A Ni-Fe-Cu center in a bifunctional carbon monoxide dehydrogenase/acetyl-CoA synthase

A metallocofactor containing iron, sulfur, copper, and nickel has been discovered in the enzyme carbon monoxide dehydrogenase/acetyl-CoA (coenzyme A) synthase from Moorella thermoacetica (f. Clostridium thermoaceticum). Our structure at 2.2 angstrom resolution reveals that the cofactor responsible for the assembly of acetyl-CoA contains a [Fe4S4] cubane bridged to a copper-nickel binuclear site. The presence of these three metals together in one cluster was unanticipated and suggests a newly discovered role for copper in biology. The different active sites of this bifunctional enzyme complex are connected via a channel, 138 angstroms long, that provides a conduit for carbon monoxide generated at the C-cluster on one subunit to be incorporated into acetyl-CoA at the A-cluster on the other subunit.     

A methylaspartate cycle in haloarchaea

Access to novel ecological niches often requires adaptation of metabolic pathways to cope with new environments. For conversion to cellular building blocks, many substrates enter central carbon metabolism via acetyl-coenzyme A (acetyl-CoA). Until now, only two such pathways have been identified: the glyoxylate cycle and the ethylmalonyl-CoA pathway. Prokaryotes in the haloarchaea use a third pathway by which acetyl-CoA is oxidized to glyoxylate via the key intermediate methylaspartate. Glyoxylate condensation with another acetyl-CoA molecule yields malate, the final assimilation product. This cycle combines reactions that originally belonged to different metabolic processes in different groups of prokaryotes, which suggests lateral gene transfer and evolutionary tinkering of acetate assimilation. Moreover, it requires elevated intracellular glutamate concentrations, as well as coupling carbon assimilation with nitrogen metabolism.     

Genetic evidence for transmembrane acetylation by lysosomes

Acetyl-CoA:alpha-glucosaminide N-acetyltransferase is a lysosomal-membrane enzyme deficient in a genetic disorder, Sanfilippo disease type C. The enzyme catalyzes the transfer of an acetyl group from cytoplasmic acetyl-coenzyme A (acetyl-CoA) to terminal alpha-glucosamine residues of heparan sulfate within the organelle. Previous kinetic experiments indicated that the enzyme carries out a transmembrane acetylation via a ping-pong mechanism; the reaction can therefore be dissected into two half reactions--acetylation of the enzyme, and transfer of the acetyl group to glucosamine. Cells derived from patients were found to differ in their ability to perform each half reaction. Five cell lines (derived from three families) were able to catalyze acetylation of the lysosomal membrane and to carry out acetyl-CoA/CoA exchange, whereas a sixth cell line was devoid of this activity.     

固碳微生物分子生态学研究

 减缓大气“温室效应”是目前最重要且亟待解决的环境问题之一。自养微生物具有极强的环境适应性和不容忽视的固碳潜力,研究微生物固定CO2的分子生态机理对于缓解全球气候变暖具有重要科学意义。目前发现的5条主要生物固碳途径中,卡尔文循环是自养生物固定CO2的主要途径,其中核酮糖-1,5-二磷酸羧化酶/加氧酶（RubisCO）是卡尔文循环中的关键酶,因此RubisCO及其编码基因被许多学者用于不同生态环境中固碳微生物群落结构和多样性的研究。以前的研究主要集中在水生生态系统,揭示了不同水生生态系统中固碳微生物的群落特点及其对不同生境的响应规律。近几年,随着陆地生态系统固碳微生物分子生态学研究的深入,国外学者发现土壤中存在大量的固碳自养微生物,它们在土壤中所起的具体作用和贡献有待进一步研究和验证。至今,国内针对土壤固碳微生物分子生态学的研究还未见报道。论文对固定CO2的微生物种类、固定机理以及近年来关于微生物固定CO2的分子生态学的研究进行了分析和总结,讨论了固碳微生物分子生态学研究存在的主要问题和今后的发展方向,旨在为中国固碳微生物分子生态学研究提供参考。     

