A marine microbial consortium apparently mediating anaerobic oxidation of methane

A large fraction of globally produced methane is converted to CO2 by anaerobic oxidation in marine sediments. Strong geochemical evidence for net methane consumption in anoxic sediments is based on methane profiles, radiotracer experiments and stable carbon isotope data. But the elusive microorganisms mediating this reaction have not yet been isolated, and the pathway of anaerobic oxidation of methane is insufficiently understood. Recent data suggest that certain archaea reverse the process of methanogenesis by interaction with sulphate-reducing bacteria. Here we provide microscopic evidence for a structured consortium of archaea and sulphate-reducing bacteria, which we identified by fluorescence in situ hybridization using specific 16S rRNA-targeted oligonucleotide probes. In this example of a structured archaeal-bacterial symbiosis, the archaea grow in dense aggregates of about 100 cells and are surrounded by sulphate-reducing bacteria. These aggregates were abundant in gas-hydrate-rich sediments with extremely high rates of methane-based sulphate reduction, and apparently mediate anaerobic oxidation of methane.     

Iron corrosion by novel anaerobic microorganisms

Corrosion of iron presents a serious economic problem. Whereas aerobic corrosion is a chemical process, anaerobic corrosion is frequently linked to the activity of sulphate-reducing bacteria (SRB). SRB are supposed to act upon iron primarily by produced hydrogen sulphide as a corrosive agent and by consumption of 'cathodic hydrogen' formed on iron in contact with water. Among SRB, Desulfovibrio species--with their capacity to consume hydrogen effectively--are conventionally regarded as the main culprits of anaerobic corrosion; however, the underlying mechanisms are complex and insufficiently understood. Here we describe novel marine, corrosive types of SRB obtained via an isolation approach with metallic iron as the only electron donor. In particular, a Desulfobacterium-like isolate reduced sulphate with metallic iron much faster than conventional hydrogen-scavenging Desulfovibrio species, suggesting that the novel surface-attached cell type obtained electrons from metallic iron in a more direct manner than via free hydrogen. Similarly, a newly isolated Methanobacterium-like archaeon produced methane with iron faster than do known hydrogen-using methanogens, again suggesting a more direct access to electrons from iron than via hydrogen consumption.     

Chemolithoautotrophic metabolism of anaerobic extremely thermophilic archaebacteria

Several types of extremely thermophilic archaebacteria have recently been isolated from solfataric water holes, hot springs and hot sea floors. It has been shown that some of them can live using sulphur respiration of reduced carbon substrates as a source of energy, a type of metabolism previously described for the eubacterium Desulfuromonas. We report here that several extremely thermophilic archaebacteria can live with carbon dioxide as their sole carbon source, obtaining energy from the oxidation of hydrogen by sulphur, producing hydrogen sulphide. They are thus capable of a new type of anaerobic, purely chemolithoautotrophic metabolism, a possible primaeval mode of life.     

Anaerobic oxidation of short-chain hydrocarbons by marine sulphate-reducing bacteria

The short-chain hydrocarbons ethane, propane and butane are constituents of natural gas. They are usually assumed to be of thermochemical origin, but biological formation of ethane and propane has been also observed. Microbial utilization of short-chain hydrocarbons has been shown in some aerobic species but not in anaerobic species of bacteria. On the other hand, anaerobic utilization of short-chain hydrocarbons would in principle be expected because various anaerobic bacteria grow with higher homologues (> or =C(6)). Indeed, chemical analyses of hydrocarbon-rich habitats with limited or no access of oxygen indicated in situ biodegradation of short-chain hydrocarbons. Here we report the enrichment of sulphate-reducing bacteria (SRB) with such capacity from marine hydrocarbon seep areas. Propane or n-butane as the sole growth substrate led to sediment-free sulphate-reducing enrichment cultures growing at 12, 28 or 60 degrees C. With ethane, a slower enrichment with residual sediment was obtained at 12 degrees C. Isolation experiments resulted in a mesophilic pure culture (strain BuS5) that used only propane and n-butane (methane, isobutane, alcohols or carboxylic acids did not support growth). Complete hydrocarbon oxidation to CO2 and the preferential oxidation of 12C-enriched alkanes were observed with strain BuS5 and other cultures. Metabolites of propane included iso- and n-propylsuccinate, indicating a subterminal as well as an unprecedented terminal alkane activation with involvement of fumarate. According to 16S ribosomal RNA analyses, strain BuS5 affiliates with Desulfosarcina/Desulfococcus, a cluster of widespread marine SRB. An enrichment culture with propane growing at 60 degrees C was dominated by Desulfotomaculum-like SRB. Our results suggest that diverse SRB are able to thrive in seep areas and gas reservoirs on propane and butane, thus altering the gas composition and contributing to sulphide production.     

