[Objective] To screen the indigenous functional microorganisms in reservoirs and explore their oil recovery mechanisms, we conducted field tests to determine the process and technical feasibility of enhancing crude oil recovery by indigenous microorganisms. [Methods] We collected samples from the Yingdong Oilfield and used oil plates to screen for the target bacteria. Next, we evaluated the environmental adaptability and optimized the culture conditions of the strain. Further, we measured the emulsifying, viscosity-reducing, paraffin-resistant, and hydrocarbon conversion abilities of the isolate to evaluate the oil recovery competence of the strain and explored its oil recovery mechanism. Finally, we carried out the microbial enhanced oil recovery tests in the oilfields. [Results] We isolatedBacillus velezensis B6 from the oil-water sample with an emulsifying activity index (EI24) of 100.00%, a viscosity reduction rate of 97.20%, and a paraffin resistance rate of 86.90%, which indicated that strain B6 had good emulsifying and viscosity-reducing abilities and improved oil recovery potential. Strain B6 could reduce heavy components in crude oil and increase light hydrocarbons to improve crude oil properties and quality. Moreover, we carried out single-well huff and puff and paraffin removal operations in Yingdong Oilfield, Yuejin Oilfield, and Huatugou Oilfield with a total of 62 well-times in the field test, which resulted in a cumulative oil increase of 1 460.36 tons and an average delay of 47 days in the well flushing cycle. The economic benefit was CNY 3.425 million, and the input-output ratio was 1:4. [Conclusion] The laboratory studies and field tests proved that indigenousB.velezensis B6 can significantly improve the oil recovery and well paraffin removal, with great application potential.

[Objective] To study the effect of hydrogen peroxide (H₂O₂) treatment on biogas production of vitrinite from coal. [Methods] Shengli lignite collected from Inner Mongolia was used in this study. The methanogenic microbial consortium previously enriched and preserved in our laboratory was used as the inoculum. Coal macerals were separated by floatation, which yielded three samples containing high vitrinite (GJ), medium vitrinite (ZJ), and low vitrinite (DJ). After being characterized, the samples were treated with 10% H₂O₂ for 30 days at a solid-to-liquid ratio of 1:15. Biogas production experiments were conducted with the coal samples before and after treatment. Gas chromatography was employed to analyze the gas composition, and X-ray diffractometry and Fourier transform infrared spectroscopy were employed to study the physical and chemical properties of the coal before and after treatment as well as after gas production. [Results] The coal samples after H₂O₂ treatment showcased reduced vitrinite content and carbon fixation and increased volatile matter. The reaction was more intense in the coal sample with high content of vitrinite, accompanied by increased oxygen content and reduced carbon. Methane yields from untreated coal samples on day 100 followed the order of GJ (174.24 μmol/g coal)>ZJ (164.31 μmol/g coal)>DJ (135.52 μmol/g coal). However, the coal samples pretreated with H₂O₂ ceased gas production after day 20, with the gas yields of 39.63, 39.61, and 41.55 μmol/g coal, respectively, representing reductions of 77.26%, 75.89%, and 69.34%, respectively, compared with those from the coal samples without treatment. Furthermore, as vitrinite content increased, the coal samples demonstrated decreased layer spacing (d₀₀₂) of the aromatic ring lamellae, ductility (L_a) of the single-layer lamellae, and stacking degree (L_c) of the lamellae and increased number of aromatic layers (N) after H₂O₂ treatment, which indicated that the crystal nuclei appeared smaller. In addition, H₂O₂ treatment led to increased proportions of aromatic carbons, aromatic moieties, C=O groups, and C=C groups, enhanced aromatic ring condensation, and increased number of oxygen-containing functional groups. [Conclusion] Long-term H₂O₂ treatment reduces organic matter that is readily bioavailable in coal matrix, thereby decreasing gas production.