耕作干扰下喀斯特土壤有机碳损失主要途径及其影响因素

西南喀斯特生态系统原生土壤有机碳(SOC)含量较高,但在开垦后急剧损失,然而目前对SOC损失过程、途径和机制仍缺乏充分认知。本研究基于不同频率翻耕处理(分别隔6、4、2、1个月翻耕一次,以免耕为对照)的原位控制试验,以土壤团聚体为切入点,通过对土壤CO_2排放和可溶性有机碳(DOC)淋失通量进行为期一年的连续监测,探讨了SOC损失的主要途径及其影响因素。结果发现:翻耕导致表层(0～10 cm)土壤SOC和5～8 mm粒级团聚体显著降低;一年后,各翻耕处理平均损失15.4%～27.6%的SOC,土壤DOC淋失量仅占SOC损失量的0.05%～0.10%,而土壤以CO_2形式释放的碳占SOC损失总量的22.7%～35.5%,是土壤碳损失的重要途径之一;SOC损失量与Ca~(2+)、Mg~(2+)淋失总量均呈显著正相关,说明在岩溶作用下以HCO_3-形式淋失是SOC损失的另一重要途径;土壤CO_2排放速率与5～8 mm粒级团聚体含量呈显著负相关,说明翻耕干扰导致5～8 mm团聚体崩解、受团聚体保护的闭蓄态SOC释放后迅速矿化是喀斯特SOC损失的主要机制。     

In situ stable isotope probing of methanogenic archaea in the rice rhizosphere

Microorganisms living in anoxic rice soils contribute 10 to 25% of global methane emissions. The most important carbon source for CH4 production is plant-derived carbon that enters soil as root exudates and debris. Pulse labeling of rice plants with 13CO2 resulted in incorporation of 13C into the ribosomal RNA of Rice Cluster I Archaea in the soil, indicating that this archaeal group plays a key role in CH4 production from plant-derived carbon. This group of microorganisms has not yet been isolated but appears to be of global environmental importance.     

Independent and parallel recruitment of preexisting mechanisms underlying C₄ photosynthesis

C? photosynthesis allows increased photosynthetic efficiency because carbon dioxide (CO?) is concentrated around the key enzyme RuBisCO. Leaves of C? plants exhibit modified biochemistry, cell biology, and leaf development, but despite this complexity, C? photosynthesis has evolved independently in at least 45 lineages of plants. We found that two independent lineages of C? plant, whose last common ancestor predates the divergence of monocotyledons and dicotyledons about 180 million years ago, show conserved mechanisms controlling the expression of genes important for release of CO(2) around RuBisCO in bundle sheath (BS) cells. Orthologous genes from monocotyledonous and dicotyledonous C? species also contained conserved regulatory elements that conferred BS specificity when placed into C? species. We conclude that these conserved functional genetic elements likely facilitated the repeated evolution of C? photosynthesis.     

2-甲基异茨醇降解菌阴沟肠杆菌Z5的分离鉴定及BAC文库的构建

从采集到的污水样品中分离得到1株高效降解2-甲基异茨醇(2-methylisoborneol,2-MIB)的菌株Z5,通过16S rDNA序列分析,鉴定为阴沟肠杆菌(Enterobactercloacae)。该菌在以2-MIB为唯一碳源的培养基中能正常生长代谢。经气相色谱-质谱分析,发现该菌对2-MIB的降解率高达89.7%。同时,测定了Z5在不同质量浓度2-MIB中的生长情况,结果表明:当2-MIB质量浓度为16μg/L时,其生长状况与在LB中最为接近。为了克隆降解2-MIB关键酶的编码基因并进一步研究其降解途径,本研究构建了E.cloacaeZ5的全基因组BAC文库,该文库覆盖了大约8倍的基因组,共计810个转化子,外源片段平均大小为40 kb。     

Atmospheric CO2: principal control knob governing Earth's temperature

Ample physical evidence shows that carbon dioxide (CO(2)) is the single most important climate-relevant greenhouse gas in Earth's atmosphere. This is because CO(2), like ozone, N(2)O, CH(4), and chlorofluorocarbons, does not condense and precipitate from the atmosphere at current climate temperatures, whereas water vapor can and does. Noncondensing greenhouse gases, which account for 25% of the total terrestrial greenhouse effect, thus serve to provide the stable temperature structure that sustains the current levels of atmospheric water vapor and clouds via feedback processes that account for the remaining 75% of the greenhouse effect. Without the radiative forcing supplied by CO(2) and the other noncondensing greenhouse gases, the terrestrial greenhouse would collapse, plunging the global climate into an icebound Earth state.     

