微生物种间直接电子传递研究进展

一直以来氢气和甲酸被认为是微生物间电子传递的中间电子传递体.近年来的研究发现,微生物之间可以通过种间直接电子传递(DIET)来替代氢气/甲酸传递.DIET作为一种新发现的微生物间电子传递途径,其电子传递效率要高于传统的种间氢气/甲酸传递.DIET这一新发现改变了微生物互营生长代谢必须依赖氢气或甲酸等电子载体的传统认识,...     

微生物纳米导线的导电机制及功能

微生物种间直接电子传递是指在厌氧条件下,一种微生物将电子直接传递给另外一种微生物,将两种不同微生物的代谢途径耦合在一起,以达到互养共生的目的。细菌-古菌之间的直接电子传递是其物质转换与能量代谢的新途径和新调控机制,直接参与甲烷的合成以及与硫酸盐还原耦合的厌氧甲烷氧化,在驱动碳和硫的地球化学转化与循环中起着十分重要的作用。目前研究结果认为细菌-古菌之间的直接电子传递主要是由含多个血红素的C型细胞色素介导的,这些细胞色素能形成不间断的胞外电子传递途径,以电子多步跃迁机制在细菌和古菌的细胞质膜之间传递电子。     

微生物种间直接电子传递机理及应用研究进展

微生物胞内产生的电子转移到其他电子受体而获得能量的过程称为微生物胞外电子传递,其中,另一微生物作为电子受体时发生的电子传递称为微生物种间电子传递。根据微生物种间电子传递机制,可分间接种间电子传递和种间直接电子传递。由于种间直接电子传递不需要其他物质介导,因此较间接种间电子传递效率更高、能量利用更高。本文系统阐述了微生物进行胞外电子传递的机理及应用,重点分析了种间直接电子传递机理,并概述种间直接电子传递应用领域,为寻找更多电连接的微生物群落以及应用微生物提供参考。     

互营氧化产甲烷微生物种间电子传递研究进展

甲烷是重要的温室气体,也是典型的可再生性生物质能源。目前约70%的大气甲烷排放来源于产甲烷微生物过程。在产甲烷环境中,产甲烷菌与互营细菌形成互营关系,从而克服有机质厌氧分解反应的热力学能垒,实现短链脂肪酸和醇类物质的互营氧化产甲烷过程。该过程中,种间电子传递是关键步骤。本文首先概述了甲烷的研究意义及微生物互营降解有机质产甲烷的过程,然后分别综述了种间H2转移、种间甲酸转移和种间直接电子传递这3种种间电子传递机制的起源、发展、研究现状和未来所需要解决的研究问题。     

微生物种间电子传递的研究进展

种间电子传递可促进微生物发生共代谢,因而在地球生物化学循环和环境污染修复中具有重要意义。根据电子传递方式的不同可将种间电子传递分为直接种间电子传递（direct interspecies electron transfer,DIET）和间接种间电子传递（mediated interspecies electron transfer,MIET）,其中,直接种间电子传递由于易发生、效率高而受到更加广泛的关注。本文总结了近年来关于种间电子传递的研究进展,阐述了种间电子传递的途径,比较了DIET和MIET的优缺点,并对开发更多具有种间电子传递功能的微生物提出了建议,以期加深人们对于种间电子传递的理解,并对未来该领域的研究提供参考。     