[Objective] To investigate the effects of hydrogen peroxide treatment on the physicochemical properties and biogas production of lignite. [Methods] We carried out orthogonal experiments to optimize the conditions of hydrogen peroxide pretreatment for Shenli No.5 lignite. Lignite was treated under the optimal conditions to obtain coal residues and treatment solutions. The physicochemical properties, including elemental and maceral composition, mineral components, microcrystalline structure, porosity, permeability, surface morphology, organic functional groups, and organic composition in the treatment solution were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), brunauer-emmett-teller (BET), gas chromatography-mass spectrometry (GC-MS), and high-performance liquid chromatography (HPLC). The physicochemical properties were then compared among the raw coal, treated residue, and treatment solution. [Results] The optimal pretreatment conditions of lignite were treatment with 5.0% hydrogen peroxide at a liquid-to-solid ratio of 30:1 for 20 days, under which the total organic carbon yield in the treatment solution was 105 mg/L. After treatment under these optimal conditions, the treated residue exhibited increased cracks and dents on the surface and loosened surface structures. In addition, the interlayer spacing of the aromatic plains of the coal increased while the aromatic ring structure became more open with smaller crystal nucleus structures. Both porosity and specific surface area increased after the treatment. Compared with that before treatment, the treated residue showcased decreased fixed carbon, carbon, and vitrinite and increased ash, volatile matter, oxygen and hydrogen, and inertinite. The content of functional groups such as O=C−O, C=C, and C=O increased in the treated residue, while that of N−H and C−H reduced. The biogas production of the treatment solution and the treated residue was 39.13% and 94.46%, respectively, lower than that of raw coal. Hydrogen peroxide pretreatment primarily acted on vitrinite, dissolving organic carbon and altering the functional groups of large molecular structures in coal. This altered the aromatic ring structure of coal, causing small molecules to dissolve into the treatment solution under oxidative conditions. The organic compounds in the treatment solution mainly consisted of short-chain fatty acids. After biogas production, the number of low-molecule-weight acids and organic compounds decreased in the treatment solution. The relative abundance of dominant microbial phyla and genera varied significantly among different microcosms. Regarding the archaea for biogas production, the dominant phylum and genus wereHalobacteriota andMethanosarcina in the raw coal andThermoproteota andBathyarchaeia in the treatment solution, respectively. In terms of the bacteria for biogas production, the dominant phylum and genus wereActinomycetota andGaiellales in the raw coal andPseudomonadota andDelftia in the treatment solution, respectively. [Conclusion] The organic carbon dissolved from coal can be utilized by microorganisms for biogas production. However, the removal of organic components by over-oxidation may decrease the biogas production.

[Objective] Methane-oxidizing bacteria (MOB) are crucial indicators in the microbial exploration of oil and gas reservoirs, while their diversity and distribution are influenced by geographical location and environmental factors. This study aims to explore the effects of environmental variations on the abundance and distribution of MOB in the soil samples collected from seven representative areas in typical oil and gas reservoirs. [Methods] Soil samples were subjected to real-time fluorescence quantitative PCR (qPCR) forpmoA and sequencing of bacterial 16S rRNA gene andpmoA. The abundance of MOB was compared among different samples, on the basis of which the impacts of environmental factors on the distribution of MOB were analyzed. [Results] The highest water content (approximately 22.8%) was detected in the samples from the Jianghan Basin. The average content of nitrate nitrogen was highest in the Yubei oil field, reaching approximately 31.96 μg/g. The Chunguang oil field showcased the highest concentrations of SO₄²⁻ (6 425.0 mg/g) and Cl⁻ (1 617.0 mg/g). The qPCR results revealed that thepmoA in MOB accounted for only 0.77% of that in total soil bacteria, indicating the low absolute abundance of MOB in the soil. The 16S rRNA gene sequencing identified three type Ⅰ MOB genera (Methylosarcina,Methylocaldum, andMethylococcus) and one type Ⅱ MOB genera (Methylocystis). However, the dominant genera in the MOB had extremely low relative abundance, with the maximum of 0.124%. Sequencing ofpmoA revealed thatMethylocystis andMethylosinus, two genera of type Ⅱ MOB, were dominant. The absolute abundance of MOB showed significant correlations with ammonium nitrogen, pH, particle size, SO₄²⁻, and Cl⁻. The relative abundance of MOB had significant correlations only with particle size, total nitrogen, total phosphorus, and metal ions (Al, Fe, K, Ca, Mg, Mn, Zn, and Cu). The discriminant correlation analysis (DCA) indicated that soil moisture, pH, soil particles<2 μm, total nitrogen, and Ca²⁺ significantly influenced the composition of the functional genepmoA in MOB. [Conclusion] This study analyzed the absolute and relative abundance of MOB in soil samples from seven typical oil and gas reservoirs. The MOB abundance showed significant differences depending on the measurement method used. The 16S rRNA gene sequencing fails to comprehensively reflect the community structure of MOB in the soil samples. Different geographical locations showed variations in MOB communities, and no specific indicator communities were detected for oil and gas reservoirs or background sites on a national scale. The correlation analysis between environmental factors and MOB revealed that the environmental factors had different effects on the absolute and relative abundance of MOB.