SAR11 marine bacteria require exogenous reduced sulphur for growth

Sulphur is a universally required cell nutrient found in two amino acids and other small organic molecules. All aerobic marine bacteria are known to use assimilatory sulphate reduction to supply sulphur for biosynthesis, although many can assimilate sulphur from organic compounds that contain reduced sulphur atoms. An analysis of three complete 'Candidatus Pelagibacter ubique' genomes, and public ocean metagenomic data sets, suggested that members of the ubiquitous and abundant SAR11 alphaproteobacterial clade are deficient in assimilatory sulphate reduction genes. Here we show that SAR11 requires exogenous sources of reduced sulphur, such as methionine or 3-dimethylsulphoniopropionate (DMSP) for growth. Titrations of the algal osmolyte DMSP in seawater medium containing all other macronutrients in excess showed that 1.5 x 10(8) SAR11 cells are produced per nanomole of DMSP. Although it has been shown that other marine alphaproteobacteria use sulphur from DMSP in preference to sulphate, our results indicate that 'Cand. P. ubique' relies exclusively on reduced sulphur compounds that originate from other plankton.     

Evidence of giant sulphur bacteria in Neoproterozoic phosphorites

In situ phosphatization and reductive cell division have recently been discovered within the vacuolate sulphur-oxidizing bacteria. Here we show that certain Neoproterozoic Doushantuo Formation (about 600 million years bp) microfossils, including structures previously interpreted as the oldest known metazoan eggs and embryos, can be interpreted as giant vacuolate sulphur bacteria. Sulphur bacteria of the genus Thiomargarita have sizes and morphologies similar to those of many Doushantuo microfossils, including symmetrical cell clusters that result from multiple stages of reductive division in three planes. We also propose that Doushantuo phosphorite precipitation was mediated by these bacteria, as shown in modern Thiomargarita-associated phosphogenic sites, thus providing the taphonomic conditions that preserved other fossils known from the Doushantuo Formation.     

Effect of evaporite deposition on Early Cretaceous carbon and sulphur cycling

The global carbon and sulphur cycles are central to our understanding of the Earth's history, because changes in the partitioning between the reduced and oxidized reservoirs of these elements are the primary control on atmospheric oxygen concentrations. In modern marine sediments, the burial rates of reduced carbon and sulphur are positively coupled, but high-resolution isotope records indicate that these rates were inversely related during the Early Cretaceous period. This inverse relationship is difficult to reconcile with our understanding of the processes that control organic matter remineralization and pyrite burial. Here we show that the inverse correlation can be explained by the deposition of evaporites during the opening of the South Atlantic Ocean basin. Evaporite deposition can alter the chemical composition of sea water, which can in turn affect the ability of sulphate-reducing bacteria to remineralize organic matter and mediate pyrite burial. We use a reaction-transport model to quantify these effects, and the resulting changes in the burial rates of carbon and sulphur, during the Early Cretaceous period. Our results indicate that deposition of the South Atlantic evaporites removed enough sulphate from the ocean temporarily to reduce biologically mediated pyrite burial and organic matter remineralization by up to fifty per cent, thus explaining the inverse relationship between the burial rates of reduced carbon and sulphur during this interval. Furthermore, our findings suggest that the effect of changing seawater sulphate concentrations on the marine subsurface biosphere may be the key to understanding other large-scale perturbations of the global carbon and sulphur cycles.     