产甲烷分离物中Clostridium spp.与Methanosarcina barkeri潜在的种间直接电子传递

【目的】革兰氏阴性菌Geobacter metallireducens可以与乙酸型产甲烷菌Methanosaeta harundinacea或Methanosarcina barkeri通过种间直接电子传递(DIET)还原CO2产甲烷。本实验室前期的研究发现Methanosarcina mazei和Geobacteraceae在铁还原富集培养中形成团聚体,可能存在直接电子传递。然而,革兰氏阳性菌(如Clostridium spp.)与产甲烷菌是否存在种间直接电子传递尚不明确。【方法】采用Hungate厌氧滚管法,以乙醇为唯一电子供体从铁还原富集培养体系中获得产甲烷分离物(S6)。通过T-RFLP及克隆文库分析群落多样性,结合循环伏安法等电化学方法研究产甲烷分离物的电活性。【结果】Clostridium spp.(与C.tunisiense相似性最高)和M.barkeri分别在S6细菌和古菌群落中占优势。S6与G.metallireducens共培养后铁还原和产甲烷能力未明显增加,Clostridium spp.可能与G.metallireducens类似,将电子直接传递给产甲烷菌M.barkeri产甲烷。此外,电化学检测发现,在用透析袋包裹电极阻碍微生物与电极表面通过直接接触形成生物膜的条件下,电流密度显著降低,并且循环伏安扫描无明显氧化还原峰。【结论】产甲烷分离物S6中存在直接电子传递途径。本工作提出在产甲烷分离物中占优势的革兰氏阳性菌Clostridium spp.和M.barkeri之间可能存在种间直接电子传递。     

导电碳颗粒促进污泥厌氧消化及微生物种间电子传递的研究进展

添加导电碳颗粒能够促进厌氧消化过程稳定性、底物降解率以及产沼气品质的同步提高。本文总结了以活性炭和生物炭为代表的导电碳颗粒对城市污泥厌氧消化的影响,探讨了导电碳颗粒促进城市污泥厌氧消化的机理,阐述了导电碳颗粒介导的微生物直接种间电子传递(Directinterspecies electrontransfer,DIET)在强化污泥厌氧消化中的作用机制,分析了复杂厌氧消化体系中微生物DIET互营关系的研究现状,同时对导电碳颗粒的物理化学特性及其对污泥厌氧消化产甲烷的影响进行了分析,最后对未来导电碳颗粒促进城市污泥厌氧消化的研究进行了展望。     

微生物互营产甲烷过程中的种间电子传递

甲烷作为全球第二大温室气体,是典型的可再生清洁能源,也是碳循环中的重要物质组成。大气中约74%的甲烷由产甲烷古菌和其他微生物的互营产生,种间电子传递(interspecies electron transfer, IET)是微生物菌群降低热力学能垒、实现互营产甲烷的核心过程。IET可分为间接种间电子传递(mediated interspecies electron transfer,MIET)和直接种间电子传递(direct interspecies electron transfer, DIET)两种类型,其中MIET依赖氢气、甲酸等载体完成电子的远距离传输,而DIET则依赖导电菌毛、细胞色素c等膜蛋白,通过微生物的直接接触实现电子传递。本文将从IET的研究历程出发,从电子传递机制、微生物种类、生态多样性等方面对微生物互营产甲烷过程中的两种IET类型进行比较,最后对未来待探索的方向进行展望。本综述有助于加深对微生物互营产甲烷过程中IET的理解,为解决由甲烷引发的全球气候变暖等生态问题提供理论支撑。     

厌氧甲烷氧化微生物物质代谢与能量代谢研究进展

甲烷既是一种温室气体,也是一种潜在的能源物质,其源与汇的平衡对地球化学循环及工程应用均有重要意义。厌氧甲烷氧化(anaerobic oxidation of methane,AOM)过程是深海、湿地和农田等自然生境中重要的甲烷汇,在缓解温室气体排放方面发挥了巨大作用。AOM微生物的中枢代谢机制及其能量转化途径则是介导厌氧甲烷氧化耦合其他物质还原的关键所在。因此,本文从电子受体多样性的视角,主要分析了硫酸盐型,硝酸盐/亚硝酸盐型,金属还原型厌氧甲烷氧化微生物的生理生化过程及环境分布,并对近些年发现的新型厌氧甲烷氧化进行了梳理;重点总结了厌氧甲烷氧化微生物细胞内电子传递路径以及胞外电子传递方式;根据厌氧甲烷氧化微生物环境分布及反应特征,就其生态学意义及在污染治理与能源回收方面的潜在应用价值进行了展望。本综述以期深化对厌氧甲烷氧化过程的微生物学认知,并为其潜在的工程应用方向提供新的思路。     