[Objective] Microbial prospecting for oil and gas, characterized by high resolution, high signal-to-noise ratio, minimal environmental interference, low costs, and short time consumption, garners increasing attention from exploration experts. However, in most cases, microbial prospecting is based on laboratory culture and analysis, which cannot accurately and comprehensively reflect thein-situ dynamic changes of microbiota in oil and gas resources in the geological history. In this study, we compared the microbial community structure and developmental characteristics between the gas-producing zone and the background zone in Hangjinqi Gas Field, aiming to identify the surface microbial anomalies related to oil and gas. [Methods] We conducted the bacterial 16S rRNA gene sequencing for the soil samples collected from Xinzao and Shiguhao areas of Hangjinqi. Furthermore, we compared the microbial diversity, analyzed the impacts of physicochemical parameters on microbial distribution, and identified microbial anomalies. The co-occurrence network analysis was employed to explore the assembly process and functional composition of microbial community in the surface soil above the reservoir. [Results] In the Hangjinqi area,Actinobacteria andProteobacteria were dominant, accounting for 72.47% of the total microbial abundance. The correlation analysis of environmental factors with microbial abundance showed that the distribution of microorganisms in this area was not significantly correlated with environmental factors. The microbial community structure presented significant differences between the gas-producing area and the background area. The co-occurrence network analysis of the gas-producing area revealed non-randomness and connectivity in the microbial community, indicating deterministic factors play a dominant role in the construction of microbial communities. Modular co-occurrence network analysis revealed the formation of specific functional modules within the microbial community, and different modules possibly served different functions. [Conclusion] By comparing the microbial diversity between the gas-producing and background area of Hangjinqi area, we identified the indicator genera in the gas-producing fields of Xinzao and Shiguhao. Furthermore, the co-occurrence network analysis identifiedGemmatimonas,Solirubrobacter,Pseudonocardia,Brevibacillus,Aeromicrobium, andNocardioides as the key taxa in the gas-producing area, which were associated with the main functional modules of carbon and nitrogen cycling and organic matter degradation, contributing to the degradation of hydrocarbons in the surface soil of the gas-producing area.

[Objective] To study the variations of soil fungal diversity in the coal mine residue hills with vegetation restored for different years. [Methods] We selected the soil on the coal mine reside hills of Jiangcang Mine with different planting years (2, 4, and 6 years) as the research object, measured the soil chemical property and enzyme activity, and used high-throughput sequencing methods to measure the soil fungal diversity. [Results] As the duration of restoration increased, significant differences were observed in soil pH, total potassium, and organic matter. The activities of enzymes such as sucrase, urease, catalase, and phosphatase gradually increased, which enhanced the fungal richness and diversity in soil. The variations were more obvious after four years of restoration. The fungi were primarily dominated byAscomycota andBasidiomycota, with saprophytic fungi accounting for 43.2%–89.7%. Nitrogen content and soil enzyme activity were the key factors influencing fungal diversity in the grasslands of the coal mine area in Jiangcang. [Conclusion] Vegetation restoration can improve the chemical properties and fungal diversity in soil.

[Objective] Ectomycorrhizal fungi can shape the bacterial community in the ectomycorrhizosphere, which represents an important way to mobilize and acquire insoluble mineral elements from the soil. This study aims to investigate the composition and phosphate-solubilizing characteristics of the dominant phosphate-solubilizing bacteria (PSB) in the ectomycorrhizosphere ofCastanea henryi. [Methods] The transparent halo method was employed to isolate PSB from the ectomycorrhizosphere ofC.henryi. The strains were identified by 16S rRNA gene sequencing. The degradation abilities of the strains for tricalcium phosphate (TCP) and apatite were studied by liquid fermentation. A scanning electron microscope and a X-ray diffractometer were used to observe the appearance and crystal structures of the degradation products. [Results] Five highly efficient strains of PSB were isolated from the ectomycorrhizosphere ofC.henryi. Strains LSCh1, LSCh2, and LSCh5 were identified asBurkholderia lata, and strains LSCh3 and LSCh4 were identified asParaburkholderia sp. The degradation abilities of the strains for TCP followed the trend of LSCh3 (556.94 mg/L) > LSCh2 (206.91 mg/L) > LSCh1 (170.83 mg/L) > LSCh5 (55.16 mg/L) > LSCh4 (14.21 mg/L). The degradation abilities of the strains for apatite were in a descending order of LSCh2 (51.33 mg/L) > LSCh1 (43.51 mg/L) > LSCh3 (40.99 mg/L) > LSCh5 (1.11 mg/L) > LSCh4 (1.00 mg/L). [Conclusion] Strain LSCh3 showed good performance in degrading both TCP and apatite and induced the formation of carbonates. It is a plant growth-promoting bacterium with potential application values in improving the phosphorus nutrients of plants and the quality of soil.