Endosymbiotic sulphate-reducing and sulphide-oxidizing bacteria in an oligochaete worm

Stable associations of more than one species of symbiont within a single host cell or tissue are assumed to be rare in metazoans because competition for space and resources between symbionts can be detrimental to the host. In animals with multiple endosymbionts, such as mussels from deep-sea hydrothermal vents and reef-building corals, the costs of competition between the symbionts are outweighed by the ecological and physiological flexibility gained by the hosts. A further option for the coexistence of multiple symbionts within a host is if these benefit directly from one another, but such symbioses have not been previously described. Here we show that in the gutless marine oligochaete Olavius algarvensis, endosymbiotic sulphate-reducing bacteria produce sulphide that can serve as an energy source for sulphide-oxidizing symbionts of the host. Thus, these symbionts do not compete for resources but rather share a mutalistic relationship with each other in an endosymbiotic sulphur cycle, in addition to their symbiotic relationship with the oligochaete host.     

Early oxygenation of the terrestrial environment during the Mesoproterozoic

Geochemical data from ancient sedimentary successions provide evidence for the progressive evolution of Earth's atmosphere and oceans. Key stages in increasing oxygenation are postulated for the Palaeoproterozoic era (～2.3?billion years ago, Gyr ago) and the late Proterozoic eon (about 0.8?Gyr ago), with the latter implicated in the subsequent metazoan evolutionary expansion. In support of this rise in oxygen concentrations, a large database shows a marked change in the bacterially mediated fractionation of seawater sulphate to sulphide of Δ(34)S?相似文献   

复合型生物絮凝剂产生菌发酵动力学研究(英文)

为了优化复合型生物絮凝剂生产的发酵过程,对絮凝剂产生菌F2-F6发酵生产复合型生物絮凝剂的动力学进行了研究,利用数学建模方法得到了描述F2-F6菌体生长,絮凝剂合成及底物消耗动力学方程和动力学参数.实验和方程数据的比较结果证明动力学方程计算值与实验值拟合良好,为复合型生物絮凝剂的放大工业化生产提供依据.     

Evolution of a new enzyme for carbon disulphide conversion by an acidothermophilic archaeon

Extremophilic organisms require specialized enzymes for their exotic metabolisms. Acid-loving thermophilic Archaea that live in the mudpots of volcanic solfataras obtain their energy from reduced sulphur compounds such as hydrogen sulphide (H(2)S) and carbon disulphide (CS(2)). The oxidation of these compounds into sulphuric acid creates the extremely acidic environment that characterizes solfataras. The hyperthermophilic Acidianus strain A1-3, which was isolated from the fumarolic, ancient sauna building at the Solfatara volcano (Naples, Italy), was shown to rapidly convert CS(2) into H(2)S and carbon dioxide (CO(2)), but nothing has been known about the modes of action and the evolution of the enzyme(s) involved. Here we describe the structure, the proposed mechanism and evolution of a CS(2) hydrolase from Acidianus A1-3. The enzyme monomer displays a typical β-carbonic anhydrase fold and active site, yet CO(2) is not one of its substrates. Owing to large carboxy- and amino-terminal arms, an unusual hexadecameric catenane oligomer has evolved. This structure results in the blocking of the entrance to the active site that is found in canonical β-carbonic anhydrases and the formation of a single 15-?-long, highly hydrophobic tunnel that functions as a specificity filter. The tunnel determines the enzyme's substrate specificity for CS(2), which is hydrophobic. The transposon sequences that surround the gene encoding this CS(2) hydrolase point to horizontal gene transfer as a mechanism for its acquisition during evolution. Our results show how the ancient β-carbonic anhydrase, which is central to global carbon metabolism, was transformed by divergent evolution into a crucial enzyme in CS(2) metabolism.     

Systematic design of chemical oscillators using complexation and precipitation equilibria

Concentration oscillations are ubiquitous in living systems, where they involve a wide range of chemical species. In contrast, early in vitro chemical oscillators were all derived from two accidentally discovered reactions based on oxyhalogen chemistry. Over the past 25 years, the use of a systematic design algorithm, in which a slow feedback reaction periodically drives a bistable system in a flow reactor between its two steady states, has increased the list of oscillating chemical reactions to dozens of systems. But these oscillating reactions are still confined to a handful of elements that possess multiple stable oxidation states: halogens, sulphur and some transition metals. Here we show that linking a 'core' oscillator to a complexation or precipitation equilibrium can induce concentration oscillations in a species participating in the equilibrium. We use this method to design systems that produce periodic pulses of calcium, aluminium or fluoride ions. The ability to generate oscillations in elements possessing only a single stable oxidation state (for example, Na+, F-, Ca2+) may lead to reactions that are useful for coupling to or probing living systems, or that help us to understand new mechanisms by which periodic behaviour may arise.     