微生物铁呼吸机制研究进展

铁呼吸是厌氧环境中普遍存在的一种微生物代谢形式,多种古生菌和细菌都能进行铁呼吸.Fe(Ⅲ)的地球化学丰度比较高,为Fe(Ⅲ)还原菌提供了充足的电子受体,但自然中Fe(Ⅲ)多以不溶形式存在,使电子传递受阻.本文介绍了Fe(Ⅲ)还原菌的多样性,总结了4种铁呼吸机制:直接接触机制、螯合促溶机制、电子穿梭机制、纳米导线辅助机制,并对铁呼吸机制未来的研究方向进行了展望.     

Magnetite accelerates syntrophic acetate oxidation in methanogenic systems with high ammonia concentrations

Ammonia accumulation is a major inhibitory substance causing anaerobic digestion upset and failure in CH₄ production. At high ammonia levels, CH₄ production through syntrophic acetate oxidization (SAO) pathways is more tolerant to ammonia toxicity than the acetoclastic methanogenesis pathway, but the low CH₄ production rate through SAO constitutes the main reason for the low efficiency of energy recovery in anaerobic digesters treating ammonia‐rich substrates. In this study, we showed that acetate fermentation to CH₄ and CO₂ occurred through SAO pathway in the anaerobic reactors containing a high ammonia concentration (5.0 g l^?1 NH₄⁺–N), and the magnetite nanoparticles supplementation increased the CH₄ production rates from acetate by 36–58%, compared with the anaerobic reactors without magnetite under the same ammonia level. The mechanism of facilitated methanogenesis was proposed to be the establishment of direct interspecies electron transfer (DIET) for SAO, in which magnetite facilitated DIET between syntrophic acetate oxidizing bacteria and methanogens. High‐throughput 16S rRNA gene sequencing analysis revealed that the bacterial Geobacteraceae and the archaeal Methanosarcinaceae and Methanobacteriaceae might be involved in magnetite‐mediated DIET for SAO and CH₄ production. This study demonstrated that magnetite supplementation might provide an effective approach to accelerate CH₄ production rates in the anaerobic reactors treating wastewater containing high ammonia.     

陆地生态系统甲烷产生和氧化过程的微生物机理

陆地生态系统存在许多常年性或季节性缺氧环境,如:湿地、水稻土、湖泊沉积物、动物瘤胃、垃圾填埋场和厌氧生物反应器等。每年有大量有机物质进入这些环境,在缺氧条件下发生厌氧分解。甲烷是有机质厌氧分解的最终产物。产生的甲烷气体可通过缺氧-有氧界面释放到大气,产生温室效应,是重要的温室气体。产甲烷过程是缺氧环境中有机质分解的核心环节,而甲烷氧化是缺氧-有氧界面的重要微生物过程。甲烷的产生和氧化过程共同调控大气甲烷浓度,是全球碳循环不可分割的组成部分。对陆地生态系统甲烷产生和氧化过程的微生物机理研究进展进行了概要回顾和综述。主要内容包括:新型产甲烷古菌即第六和第七目产甲烷古菌和嗜冷嗜酸产甲烷古菌的发现;短链脂肪酸中间产物互营氧化过程与直接种间电子传递机制;新型甲烷氧化菌包括厌氧甲烷氧化菌和疣微菌属好氧甲烷氧化菌的发现;甲烷氧化菌生理生态与环境适应的新机制。这些研究进展显著拓展了人们对陆地生态系统甲烷产生和氧化机理的认识和理解。随着新一代土壤微生物研究技术的发展与应用,甲烷产生和氧化微生物研究领域将面临更多机遇和挑战,对未来发展趋势做了展望。     

