikungunya, and Zika virus screening was conducted via RT-qPCR. Entomological indices were calculated to assess vector density. Wolbachia was detected in 11.8% of Aedes aegypti pools. Phylogenetic and similarity analyses identified three distinct clusters: supergroup A (n = 2), B (n = 5), and a divergent F-type strain (n = 2). Nucleotide gene sequence similarity analysis corroborated the phylogenetic structure, showing high intra-supergroup similarity and low inter-supergroup similarity, consistent with deep evolutionary divergence among supergroups. Supergroup A and B sequences exhibited close affinity to known wAlbA and wAlbB lineages, respectively, whereas the F-type sequence formed a distinct cluster with low intergenomic similarity to A and B members, indicating a divergent lineage. Dengue virus RNA was detected in two pools, one co-occurring with Wolbachia, although individual co-infection could not be confirmed. This study provides the first evidence of naturally occurring Wolbachia supergroups A, B, and a potentially novel F-type in Ae. aegypti from an arbovirus-endemic region of western India. These findings highlight the evolutionary diversity of Wolbachia in local vector populations and underscore the importance of integrating Wolbachia surveillance into vector control strategies.