不同pH水平下两种菌根真菌对紫云英生长的影响及其相互作用

设计在不同pH水平（4.3、5.1、5.8、6.8）下两种VA菌根真菌Glomus mosseae和Gigaspora margarita对紫云英Astragalus sinicus进行单接种、混合接种及无接种对照的盆栽实验。对紫云英地上和地下部分生物量、根部侵染率、SDH和ALP酶活进行了检测。实验结果表明：紫云英的生长效应与VA菌根真菌的侵染率及两种酶活成明显相关性。土壤pH升高,单接种Glomus mosseae和混合接种的侵染率也随之升高,而单接种Gigaspora margarita的侵染率呈现     

Improving joint torque calculations: optimization-based inverse dynamics to reduce the effect of motion errors

The accuracy of joint torques calculated from inverse dynamics methods is strongly dependent upon errors in body segment motion profiles, which arise from two sources of noise: the motion capture system and movement artifacts of skin-mounted markers. The current study presents a method to increase the accuracy of estimated joint torques through the optimization of the angular position data used to describe these segment motions. To compute these angular data, we formulated a constrained nonlinear optimization problem with a cost function that minimizes the difference between the known ground reaction forces (GRFs) and the GRF calculated via a top-down inverse dynamics solution. To evaluate this approach, we constructed idealized error-free reference movements (of squatting and lifting) that produced a set of known “true” motions and associated true joint torques and GRF. To simulate real-world inaccuracies in motion data, these true motions were perturbed by artificial noise. We then applied our approach to these noise-induced data to determine optimized motions and related joint torques. To evaluate the efficacy of the optimization approach compared to traditional (bottom-up or top-down) inverse dynamics approaches, we computed the root mean square error (RMSE) values of joint torques derived from each approach relative to the expected true joint torques. Compared to traditional approaches, the optimization approach reduced the RMSE by 54% to 79%. Average reduction due to our method was 65%; previous methods only achieved an overall reduction of 30%. These results suggest that significant improvement in the accuracy of joint torque calculations can be achieved using this approach.     

Characterization of the Escherichia coli CcmH protein reveals new insights into the redox pathway required for cytochrome c maturation

The CcmH protein of Escherichia coli is encoded by the last gene of the ccm gene cluster required for cytochrome c maturation. A mutant in which the entire ccmH gene was deleted failed to synthesize both indigenous and foreign c-type cytochromes. However, deletion of the C-terminal hydrophilic domain homologous to CycH of other gram-negative bacteria affected neither the biogenesis of indigenous c-type cytochromes nor that of the Bradyrhizobium japonicum cytochrome c ₅₅₀. This confirmed that only the N-terminal domain containing a conserved CXXC motif is required in E. coli. PhoA fusion analysis showed that this domain is periplasmic. Site-directed mutagenesis of the cysteines of the CXXC motif revealed that both cysteines are required for cytochrome c maturation during aerobic growth, whereas only the second cysteine is required for cytochrome c maturation during anaerobic growth. The deficiency of the point mutants was complemented when 2-mercapto-ethanesulfonic acid was added to growing cells; other thiol compounds did not stimulate cytochrome c formation in these strains. We propose a model for the reaction sequence in which CcmH keeps the heme binding site of apocytochrome c in a reduced form for subsequent heme ligation. Received: 7 September 1998 / Accepted: 15 November 1998     

Ability of the endangered species Papaver fauriei to produce hybrids with a cultivated poppy (Papaver sp.)

Papaver fauriei is an endemic and endangered species that grows only on the gravelly alpine slopes of Mt. Rishiri, Japan. Cultivated poppy (Papaver sp.), the species name of which is unknown, has been introduced to the natural habitats of P. fauriei through human activities. Because the appearance and internal transcribed spacer (ITS) sequences of these two poppies are highly similar, it is of concern that they could produce hybrids in their natural habitats. Thus, first, the ability of these two poppies to produce hybrids was analyzed by artificial fertilization in this study. A large number of seeds were produced by reciprocal crosses between P. fauriei and the cultivated poppy, comparable with the number of seeds obtained by self‐ or cross‐fertilization of P. fauriei or the cultivated poppy. In addition, high germination was observed for seeds obtained from crosses between the two poppies, and deleterious phenotypes, such as albinism and dwarfism, were not detected in the F₁ generation. These results indicate that after pollination, there is no reproductive isolation between the two poppies. Second, we sequenced the internal transcribed spacer (ITS) region of 240 poppy individuals collected from the gravelly alpine slopes of Mt. Rishiri, and 66 showed the sequence of P. fauriei, whereas 174 showed the sequence of the cultivated poppy. However, the ITS sequence that confirms hybridism between the two poppies was not detected in these individuals, indicating that hybridization of P. fauriei and the cultivated poppy rarely occurs under natural conditions. Unknown mechanism(s) appear to prevent cross‐pollination between the two poppies.     