Advances in direct interspecies electron transfer and conductive materials: Electron flux,organic degradation and microbial interaction

Direct interspecies electron transfer (DIET) via electrically conductive pili (e-pili) and c-type cytochrome between acetogens and methanogens has been proposed as an essential pathway for methane production. Supplements of conductive materials have been extensively found to promote methane production in microbial anaerobic treatment systems. This review comprehensively presents recent findings of DIET and the addition of conductive materials for methanogenesis and summarizes important results through aspects of electron flux, organic degradation, and microbial interaction. Conductive materials improve DIET and methanogenesis by acting as either substitute of e-pili or electron conduit between e-pili and electron acceptors. Other effects of conductive materials such as the change of redox potential may also be important factors for the stimulation. The type and organic loading rate of substrates affect the occurrence of DIET and stimulating effects of conductive materials. Geobacter, which can participate in DIET, were less enriched in anaerobic systems cultivated with non-ethanol substrates, suggesting the existence of other syntrophs with the capability of DIET. The coupling of communication systems such as quorum sensing may be a good strategy to achieve the formation of biofilm or granule enriched with syntrophic partners capable of DIET.     

Electron transfer of dissolved organic matter and its potential significance for anaerobic respiration in a northern bog

We investigated electron transfer processes of dissolved organic matter (DOM) and their potential importance for anaerobic heterotrophic respiration in a northern peatland. Electron accepting and donating capacities (EAC, EDC) of DOM were quantified using dissolved H₂S and ferric iron as reactants. Carbon turnover rates were obtained from porewater profiles (CO₂, CH₄) and inverse modeling. Carbon dioxide was released at rates of 0.2–5.9 mmol m⁻² day⁻¹ below the water table. Methane (CH₄) formation contributed <10%, and oxygen consumption 2% to 40%, leaving a major fraction of CO₂ production unexplained. DOM oxidized H₂S to thiosulfate and was reduced by dissolved ferric iron. Reduction with H₂S increased the subsequently determined EDC compared to untreated controls, indicating a reversibility of the electron transfer. In situ redox capacities of DOM ranged from 0.2 to 6.1 mEq g⁻¹ C (EAC) and from 0.0 to 1.4 mEq g⁻¹ C (EDC), respectively. EAC generally decreased with depth and changed after a water table drawdown and rebound by 20 and −45 mEq m⁻², respectively. The change in EAC during the water table fluctuation was similar to CH₄ formation rates. In peatlands, electron transfer of DOM may thus significantly contribute to the oxidation of reduced organic substrates by anaerobic heterotrophic respiration, or by maintaining the respiratory activity of sulfate reducers via provision of thiosulfate. Part of the anaerobic electron flow in peat soils is thus potentially diverted from methanogenesis, decreasing its contribution to the total carbon emitted to the atmosphere.     

纳米铁氧化物对Pelotomaculum schinkii培养系丙酸厌氧降解产甲烷的影响

微生物能利用导电材料进行电子传递,提高种间电子传递效率。铁基纳米导电物质可以加速土壤及厌氧消化系统中微生物间的种间电子传递,促进有机废弃物的产甲烷过程。前期获得了厌氧丙酸富集培养系,互营丙酸氧化菌（Pelotomaculum schinkii）在培养系中占优势,本研究考察了10~4 000 mg/L 纳米铁氧化物对丙酸降解产甲烷过程的作用及微生物的影响。结果表明,低浓度的铁基纳米材料对丙酸降解有一定的促进作用,而高浓度会抑制产甲烷：10~1 000 mg/L纳米Fe₃O₄对产甲烷无明显影响,1 500~4 000 mg/L最大产甲烷速率抑制了26%~80%,延滞期增加了174%~222%;10~200 mg/L纳米Fe₂O₃使最大产甲烷速率提高了21%~29%,1 500~4 000 mg/L最大产甲烷速率抑制了48%~58%,延滞期增加了29%~85%。微生物群落解析结果表明,与对照相比,10~1 000 mg/L纳米Fe₂O₃使P. schinkii相对丰度略有增加,而4 000 mg/L纳米₃O₄/Fe₂O₃使P. schinkii的相对丰度下降了70.7%和55.9%,说明高浓度纳米铁氧化物会抑制P. schinkii的活性,导致丙酸降解及产甲烷速率降低。     

