Frontiers in Microbiology最新文献

Introduction: The growing demand for plant-based functional foods has driven research into non-dairy fermented alternatives that can deliver live microorganisms and potential health benefits. The pseudocereal Quinoa is a substrate of interest for lactic acid fermentation. This study aimed to develop a fermented quinoa-based beverage using autochthonous lactic acid bacteria (LAB) strains with technological and functional potential.

Methods: Six LAB strains previously isolated from plant sources were screened for growth kinetics in an animal-free medium and in quinoa extract (QE). Lactiplantibacillus plantarum LpAv and Limosilactobacillus fermentum Lf2, an exopolysaccharide (EPS)-producing strain, were selected for beverage development. Fermentation parameters, rheological and biochemical profiles, peptide release, and sensory attributes were evaluated. An animal trial assessed immunomodulatory and antioxidant capacity in BALB/c mice that received fermented QE.

Results: Both strains were able to acidify QE to pH < 4.5 within 8 h, ensuring microbiological safety. EPS production by Lf2 improved viscosity and texture, while mixed fermentation enhanced lactic acid yield and impacted on peptidic profiles, indicating synergistic proteolytic activity. LAB remained viable (>8 log CFU/mL) after 28 days at 4 °C. Sensory testing (n = 111 participants) showed moderate acceptability, improved by artificial flavoring. In mice, fermented QE increased intestinal IL-10 and IFN-γ levels and elevated hepatic catalase and superoxide dismutase activities, suggesting antioxidant and immune-modulatory effects without bacterial translocation.

Conclusion: This work demonstrates the feasibility of producing a safe, stable, and functionally active fermented quinoa beverage using locally sourced LAB. The combination of L. plantarum LpAv and L. fermentum Lf2 improved both technological and functional properties, supporting their potential as starter cultures for plant-based probiotic foods.

Enteric methane from ruminants is a major source of greenhouse gasses (GHG) emissions globally, and its formation also leads to a decrease in animals' productivity due to loss of dietary energy. Reducing enteric methane emissions is essential for mitigating greenhouse gas-driven climate changes while simultaneously enhancing ruminant production efficiency. Methanogens residing in the rumen are responsible for enteric methane production. They reduce carbon dioxide to methane with the help of hydrogen, thus playing a crucial role in global methane emissions. Methyl coenzyme M reductase (MCR) is a key enzyme in methanogens that catalyzes the final step of methanogenesis. This review consolidates information on MCR enzyme's structure, cofactor chemistry, and post-translational modifications (PTMs), followed by a critical appraisal of inhibition strategies using synthetic compounds like 3-nitrooxypropanol (3-NOP) and bromoethanesulfonate (BES) along with their mode of action. Modern in silico studies for the identification of novel natural MCR inhibitors have also been discussed. Blocking MCR through synthetic or natural compounds is a promising approach for mitigating methane emissions from ruminants, allowing the rest of the rumen's microbial community to function normally. By specifically blocking MCR, hydrogen and other byproducts of carbohydrate fermentation are still consumed, allowing the animal's digestion and productivity to remain unaffected while significantly reducing its contribution to greenhouse gas emissions. Making it a target, the issue of methane emission in ruminants can be solved without affecting the overall rumen microbiota. Moreover, challenges (hydrogen accumulation, cost, and regulatory hurdles) and emerging opportunities regarding MCR inhibitory strategies are proposed to guide targeted research for scalable methane mitigation in ruminants.

Microbes associated with plants have proven to play a fundamental role in their growth and phytosanitary status. Microbial community architecture and function results from interactions with the host and with each other. Therefore, microbial diversity and the array of possible interspecies interactions should be considered as key elements for the development of future biocontrol and crop improvement strategies. To gain some insight into this potential, we isolated 16 rhizospheric and 16 endophytic bacteria from sugarcane and tested their ability to interact with each other. To this end, we performed 120 pairwise interaction assays within each group. Although most interactions were neutral in both rhizospheric and endophytic communities, negative interactions were more frequent between rhizospheric isolates. In contrast, positive ones predominated among endophytic isolates. After determining the interaction phenotypes between isolates, we tested their impact on plant growth promoting (PGP) traits and biocontrol against Xanthomonas albilineans. Our results demonstrate that interspecies interactions among sugarcane-associated bacteria can modulate key PGP traits regardless of their interaction phenotype, highlighting a potentially overlooked layer of functional regulation within the microbiome. Accordingly, social behavior of microorganisms might set the basis for a rational design of performance-improved bioinoculants for agriculture, particularly consortia-based inoculants.