Proton translocation by cytochrome c oxidase.

Cell respiration in mitochondria and some bacteria is catalysed by cytochrome c oxidase, which reduces O2 to water, coupled with translocation of four protons across the mitochondrial or bacterial membrane. The enzyme's catalytic cycle consists of a reductive phase, in which the oxidized enzyme receives electrons from cytochrome c, and an oxidative phase, in which the reduced enzyme is oxidized by O2. Previous studies indicated that proton translocation is coupled energetically only to the oxidative phase, but this has been challenged. Here, with the purified enzyme inlaid in liposomes, we report time-resolved measurements of membrane potential, which show that half of the electrical charges due to proton-pumping actually cross the membrane during reduction after a preceding oxidative phase. pH measurements confirm that proton translocation also occurs during reduction, but only when immediately preceded by an oxidative phase. We conclude that all the energy for proton translocation is conserved in the enzyme during its oxidation by O2. One half of it is utilized for proton-pumping during oxidation, but the other half is unlatched for this purpose only during re-reduction of the enzyme.     

专性厌氧菌发酵罐制氢工艺

采用批式发酵工艺研究了专性厌氧菌P的产氢特性.分别探讨了P菌在小样及发酵罐扩大试验中的生长周期、pH值、葡萄糖浓度以及糖蜜浓度等生态因子对产氢能力的影响.结果表明,P菌是一种高效产氢的菌株,在培养10h后进入对数生长期和高速产氢阶段.当葡萄糖浓度为10 g/L,初始pH为7.0,接种比例为10％时,小样发酵和发酵罐的气体总产量均达到最大值,分别为485 mL和17.4L;在发酵罐中,通过连续补加NaOH溶液使pH恒定在7.0左右,可使每升培养基产氢量达到2.473 L,比小样提高了5％,此时葡萄糖分解率达到95.2％,且氢气的质量分数达到68.73％;利用糖蜜作为发酵底物,具有广阔的经济效益和除废产能的环境效益,当糖蜜底物浓度为35 g/L时的产气能力最佳,发酵罐中最大产气量为22 L.     

一种产氢产乙酸菌互营共培养体的筛选及其群落结构解析

厌氧消化系统中的产氢产乙酸菌在营养生态位上位于产酸发酵菌群和产甲烷菌群之间,在功能上起着承上启下的重要作用.该菌群具有与耗氢菌互营共生的特性,其分离纯化非常困难.为了深入了解其生理生态特性,为开发高效的厌氧生物处理技术提供理论基础,采用丙酸和丁酸混合培养基,以具有甲烷发酵功能的厌氧活性污泥为出发菌群,进行了产氢产乙酸菌互营共培养体的选育,并借助于PCR-DGGE技术对其菌群结构进行了解析.经过选择培养基的不断传代培养,最终筛选到2个产氢产乙酸互营共培养体7-m-2a和11-O-1.这2个共培养体不仅对丙酸和丁酸具有很强的降解和产乙酸能力,而且不产甲烷和硫化氢.在这种非产甲烷菌和非硫酸盐还原菌与产氢产乙酸菌组成的互营共培养体中.含有专性的互营产乙酸菌Desulfotomaculum sp.Iso-W2及其伴生菌,其中的伴生菌是能利用甲酸盐和H2/CO2的Uncultured bacterium 054E12_B_DI_P58和Sedimentibacter sp.JN18_A14_H.对这一新的产氢产乙酸菌互营共培养体的发现和选育成功,为更全面地研究产氢产乙酸菌的生理生态特性提供了样本.     