Influence of Ni, Co, Fe, and Na additions on methane production in Sphagnum-dominated Northern American peatlands

Although Sphagnum (moss)-dominated, northern peatlandecosystems harbor methane (CH₄)-producing microorganisms(methanogens) and are a significant source of atmosphericCH₄, rates of CH₄ production vary widely amongdifferent systems. Very little work has been done to examine whetherconcentrations of cations and metal elements may account for thevariability. We examined rates of CH₄ production in peat fromfive geographically and functionally disparateSphagnum-dominated peatlands by incubating peat samples invitro with and without additions of trace metals (Fe, Ni, Co) andbase cations (Ca, Li, Na). In peat from the most mineral poor sites, theaddition of metals and Na enhanced CH₄ production beyond thatobserved in controls. The same treatments in mineral rich sites yieldedno effect or an inhibition of CH₄ production. None of thetreatments affected anaerobic respiration, measured as CO₂production, in the in vitro incubations of peat, except addedcitrate, suggesting that methanogens, and not the entire anaerobiccommunity, can be limited by the availability of metal elements andcations.     

Layered Structure of Bacterial and Archaeal Communities and Their In Situ Activities in Anaerobic Granules

The microbial community structure and spatial distribution of microorganisms and their in situ activities in anaerobic granules were investigated by 16S rRNA gene-based molecular techniques and microsensors for CH₄, H₂, pH, and the oxidation-reduction potential (ORP). The 16S rRNA gene-cloning analysis revealed that the clones related to the phyla Alphaproteobacteria (detection frequency, 51%), Firmicutes (20%), Chloroflexi (9%), and Betaproteobacteria (8%) dominated the bacterial clone library, and the predominant clones in the archaeal clone library were affiliated with Methanosaeta (73%). In situ hybridization with oligonucleotide probes at the phylum level revealed that these microorganisms were numerically abundant in the granule. A layered structure of microorganisms was found in the granule, where Chloroflexi and Betaproteobacteria were present in the outer shell of the granule, Firmicutes were found in the middle layer, and aceticlastic Archaea were restricted to the inner layer. Microsensor measurements for CH₄, H₂, pH, and ORP revealed that acid and H₂ production occurred in the upper part of the granule, below which H₂ consumption and CH₄ production were detected. Direct comparison of the in situ activity distribution with the spatial distribution of the microorganisms implied that Chloroflexi contributed to the degradation of complex organic compounds in the outermost layer, H₂ was produced mainly by Firmicutes in the middle layer, and Methanosaeta produced CH₄ in the inner layer. We determined the effective diffusion coefficient for H₂ in the anaerobic granules to be 2.66 × 10⁻⁵ cm² s⁻¹, which was 57% in water.     

Structural basis for electron and methyl-group transfer in a methyltransferase system operating in the reductive acetyl-CoA pathway