[This corrects the article DOI: 10.3389/fmicb.2025.1692179.].

Pramanicin is a fungal metabolite with notable biological activities, including antifungal and anticancer properties. While its chemical synthesis has been achieved, its biosynthetic pathway has remained elusive. Here, we report the identification of the pramanicin biosynthetic gene cluster from the fungus Macrophomina phaseolina. Heterologous expression in Aspergillus nidulans demonstrated that the hybrid polyketide-nonribosomal (PKS-NRPS) enzyme PraA synthesizes a linear precursor that cyclizes to form pre-pramanicin. The flavin-dependent monooxygenase PraD and short-chain dehydrogenase/reductase PraB subsequently catalyze a hydroxylation and ketoreduction to yield pramanicin-A. Notably, we established that the final epoxidation step requires the PraC-a membrane-integrated protein of the previously uncharacterized DUF2306 family. This represents the first functional assignment of a DUF2306 family protein in natural product biosynthesis. Combinatorial expression and in vivo feeding experiments confirmed that PraC is essential for the formation of the bioactive epoxide moiety in pramanicin. Our work deciphers the biosynthetic pathway of a pharmaceutically relevant natural product, expands the enzymatic toolbox for synthetic biology by characterizing a novel family of membrane-associated biosynthetic enzymes.

Background: Pseudomonas juntendi is an emerging opportunistic pathogen first described in 2019, whose antimicrobial resistance mechanisms and clinical significance remain poorly understood. In this study, we report the first urinary isolate of P. juntendi (PJ1) co-harboring bla _NDM-1 and bla _IMP-15, and comprehensively analyzed its phylogeny, resistance architecture, and biological characteristics.

Methods: Species identification and phylogenetic placement were determined using whole-genome sequencing and average nucleotide identity analyses. Genomic annotation was applied to resolve the structure of resistance islands. Biofilm formation, stress tolerance, and virulence were assessed through crystal violet staining, environmental stress assays, and Galleria mellonella infection models, respectively.

Results: Phylogenomic analysis revealed that PJ1 clustered with isolates from China and Japan, forming an East Asian lineage suggestive of regional dissemination. Genomic analysis showed that PJ1 carries two metallo-β-lactamase modules integrated into the chromosome: bla _NDM-1 embedded within an ICE-IS91 composite island and bla _IMP-15 located in an integron-Tn402-like module, representing a mosaic multidrug resistance island. Phenotypically, PJ1 exhibited robust biofilm formation, tolerance to bile salts and hyperosmotic stress, and high virulence in the G. mellonella model.

Conclusion: PJ1 represents the first urinary P. juntendi isolate carrying both bla _NDM-1 and bla _IMP-15 on a single chromosome. Its composite resistance island and strong colonization capacity suggest that P. juntendi may serve as an emerging reservoir for metallo-β-lactamase dissemination, posing potential clinical and epidemiological threats.

"Candidatus Liberibacter asiaticus" (CLas) is an uncultivable α-proteobacterium causing the most destructive and currently incurable citrus disease, Huanglongbing (HLB). The transcription factors (TFs) of CLas are involved in various biological processes. However, the functions of most TFs remain unverified. BolA is reported to be an important transcriptional regulator related to bacterial growth and virulence. Here, the role of BolA in CLas was investigated using gene deletion and complementation assays in the heterologous host Sinorhizobium meliloti (Sme). The results showed that BolA _CLas and BolA_Sme are similar in sequence and transcriptional regulation. BolA positively regulates biofilm formation-evidenced by the significant downregulation of a key gene (cyaA) in the mutant (ΔBolA_Sme ), without affecting bacterial growth. The upregulation of 16 differentially expressed genes (DEGs) related to flagellar assembly indicated that BolA negatively regulates CLas motility. BolA deletion also led to the downregulation of ABC transporters (15 DEGs) and lipid metabolism genes (13 DEGs), correlating with reduced stress tolerance. Furthermore, BolA _CLas is involved in modulating heme metabolism, as well as protein export, folding, sorting, and degradation. Finally, in vivo screening identified two compounds as BolA inhibitors, which significantly reduced CLas titer in infected periwinkle leaves. Taken together, this study constitutes a relevant step toward the understanding of CLas virulence by demonstrating that BolA is a key TF involved in biofilm formation, stress response, motility, and bacterial physiology, thereby presenting a potential target for disease control.