Hydrogen is an energy source for hydrothermal vent symbioses

The discovery of deep-sea hydrothermal vents in 1977 revolutionized our understanding of the energy sources that fuel primary productivity on Earth. Hydrothermal vent ecosystems are dominated by animals that live in symbiosis with chemosynthetic bacteria. So far, only two energy sources have been shown to power chemosynthetic symbioses: reduced sulphur compounds and methane. Using metagenome sequencing, single-gene fluorescence in situ hybridization, immunohistochemistry, shipboard incubations and in situ mass spectrometry, we show here that the symbionts of the hydrothermal vent mussel Bathymodiolus from the Mid-Atlantic Ridge use hydrogen to power primary production. In addition, we show that the symbionts of Bathymodiolus mussels from Pacific vents have hupL, the key gene for hydrogen oxidation. Furthermore, the symbionts of other vent animals such as the tubeworm Riftia pachyptila and the shrimp Rimicaris exoculata also have hupL. We propose that the ability to use hydrogen as an energy source is widespread in hydrothermal vent symbioses, particularly at sites where hydrogen is abundant.     

柠檬酸强化黄铜尾矿的生物浸矿

通过摇瓶试验研究混合硫杆菌浸出黄铜矿尾矿砂,并初步探讨不同矿浆质量浓度和柠檬酸质量浓度对浸提实验的影响。研究结果表明,添加柠檬酸在一定质量浓度范围内对黄铜矿尾矿砂的硫杆菌浸提有促进作用。在整个浸提实验中,浸矿效率最高达到44.8%,溶液中柠檬酸质量浓度和矿浆质量浓度都会直接影响细菌的氧化活性和浸矿效果。     

Deterioration of the seventeenth-century warship Vasa by internal formation of sulphuric acid

The seventeenth-century Swedish warship, Vasa, was recovered in good condition after 333 years in the cold brackish water of Stockholm harbour. After extensive treatment to stabilize and dry the ship's timbers, the ship has been on display in the Vasa Museum since 1990. However, high acidity and a rapid spread of sulphate salts were recently observed on many wooden surfaces, which threaten the continued preservation of the Vasa. Here we show that, in addition to concentrations of sulphate mostly on the surface of oak beams, elemental sulphur has accumulated within the beams (0.2-4 per cent by mass), and also sulphur compounds of intermediate oxidation states exist. The overall quantity of elemental sulphur could produce up to 5,000 kg of sulphuric acid when fully oxidized. We suggest that the oxidation of the reduced sulphur--which probably originated from the penetration of hydrogen sulphide into the timbers as they were exposed to the anoxic water--is being catalysed by iron species released from the completely corroded original iron bolts, as well as from those inserted after salvage. Treatments to arrest acid wood hydrolysis of the Vasa and other wooden marine-archaeological artefacts should therefore focus on the removal of sulphur and iron compounds.     

热处理对餐厨垃圾厌氧发酵产氢的影响

餐厨垃圾中有机物含量高,以沼渣为产氢菌种来源,利用餐厨垃圾为原料研究厌氧发酵制备氢气,研究通过热处理沼渣对餐厨垃圾厌氧发酵产氢的影响。结果表明,餐厨垃圾是理想的厌氧发酵产氢底物,热处理能够有效的抑制耗氢微生物的活性,提高产氢气浓度。未加热处理发酵产气量大,氢气最大浓度为29%;100℃加热处理15 min发酵产氢气最大浓度为38%,产气量大;100℃加热处理30 min发酵产氢气最大浓度为35%,产气量下降。以餐厨垃圾为发酵底物微生物产氢发酵的最佳p H值为5.0~6.0。     

活性污泥制氢系统中发酵细菌的分离与鉴定

分离鉴定高效产氢发酵细菌是发酵发生物制氢技术的重要前提,利用Hungater技术与宽体窄颈培养瓶平板技术,以及LM-1和HPB-LR培养基分离鉴定厌氧发酵产氢细菌获得六株产氢细菌,葡萄糖是他们最适宜的底物.他们的产氢代谢为乙醇发酵型.产氢细菌发酵液相末端产物分析表明乙醇和乙酸占其总代谢产物的95?%.生理生化和形态学特征分析表明它们属于一种特殊的微生物类群.16SrDNA碱基序列分析表明它们可以划分为新的种属.