Phenotypic noise and the cost of complexity

Experimental studies demonstrate the existence of phenotypic diversity despite constant genotype and environment. Theoretical models based on a single phenotypic character predict that during an adaptation event, phenotypic noise should be positively selected far from the fitness optimum because it increases the fitness of the genotype, and then be selected against when the population reaches the optimum. It is suggested that because of this fitness gain, phenotypic noise should promote adaptive evolution. However, it is unclear how the selective advantage of phenotypic noise is linked to the rate of evolution, and whether any advantage would hold for more realistic, multidimensional phenotypes. Indeed, complex organisms suffer a cost of complexity, where beneficial mutations become rarer as the number of phenotypic characters increases. Using a quantitative genetics approach, we first show that for a one-dimensional phenotype, phenotypic noise promotes adaptive evolution on plateaus of positive fitness, independently from the direct selective advantage on fitness. Second, we show that for multidimensional phenotypes, phenotypic noise evolves to a low-dimensional configuration, with elevated noise in the direction of the fitness optimum. Such a dimensionality reduction of the phenotypic noise promotes adaptive evolution and numerical simulations show that it reduces the cost of complexity.     

A Water‐Soluble Cu Complex as Molecular Catalyst for Electrocatalytic CO2 Reduction on Graphene‐Based Electrodes

A structurally simple molecular 1,10‐phenanthroline‐Cu complex on a mesostructured graphene matrix that can be active and selective toward CO₂ reduction over H₂ evolution in an aqueous solution is reported. The active sites consist of Cu(I) center in a distorted trigonal bipyramidal geometry, which enables the adsorption of CO₂ with η¹‐COO‐like configuration to commence the catalysis, with a turnover frequency of ≈45 s^?1 at ?1 V versus reversible hydrogen electrode. Using in situ infrared spectroelectrochemical investigation, it is demonstrated that the Cu complex can be reversibly heterogenized near the graphene surface via potential control. An increase of electron density in the complex is observed as a result of the interaction from the electric field, which further tunes the electron distribution in the neighboring CO₂. It is also found that the mesostructure of graphene matrix favored CO₂ reduction on the Cu center over hydrogen evolution by limiting mass transport from the bulk solution to the electrode surface.     

A novel twist on molecular interactions between thioredoxin and nicotinamide adenine dinucleotide phosphate‐dependent thioredoxin reductase

The ubiquitous disulfide reductase thioredoxin (Trx) regulates several important biological processes such as seed germination in plants. Oxidized cytosolic Trx is regenerated by nicotinamide adenine dinucleotide phosphate (NADPH)‐dependent thioredoxin reductase (NTR) in a multistep transfer of reducing equivalents from NADPH to Trx via a tightly NTR‐bound flavin. Here, interactions between NTR and Trx are predicted by molecular modelling of the barley NTR:Trx complex (HvNTR2:HvTrxh2) and probed by site directed mutagenesis. Enzyme kinetics analysis reveals mutants in a loop of the flavin adenine dinucleotide (FAD)‐binding domain of HvNTR2 to strongly affect the interaction with Trx. In particular, Trp42 and Met43 play key roles for recognition of the endogenous HvTrxh2. Trx from Arabidopsis thaliana is also efficiently recycled by HvNTR2 but turnover in this case appears to be less dependent on these two residues, suggesting a distinct mode for NTR:Trx recognition. Comparison between the HvNTR2:HvTrxh2 model and the crystal structure of the Escherichia coli NTR:Trx complex reveals major differences in interactions involving the FAD‐ and NADPH‐binding domains as supported by our experiments. Overall, the findings suggest that NTR:Trx interactions in different biological systems are fine‐tuned by multiple intermolecular contacts. Proteins 2014; 82:607–619. © 2013 Wiley Periodicals, Inc.     

