Frontiers in Microbiology最新文献

Introduction: C1 gas bioconversion for single-cell protein (SCP) production offers dual environmental benefits by mitigating greenhouse gases and generating protein resources. This study systematically determined optimal methane-to-air ratios (CH₄:air, v/v) for enhancing methane-oxidizing bacteria (MOB) growth and SCP yield under three distinct nitrogen assimilation modes: nitrate-driven pMMO expression, ammonium-driven sMMO expression, and nitrogen-fixing sMMO expression.

Methods: Experiments were conducted under three nitrogen assimilation regimes: nitrate-fed pMMO expression, ammonium-fed sMMO expression, and nitrogen-fixing sMMO expression systems. By adjusting the volumetric ratio of methane to air, the effects on bacterial growth, biomass accumulation, specific growth rate, and key enzymatic activities were evaluated. Measured parameters included OD₆₀₀, cell dry weight, specific growth rate (μ_max), and nitrogenase activity in the nitrogen-fixing system. Data from repeated measurements were subjected to statistical analysis to clarify the regulatory role of gas ratios on metabolic pathways.

Results: In the nitrate-fed pMMO expression system, a CH₄:air ratio of 1:3 yielded optimal growth, with an OD₆₀₀ of 1.11, cell dry weight of 0.44 ± 0.023 g/L, and μ_max of 0.022 h^-1. Similarly, the ammonium-fed sMMO expression system achieved best performance at the same ratio (OD₆₀₀ 1.19, biomass 0.56 ± 0.014 g/L, μ_max 0.025 h^-1). In contrast, the nitrogen-fixing sMMO expression system performed better at a lower oxygen ratio (CH₄:air = 1:2), reaching an OD₆₀₀ of 0.62, biomass of 0.28 ±0.008 g/L, nitrogenase activity of 1.09 nmol/(min mg protein), and μ_max of 0.016 h^-1).

Discussion: The results reveal oxygen's critical dual role: higher O₂ levels enhance methane oxidation by activating the copper-dependent catalytic site of pMMO but simultaneously and irreversibly damage the oxygen-sensitive nitrogenase ssential for N₂ fixation, suppressing its activity. Conversely, lower O₂ protects nitrogenase but limits pMMO efficiency. This creates a fundamental metabolic trade-off where the optimal CH₄/O₂ ratio balances these opposing effects, strategically partitioning cellular energy either toward efficient methane assimilation (favored by higher O₂) or toward the ATP-intensive process of nitrogen fixation (requiring lower O₂). These identified gas-ratio thresholds provide actionable parameters for designing scaled SCP bioproduction systems, enabling effective coupling of industrial methane mitigation with sustainable protein synthesis through gas-phase engineering.

Methylmercury (MeHg), a bioaccumulative neurotoxic heavy metal, substantially threatens environmental and human health. In natural environments, MeHg formation and degradation are primarily mediated by microorganisms containing hgcAB, merA, or merB genes. However, these genes have not been simultaneously analyzed in open-ocean samples. This study aimed to investigate the distribution and phylogeny of functional genes associated with mercury (Hg) methylation (hgcA and hgcB), demethylation (merB), and reduction (merA), as well as dissolved total Hg (THg) and MeHg concentrations in the western North Pacific Subtropical Gyre (WNPSG) using metagenomic analysis. Although THg levels varied across sampling sites, MeHg concentrations consistently increased with depth. A strong correlation between dissolved MeHg and apparent oxygen utilization indicated a link between Hg methylation and microbial respiration. hgcA, merB, and merA were predominantly detected at depths of 500-1,500 m, where MeHg concentrations peaked, indicating active microbial Hg speciation within mesopelagic layers. A higher abundance of hgcA than merB suggests that microbial Hg methylation may surpass demethylation in this region. Phylogenetic analyses of hgcAB identified the Nitrospina lineage as dominant Hg methylators. Metabolic pathway analyses of metagenome-assembled genomes (MAGs) showed that Nitrospina harboring hgcAB possesses the nitrite reductase pathway, suggesting a linkage between Hg methylation and nitrogen cycling. MAGs with hgcA affiliated with Myxococcota (Deltaproteobacteria) exhibited a strong association with sulfur cycling. Diverse lineages harboring merB and merA genes were identified, suggesting that MeHg demethylation and Hg(II) reduction likely co-occur. Methanogenesis pathways in some Alphaproteobacteria with merB or merA suggest a potential connection between methane production and MeHg degradation and Hg(II) reduction. These findings provide novel insights into the intricate interactions between microbial communities, functional gene distributions, and Hg biogeochemical cycling in the WNPSG.