The crystal structure of [Fe]-hydrogenase reveals the geometry of the active site

Biological formation and consumption of molecular hydrogen (H2) are catalyzed by hydrogenases, of which three phylogenetically unrelated types are known: [NiFe]-hydrogenases, [FeFe]-hydrogenases, and [Fe]-hydrogenase. We present a crystal structure of [Fe]-hydrogenase at 1.75 angstrom resolution, showing a mononuclear iron coordinated by the sulfur of cysteine 176, two carbon monoxide (CO) molecules, and the sp2-hybridized nitrogen of a 2-pyridinol compound with back-bonding properties similar to those of cyanide. The three-dimensional arrangement of the ligands is similar to that of thiolate, CO, and cyanide ligated to the low-spin iron in binuclear [NiFe]- and [FeFe]-hydrogenases, although the enzymes have evolved independently and the CO and cyanide ligands are not found in any other metalloenzyme. The related iron ligation pattern of hydrogenases exemplifies convergent evolution and presumably plays an essential role in H2 activation. This finding may stimulate the ongoing synthesis of catalysts that could substitute for platinum in applications such as fuel cells.     

Rising CO2 levels and the fecundity of forest trees

We determined the reproductive response of 19-year-old loblolly pine (Pinus taeda) to 4 years of carbon dioxide (CO2) enrichment (ambient concentration plus 200 microliters per liter) in an intact forest. After 3 years of CO2 fumigation, trees were twice as likely to be reproductively mature and produced three times as many cones and seeds as trees at ambient CO2 concentration. A disproportionate carbon allocation to reproduction under CO2 enrichment results in trees reaching maturity sooner and at a smaller size. This reproductive response to future increases in atmospheric CO2 concentration is expected to change loblolly dispersal and recruitment patterns.     

微藻气肥光生物反应器研究进展

利用微藻吸收工业废气中高浓度的CO2不仅可以显著增加微藻的生物量和油脂产量,还可以达到碳减排的目的,但是CO2在水体中溶解度较低一直是微藻利用高浓度CO2的瓶颈。探讨了CO2气肥耦联的微藻培养光生物反应器,着重阐述了两类气肥光生物反应器,即液体培养和半干固态培养光生物反应器,在CO2气源供应与利用上所做的改进和特点,详细比较了二者的装置特性、生物学特性、供气特点以及生产性能,为光自养微藻的高密度培养提供参考。     

溶解CO2对原料乳中主要腐败微生物生长参数的影响

研究了4℃下在原料乳中溶解CO2对其中主要腐败微生物生长参数的影响。试验以未处理的原料乳作对照组,CO2处理组的原料乳中CO2浓度分别为11.9、28.54、42.27 mmol.L-1。分别对各组中的假单胞菌、肠杆菌科细菌、乳酸菌和细菌总数的生长过程进行动态监测,并由此建立Gompertz数学模型、计算生长参数。结果表明,原料乳中溶解的CO2浓度越高,对3类主要腐败菌的抑制作用越大;CO2对革兰氏阴性菌的抑制作用大于革兰氏阳性菌;4℃下溶解42.27 mmol.L-1 CO2可以使原料乳的保质期延长1倍。     

Carbon flux and growth in mature deciduous forest trees exposed to elevated CO2

Whether rising atmospheric carbon dioxide (CO2) concentrations will cause forests to grow faster and store more carbon is an open question. Using free air CO2 release in combination with a canopy crane, we found an immediate and sustained enhancement of carbon flux through 35-meter-tall temperate forest trees when exposed to elevated CO2. However, there was no overall stimulation in stem growth and leaf litter production after 4 years. Photosynthetic capacity was not reduced, leaf chemistry changes were minor, and tree species differed in their responses. Although growing vigorously, these trees did not accrete more biomass carbon in stems in response to elevated CO2, thus challenging projections of growth responses derived from tests with smaller trees.     