Endophytic bacteria in the roots of a healthy plant not only form a symbiotic relationship with the host plant but also promote plant growth and enhance plant uptake of nutrients, being of importance for maintaining terrestrial ecological balance and improving the comprehensive management of karst rocky desertification. [Objective] To explore the endophytic bacterial communities in the roots of host plants and provide a theoretical basis for deeply understanding the interaction mechanisms between host plants and endophytic bacteria. [Methods] The community structures of endophytic bacteria and physicochemical properties of rhizosphere soil ofCerasus humilis (Bge.) Sok. introduced for the control of rocky desertification in the karst graben basin with different years were studied. [Results] Planting years ofC.humilis had a direct and significant influence on the rhizosphere soil quality and an indirect effect on the bacterial community in the roots. The endophytic bacterial community was mainly characterized by symbiotic interactions. The top three dominant bacterial genera identified by the co-occurrence network in the first year and third year wereStreptomyces,Burkholderia-Caballeronia-Paraburkholderia andChitinophaga, and the top three dominant bacterial genera in the fifth year wereStreptomyces,Chitinophaga and Haliangium, which had biocontrol effects. The endophytic bacterial community was shaped by stochastic ecological drift processes. [Conclusion] The differences of endophytic bacterial communities along the planting year gradient are due to the microbial diversity endowed by stochastic processes. The interactions among endophytic bacteria and the dominant bacteria with biocontrol effects could promote the colonization and growth ofC.humilis, thereby enhancing the ecological and economic benefits ofC.humilis for the comprehensive control of rocky desertification in the karst graben basin.

[Objective] To reveal the dynamic changes of soil microbial community and nutrient cycling process in the artificial grass squares dominated by pioneering plants such asLeymus secalinus andCarex praeclara in the alpine sandy land. [Methods] Metagenomic sequencing and qPCR were performed for the structure analysis, functional gene annotation, and absolute abundance determination of soil microbial communities, which were combined with soil physico-chemical factors for redundancy analysis. [Results] The artificial establishment of grass squares increased the total nitrogen by 20%–68%, available phosphorus by 10%–247%, and organic carbon by 19%–56% in sandy soils. Furthermore, it increased the bacterial and fungal abundance by 17%–81% and 2%–95%, respectively. Specifically, it increased the relative abundance of plant growth-promoting bacteria, such asSphingomonas,Bradyrhizobium,Nitrospira,Solirubrobacter, andNocardioides. Furthermore, the artificial establishment of grass squares enriched theamoCAB gene cluster and thenxrAB gene cluster associated with ammonia oxidation and nitrite oxidation in the nitrogen cycle. In addition, a genetic signature for complete ammonia oxidation was identified. [Conclusion] The artificial establishment of grass squares increases the content of soil nutrients and microbial abundance and promotes the nutrient cycling in alpine sandy areas. Moderate grazing can increase the diffusivity of nitrogen sinks and promote the colonization of native pioneer plants in the sandy ecosystem. The findings provide theoretical references for future restoration of sandy ecosystems in similar high-altitude areas.

[Objective] Studies have discovered that magnetite could be used as an extracellular electron transfer mediator to increase or decrease the microbial reduction rate of dyes. However, the mechanisms underlying these two distinct results remain to be elucidated. [Methods] In this study, magnetite was synthesized by the hydrothermal method and used for the anaerobic reduction of methyl orange (MO), a typical azo dye, byShewanella oneidensis MR-1. [Results] Magnetite exerted concentration-dependent effects on the degradation of MO. Specifically, low concentrations (20–50 mg/L) of magnetite increased the decolorization efficiency of MO by 4.07%–10.64%, while high concentrations (100–200 mg/L) of magnetite decreased the efficiency by 3.92%–18.35%, compared with the group with only bacteria for degradation. Furthermore, the changes in magnetite concentration affected cell surface morphology, metabolic activity, and electron transfer efficiency rather than the distribution of dyes on the microbial surface in the microbial reduction of MO. Low concentrations of magnetite increased ATP production by 1.08%–7.65% and led to the production of 0.033–0.051 mg/L Fe²⁺, while the high concentrations of magnetite decreased ATP production by 38.74%–60.14% and increased Fe²⁺ concentration to 0.091 mg/L. In addition, exogenous Fe²⁺ showed similar concentration-dependent effects on the anaerobic reduction of MO, i.e., promoting the MO reduction at low concentrations (0.01–0.02 mg/L) and inhibiting the reduction at high concentrations (> 0.05 mg/L). [Conclusion] Low concentrations of magnetite did not affect the bacterial cell morphology and improved the cell metabolic activity. A small amount of dissolved Fe²⁺ in the system favored the reduction of MO by bacteria, whereas high concentrations of magnetite showed an opposite influencing trend. This work enriches our understanding about the effect of magnetite on extracellular electron transfer and its application in the reductive transformation of organic pollutants.