Background: Lycopene, a vital antioxidant, can reduce oxidative damage to cells caused by reactive oxygen, prevent cancer, lower blood cholesterol levels, and mitigate cardiovascular diseases. We screened a lycopene-producing strain of the genus Polymorphospora, designated A560, and discovered that its metabolic pathway lacks the lycopene β-cyclase gene crtY, which is responsible for converting lycopene into β-carotene. The absence of crtY alleviates the challenges associated with the addition of a cyclooxygenase inhibitor, which previously hindered the large-scale accumulation of lycopene in Blakeslea trispora.

Method: This study was conducted to enhance lycopene production in strain A560 through a multi-stage optimization strategy, focusing on improving extraction efficiency and optimizing culture medium components. The extraction conditions were optimized by testing different solvent systems (acetone/n-hexane/ethanol), extraction temperatures, and durations. Subsequently, a uniform design (UD) was applied to systematically optimize the composition of the culture medium to maximize lycopene yield.

Results: The extraction conditions were systematically optimized. A crushing duration of 4 min was identified as optimal for complete cell disruption. The most efficient solvent system was determined to be n-hexane/ethanol (2:1, v/v) at 60 °C, which yielded 62.05 ± 4.68 mg/L of lycopene-a 37.13% increase over extraction with acetone at room temperature (45.25 ± 0.98 mg/L). Subsequent medium optimization through a uniform design revealed that soluble starch and glycerol were critical components. Cultivation in the theoretically optimized medium predicted by the model resulted in a lycopene yield of 142.54 ± 8.58 mg/L. Finally, regulating the oxygen supply by adjusting the flask's volume of air to a medium volume (Va/Vm) ratio proved crucial. The highest lycopene production of 201.44 ± 6.23 mg/L was achieved at a Va/Vm ratio of 1.5, which marks a 224.64% improvement over the yield obtained after the initial extraction optimization (62.05 ± 4.68 mg/L).

Conclusion: The extraction and fermentation processes for lycopene production in Polymorphospora sp. A560 were successfully optimized, resulting in significantly enhanced yields. These results demonstrate that strain A560 is a promising microbial resource for the fermentative production of lycopene.

[This corrects the article DOI: 10.3389/fmicb.2023.1252785.].

Introduction: Microbial additives can improve silage quality in lowland areas. However, Saccharomyces cerevisiae and Lactic Acid Bacteriacan efficacy on whole-plant maize silage under Tibet's hypoxic and cold environment, have not been explored.

Methods: In this experiment, whole corn plants cultivated in Dazi District, Lhasa City, Xizang (Tibet) Autonomous Region, were selected as silage raw materials. The treatment group was added 0.5 kg of microbial additives per ton of silage. The addition levels for both Saccharomyces cerevisiae and Lactic Acid Bacteria were ≥ 1 × 107 CFU·g-1 FM). The quality of silage and its in vitro fermentation characteristics were determined on 0, 30 and 60 days of fermentation, respectively. Subsequently, dairy cows were fed with silage after 60 days of fermentation to evaluate milk production and milk quality.