油藏嗜热菌与膨润土的相互作用及其对储层防膨的意义

[目的]本文从胜利油田沾3区块的高温油藏的原油采出液中分离得到一株嗜热菌,通过其与膨润土的相互作用,尝试探讨油藏微生物作为油藏储层中水敏性矿物（如蒙皂石）改性剂的可能性。[意义]研究结果将在降低水敏矿物的膨胀性能,为解决水驱采油中遇到的水敏效应的瓶颈问题提供微生物的新途径。[结果]所得菌株为革兰氏阳性菌,呈杆状,具芽孢,兼性厌氧,鉴定为Geobacillus icigianus SL-1。菌株SL-1在厌氧条件下能够还原蒙皂石的结构铁。扫描电镜（SEM）结果显示,无菌对照体系中,蒙皂石呈不规则薄片状。而经微生物作用后,除薄片状蒙皂石外,另有板状次生矿物的生成。进一步能谱（EDS）分析表明,与薄片状蒙皂石相比,板状矿物含有较高的Al/Si比值,且含有明显的K⁺信号。XRD结果显示,经过微生物作用后,固相物质中蒙皂石的百分比下降至47.7%,伊利石百分比上升至29.1%,而无菌对照组中蒙皂石的百分含量则为70.4%,伊利石的百分比则为19.8%。XRD物相分析和EDS结果均证实经过微生物作用后,部分蒙皂石转化成了伊利石。膨胀性能的分析进一步揭示菌株SL-1作用后,矿物膨胀性较初始矿物显著降低,缩膨率达到25.9%。以上结果为油藏储层防膨提供了重要的实验依据。     

Electrochemical checking of aerobic isolates from electrochemically active biofilms formed in compost

Aims:  To design a cyclic voltammetry (CV) procedure to check the electrochemical activity of bacterial isolates that may explain the electrochemical properties of biofilms formed in compost.
Methods and Results:  Bacteria catalysing acetate oxidation in garden compost were able to form electrochemically active biofilms by transferring electrons to an electrode under chronoamperometry. They were recovered from the electrode surface and identification of the isolates using 16S rRNA sequencing showed that most of them were Gammaproteobacteria, mainly related to Enterobacter and Pseudomonas spp. A CV procedure was designed to check the electrochemical activity of both groups of isolates. Preliminary CVs suggested that the bacteria were not responsible for the catalysis of acetate oxidation. In contrast, both groups of isolates were found to catalyse the electrochemical reduction of oxygen under experimental conditions that favoured adsorption of the microbial cells on the electrode surface.
Conclusions:  Members of the genera Enterobacter and Pseudomonas were found to be able to catalyse the electrochemical reduction of oxygen.
Significance and Impact of the Study:  This study has shown the unexpected efficiency of Enterobacter and Pseudomonas spp. in catalysing the reduction of oxygen, suggesting a possible involvement of these species in biocorrosion, or possible application of these strains in designing bio-cathode for microbial fuel cells.     

Tuning of the FMN binding and oxido-reduction properties by neighboring side chains in Anabaena flavodoxin

Contribution of three regions (phosphate-binding, 50’s and 90’s loops) of Anabaena apoflavodoxin to FMN binding and reduction potential was studied. Thr12 and Glu16 did not influence FMN redox properties, but Thr12 played a role in FMN binding. Replacement of Trp57 with Glu, Lys or Arg moderately shifted E_ox/sq and E_sq/hq and altered the energetic of the FMN redox states binding profile. Our data indicate that the side chain of position 57 does not modulate E_ox/sq by aromatic stacking or solvent exclusion, but rather by influencing the relative strength of the H-bond between the N(5) of the flavin and the Asn58-Ile59 bond. A correlation was observed between the isoalloxazine increase in solvent accessibility and less negative E_sq/hq. Moreover, E_sq/hq became less negative as positively charged residues were added near to the isoalloxazine. Ile59 and Ile92 were simultaneously mutated to Ala or Glu. These mutations impaired FMN binding, while shifting E_sq/hq to less negative values and E_ox/sq to more negative. These effects are discussed on the bases of the X-ray structures of some of the Fld mutants, suggesting that in Anabaena Fld the structural control of both electron transfer steps is much more subtle than in other Flds.