Bioremediation of uranium-contaminated environments using native bacteria shows great promise. While Shewanella putrefaciens (S. putrefaciens) is a known uranium reducing bacterium, the mechanisms and adaptability of indigenous strains from uranium mine tailings remain unexplored. This study isolated a dominant indigenous strain of S. putrefaciens and employed a combined genomic and spectroscopic approach to elucidate its unique uranium fixation mechanism. Microbial diversity analysis confirmed the dominance of Shewanella in the oligotrophic and radioactive tailings. Whole-genome sequencing revealed a significant enrichment of genes related to energy metabolism and stress resistance, providing a genetic basis for its survival and activity. Crucially, by combining advanced spectroscopic techniques with an MtrA gene knockout experiment, we deciphered the specific role of the Mtr pathway in extracellular electron transfer for uranium reduction. Remarkably, the isolated strain achieved a uranium removal efficiency of up to 93% under experimental conditions, demonstrating its high potential for uranium bioremediation. This work not only provides a robust indigenous candidate for bioremediation but also delivers novel mechanistic insights into the uranium transformation processes of indigenous Shewanella, advancing strategies for the application of tailored microbiomes in radioactive waste management.

Introduction: Ulcerative colitis (UC) is a chronic inflammatory disorder of the colon with rising incidence and limited therapeutic options. Probiotics are increasingly recognized as potential interventions, but strain-specific differences remain insufficiently defined.

Methods: We conducted a meta-analysis of publicly available microbiome datasets to characterize disease-associated dysbiosis, focusing on the genus Lactobacillus. We then evaluated Lactobacillus paracasei WIS43, a novel strain isolated from the breast milk of a healthy volunteer, in a dextran sulfate sodium (DSS)-induced murine colitis model, using mesalazine and the commercial strain Lactobacillus paracasei LPC-37 as comparators. Disease severity, histopathology, inflammatory cytokines, and gut microbiota composition were systematically assessed.

Results: Meta-analysis confirmed a significant depletion of Lactobacillus in UC patients. In vivo, WIS43 treatment reduced body weight loss, disease activity index scores, and colon shortening. Histological analysis revealed preserved epithelial integrity and reduced inflammatory infiltration. WIS43 significantly decreased serum and colonic TNF-α, IL-6, and IL-1β levels, demonstrating stronger anti-inflammatory activity than LPC-37 and comparable efficacy to mesalazine. 16S rRNA sequencing further showed that WIS43 restored beneficial taxa, including Lactobacillus johnsonii and Lactobacillus taiwanensis, while reducing potentially pathogenic bacteria.

Conclusion: These findings identify WIS43 as a promising probiotic candidate for the prevention and treatment of UC, supporting its therapeutic potential through coordinated modulation of host immunity and gut microbiota.

Introduction: This study investigated the dose-response efficacy of dietary oregano essential oil (OEO) in mitigating severe heat stress (THI ≈ 86) in beef cattle.

Methods: Thirty-six Pinan bulls were fed a basal diet alone (control) or supplemented with 7 (L-OEO) or 14 g/d (H-OEO) of OEO for 60 days.

Results: The low-dose OEO (7 g/d) significantly improved hepatic function (reduced ALT, AST; increased ALB, TP), enhanced immune (increased IgA, IgM) and antioxidant status (decreased MDA, increased SOD, CAT), and increased the ruminal abundance of Bacteroidota and Prevotella, which correlated negatively with acyl-glycine metabolites. In contrast, the high dose (14 g/d) only increased GSH-Px and T4, resulted in higher MDA than L-OEO, and did not significantly affect the rumen microbiota.

Conclusion: Supplementation with 7 g/d OEO optimally improved overall health and metabolic function in heat-stressed bulls, whereas a 14 g/d dose offered no additional benefits.