Results: The results indicated that the lactic acid content in the treatment group was increased significantly on 30 and 60 days of fermentation (p < 0.05). In addition to Simpson's index, alpha diversity was significantly affected by the fermentation day × treatment interaction (p < 0.05). At 60 days of fermentation, the abundance of Firmicutes phylum in the treatment group was significantly higher than that in the control group (p < 0.05). The abundance of genera such as Acetobacter and Latilactobacillus was significantly decreased (p < 0.05), while the abundance of the genus Weissella was significantly increased (p < 0.05). Dairy cows were fed 60-day maize silage, the milk protein content and total solid content in the treatment group were significantly higher than that in the control group (p < 0.05). The levels of dry matter degradation rate, ammonia nitrogen and total volatile fatty acids in the in vitro fermentation of maize silage in the treatment group on the 60th day of fermentation were significantly higher than that in the control group (p < 0.05).

Conclusion: In Xizang (Lhasa, China), the addition of microbial additives has significantly improved the quality and nutritional value of whole corn silage plants and enhanced the milk quality of local dairy cows. This provides a theoretical basis for the application of microbial additives from the Qinghai-Tibet Plateau to agricultural crops.

Background: Helicobacter pylori (H. pylori) is a major gastric pathogen and class I carcinogen that causes chronic gastritis, peptic ulcer, and gastric cancer if left untreated. However, evidence on H. pylori prevalence and antimicrobial resistance in Kazakhstan, a country with a high gastric cancer burden, remains scarce. This study presents the first culture-based epidemiological investigation of H. pylori at a single center in Almaty.

Materials and methods: We conducted a cross-sectional study (2024-2025) of 150 dyspeptic patients in Almaty, Kazakhstan. A subset (n = 148) underwent rapid stool antigen (RAS) testing before gastric biopsy collection. Biopsy samples were cultured, and 86 (57.3%) yielded viable H. pylori isolates. Antimicrobial susceptibility testing by the agar dilution method was performed on these 86 isolates. Demographic and clinical data were analyzed, and a regional meta-analysis was conducted using data from recent studies across Central Asia and Russia to estimate pooled prevalence and clarithromycin resistance.

Results: Among 148 patients tested by RAS, 137 were positive. Resistance rates among 86 isolates were 87.2% to metronidazole, 33.7% to clarithromycin, and 3.5% to amoxicillin; no resistance was detected to minocycline or sitafloxacin. Multidrug resistance (defined as resistance to two or more antibiotics) was observed in 34.8% of isolates. The pooled H. pylori prevalence across Central Asian studies was 70% (95% CI: 59-80%), and pooled clarithromycin resistance was 29% (95% CI: 10-53%).

Conclusion: This study provides the first culture-based evidence of H. pylori infection and antimicrobial resistance in Kazakhstan. The high resistance to metronidazole and clarithromycin suggests a likely lower success of standard triple therapy in Almaty. Absence of resistance to minocycline and sitafloxacin supports their use in rescue regimens. These findings highlight the urgent need for national surveillance, updated treatment guidelines, and integration of molecular resistance monitoring to improve evidence-based management of H. pylori in Central Asia.

In the environment, Vibrio cholerae employs multiple strategies to resist predation by heterotrophic protozoa. For example, V. cholerae biofilms release toxic compounds, such as ammonium and pyomelanin, which can kill protists, such as Tetrahymena pyriformis. V. cholerae has also been shown to survive intracellularly and can escape as viable cells inside protozoan-expelled food vacuoles (EFVs). We previously reported that V. cholerae encased in EFVs are hyperinfectious, establishing an important link between anti-protozoal strategies and bacterial virulence. Although the intracellular resistance and escape of V. cholerae in EFVs have been reported, the molecular mechanisms behind this remain poorly understood. Here, we used single-cell transcriptomics of V. cholerae exposed to T. pyriformis and captured a total of 5,344 bacterial cells with heterogeneous gene expression. Cells with the same pattern of gene expression were grouped, resulting in 11 clusters of cells with a unique gene expression profile. Genes encoding outer membrane proteins, F₁F₀-Na⁺/H⁺ ATPase, metabolites, and toxins showed differential expression among the clusters. Furthermore, the motility-associated killing factor (Mak) toxins were differentially expressed. The V. cholerae mutants ΔmakA, ΔmakB, and ΔmakE were not capable of killing T. pyriformis, and ΔmakA and ΔmakE showed reduced survival inside EFVs compared to the wild type. These findings identify Mak toxins as key mediators of V. cholerae resistance to protozoan grazing and survival within EFVs. More broadly, our results provide mechanistic insight into grazing resistance, reveal factors facilitating persistence in EFVs, and underscore the interplay between environmental survival strategies and virulence in pathogenic bacteria.