Rainfall variability,carbon cycling,and plant species diversity in a mesic grassland

Ecosystem responses to increased variability in rainfall, a prediction of general circulation models, were assessed in native grassland by reducing storm frequency and increasing rainfall quantity per storm during a 4-year experiment. More extreme rainfall patterns, without concurrent changes in total rainfall quantity, increased temporal variability in soil moisture and plant species diversity. However, carbon cycling processes such as soil CO2 flux, CO2 uptake by the dominant grasses, and aboveground net primary productivity (ANPP) were reduced, and ANPP was more responsive to soil moisture variability than to mean soil water content. Our results show that projected increases in rainfall variability can rapidly alter key carbon cycling processes and plant community composition, independent of changes in total precipitation.     

Design of Nonionic Surfactants for Supercritical Carbon Dioxide

Interfacially active block copolymer amphiphiles have been synthesized and their self-assembly into micelles in supercritical carbon dioxide (CO2) has been demonstrated with small-angle neutron scattering (SANS). These materials establish the design criteria for molecularly engineered surfactants that can stabilize and disperse otherwise insoluble matter into a CO2 continuous phase. Polystyrene-b-poly(1,1-dihydroperfluorooctyl acrylate) copolymers self-assembled into polydisperse core-shell-type micelles as a result of the disparate solubility characteristics of the different block segments in CO2. These nonionic surfactants for CO2 were shown by SANS to be capable of emulsifying up to 20 percent by weight of a CO2-insoluble hydrocarbon into CO2. This result demonstrates the efficacy of surfactant-modified CO2 in reducing the large volumes of organic and halogenated solvent waste streams released into our environment by solvent-intensive manufacturing and process industries.     

A molecule carrier

We found that anthraquinone diffuses along a straight line across a flat, highly symmetric Cu111 surface. It can also reversibly attach one or two CO2 molecules as "cargo" and act as a "molecule carrier," thereby transforming the diffusive behavior of the CO2 molecules from isotropic to linear. Density functional theory calculations indicated a substrate-mediated attraction of approximately 0.12 electron volt (eV). Scanning tunneling microscopy revealed individual steps of the molecular complex on its diffusion pathway, with increases of approximately 0.03 and approximately 0.02 eV in the diffusion barrier upon attachment of the first and second CO2 molecule, respectively.     

Advances on the Responses of Root Dynamics to Increased Atmospheric CO2 and Global Climate Change

Plant roots dynamics responses to elevated atmospheric CO2 concentration, increased temperature and changed precipitation can be a key link between plant growth and long-term changes in soil organic matter and ecosystem carbon balance. This paper reviews some experiments and hypotheses developed in this area, which mainly include plant fine roots growth, root turnover, root respiration and other root dynamics responses to elevated CO2 and global climate change. Some recent new methods of studying root systems were also discussed and summarized. It holds herein that the assemblage of information about root turnover patterns, root respiration and other dynamic responses to elevated atmospheric CO2 and global climatic change can help to better understand and explore some new research areas. In this paper, some research challenges in the plant root responses to the elevated CO2 and other environmental factors during global climate change were also demonstrated.     

农田土壤温室气体排放研究进展(英文)

[目的]对农田土壤温室气体排放的研究进展进行综述。[方法]根据近几年国内外相关文献,对农田土壤中CO2、CH4和N2O的产生机理、排放特征及其主要影响因素进行归纳。[结果]土壤中温室气体CO2、CH4和N2O的产生和排放过程,是陆地生态系统碳氮循环的重要过程,是土壤碳氮库的重要输出途径,在全球碳氮循环中起到很重要作用,对其展开研究有利于减少其排放温室气体的量以及增大其吸收温室气体的能力,从而更有效地实现温室气体的减排。[结论]该研究有助于对温室气体排放规律和影响因素的正确了解,从而对温室气体减排以及研究气候变化提供理论依据。