Several anaerobic acetogenic, methanogenic, hydrogenogenic, and sulfate-reducing microorganisms are able to use the reductive acetyl-CoA (Wood-Ljungdahl) pathway to convert CO₂ into biomass. The reductive acetyl-CoA pathway consists of two branches connected by the Co/Fe-containing corrinoid iron-sulfur protein (CoFeSP), which transfers a methyl group from a methyltransferase (MeTr)/methyltetrahydrofolate (CH₃-H₄ folate) complex to the reduced Ni-Ni-[4Fe-4S] cluster (cluster A) of acetyl-CoA synthase. We investigated the CoFeSP and MeTr couple of the hydrogenogenic bacterium Carboxydothermus hydrogenoformans and show that the two proteins are able to catalyze the methyl-group transfer reaction from CH₃-H₄ folate to the Co(I) center of CoFeSP. We determined the crystal structures of both proteins. The structure of CoFeSP includes the previously unresolved N-terminal domain of the large subunit of CoFeSP, revealing a unique four-helix-bundle-like architecture in which a [4Fe-4S] cluster is shielded by hydrophobic amino acids. It further reveals that the corrinoid and the [4Fe-4S] cluster binding domains are mobile, which is mandatory for the postulated electron transfer between them. Furthermore, we solved the crystal structures of apo-MeTr, CH₃-H₄-folate-bound MeTr, and H₄-folate-bound MeTr, revealing a substrate-induced closure of the CH₃-H₄ folate binding cavity of MeTr. We observed three different conformations of Asn200 depending on the substrate bound in the active site, demonstrating its conformational modulation by hydrogen-bonding interactions with the substrate. The observed flexibility could be essential to stabilize the transition state during methyl-group transfer. The conformational space and role of Asn200 are likely conserved in homologous cobalamin-dependent MeTrs such as methionine synthase.     

A pan‐Arctic synthesis of CH4 and CO2 production from anoxic soil incubations

Permafrost thaw can alter the soil environment through changes in soil moisture, frequently resulting in soil saturation, a shift to anaerobic decomposition, and changes in the plant community. These changes, along with thawing of previously frozen organic material, can alter the form and magnitude of greenhouse gas production from permafrost ecosystems. We synthesized existing methane (CH₄) and carbon dioxide (CO₂) production measurements from anaerobic incubations of boreal and tundra soils from the geographic permafrost region to evaluate large‐scale controls of anaerobic CO₂ and CH₄ production and compare the relative importance of landscape‐level factors (e.g., vegetation type and landscape position), soil properties (e.g., pH, depth, and soil type), and soil environmental conditions (e.g., temperature and relative water table position). We found fivefold higher maximum CH₄ production per gram soil carbon from organic soils than mineral soils. Maximum CH₄ production from soils in the active layer (ground that thaws and refreezes annually) was nearly four times that of permafrost per gram soil carbon, and CH₄ production per gram soil carbon was two times greater from sites without permafrost than sites with permafrost. Maximum CH₄ and median anaerobic CO₂ production decreased with depth, while CO₂:CH₄ production increased with depth. Maximum CH₄ production was highest in soils with herbaceous vegetation and soils that were either consistently or periodically inundated. This synthesis identifies the need to consider biome, landscape position, and vascular/moss vegetation types when modeling CH₄ production in permafrost ecosystems and suggests the need for longer‐term anaerobic incubations to fully capture CH₄ dynamics. Our results demonstrate that as climate warms in arctic and boreal regions, rates of anaerobic CO₂ and CH₄ production will increase, not only as a result of increased temperature, but also from shifts in vegetation and increased ground saturation that will accompany permafrost thaw.     

Interspecific hydrogen transfer during methanol degradation by Sporomusa acidovorans and hydrogenophilic anaerobes

In the presence of active hydrogenophilic sulfate-reducing bacteria, the homoacetogenic bacterium Sporomusa acidovorans did not produce acetate during methanol degradation. H₂S and presumably CO₂ were the only end products. Since the sulfate-reducer did not degrade methnol or acetate, the sulfidogenesis from methanol was related to a complete interspecific hydrogen transfer between both species.In coculture with hydrogenophilic methanogenic bacteria (Methanobacterium formicicum, Methanospirillum hungatei), the interspecific hydrogen transfer with S. acidovorans was incomplete. Beside CH₄ and presumably CO₂, acetate was produced. The results suggested that H₂-production and H₂-consumption were involved during anaerobic methanol degradation by S. acidovorans and the hydrogenophilic anaerobes play an important role during methanol degradation by homoacetogenic bacteria in anoxic environments.