To evaluate the biocontrol potential of the cell-free fermentation filtrate (CFFF) of Bacillus atrophaeus strain YL84 against Fusarium oxysporum f. sp. vasinfectum (FOV), this study systematically investigated the effects of the CFFF at various dilution ratios on FOV mycelial growth, conidial germination, cellular nucleic acid leakage, and malondialdehyde (MDA) content. Furthermore, the environmental stability of its antifungal activity was assessed. In addition, a dual-culture assay was conducted to evaluate the antagonistic activity of strain YL84 against FOV. The results of the dual-culture assay showed that strain YL84 significantly inhibited the growth of FOV, with an inhibition rate of 81.06%. Subsequently, the YL84 CFFF exerted significant inhibitory effects on FOV mycelial growth and conidial germination across different concentrations, achieving maximum inhibition rates of 75.68% and 77.56%, respectively. Notably, the treated mycelia exhibited a significant increase in cellular nucleic acid leakage and elevated levels of MDA, a product of lipid peroxidation, suggesting that the CFFF may disrupt the integrity of the pathogen's cell membrane. Stability assays revealed that the CFFF possessed substantial tolerance to high temperatures, ultraviolet irradiation, and hypersaline environments, although it remained sensitive to strongly alkaline conditions. Greenhouse pot experiments further confirmed the efficacy of YL84 CFFF in controlling cotton Fusarium wilt, with a maximum control efficacy of 69.21%. Moreover, the treatment induced the upregulation of defense-related enzyme activities in the plants, suggesting that the CFFF may function through both direct antifungal action and the elicitation of host-induced resistance. Component identification via Ultra-Performance Liquid Chromatography-Ion Mobility-Quadrupole Time-of-Flight Mass Spectrometry (UPLC-IMS-Q-TOF-MS) suggested that the filtrate is rich in structurally diverse compounds that were putatively identified as potential antimicrobial substances, predominantly classified as terpenoids and their derivatives. In conclusion, this study provides a systematic evaluation and supporting evidence for the further development of B. atrophaeus YL84 as a biocontrol agent.

Background: Mulberry leaf (Morus alba L.) is an edible plant that has been found to have medicinal effects in the treatment of hyperuricemia (HUA). The bioactive compounds of mulberry leaf and their mechanisms of action have not been determined yet.

Methods: In-silico methodologies were used to identify bioactive compounds and to determine the underlying mechanisms of mulberry leaf. In order to verify the biochemical mechanism and intestinal microbiota, in vivo experiments were conducted.

Results: Kaempferol was identified as the principal bioactive compound, while the key targets were AKT1 and TNF. Molecular docking and dynamics simulations revealed that AKT1-kaempferol and TNF-kaempferol complexes showed strong and stable binding pattern after a 100 ns simulation. In vivo studies demonstrated that kaempferol exerted significant anti-HUA effects. Specifically, kaempferol reduces AKT expression and phosphorylation, which may in turn reduces the oxidative stress and inflammatory pathways and signal transmission of the kidneys. Meanwhile, the application of kaempferol attenuated gut microbiota dysbiosis caused by HUA.

Conclusion: Kaempferol may regulate UA metabolism and inflammatory injury by modulating the AKT signaling pathway, and exert its effects on the gut-kidney axis and restoring gut microbiota composition.