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101.
Bacterial growth under oxygen‐limited (microaerobic) conditions is often accompanied by phenomena of great interest for fundamental research and industrial application. The microaerobic lifestyle of anoxygenic photosynthetic bacteria like Rhodospirillum rubrum harbors such a phenomenon, as it allows the formation of photosynthetic membranes and related interesting products without light. However, due to the technical difficulties in process control of microaerobic cultivations and the limited sensitivity of available oxygen sensors, the analysis of microaerobic growth and physiology is still underrepresented in current research. The main focus of the present study was to establish an experimental set‐up for the systematic study of physiological processes, associated with the growth of R. rubrum under microaerobic conditions in the dark. For this purpose, we introduce a robust and reliable microaerobic process control strategy, which applies the culture redox potential (CRP) for assessing different degrees of oxygen limitation in bioreactor cultivations. To describe the microaerobic growth behavior of R. rubrum cultures for each of these defined CRP reduction steps, basic growth parameters were experimentally determined. Flux variability analysis provided an insight into the metabolic activity of the TCA cycle and implied its connection to the respiratory capacity of the cells. In this context, our results suggest that microaerobic growth of R. rubrum can be described as an oxygen‐activated cooperative mechanism. The present study thus contributes to the investigation of metabolic and regulatory events responsible for the redox‐sensitive formation of photosynthetic membranes in facultative photosynthetic bacteria. Furthermore, the introduced microaerobic cultivation setup should be generally applicable for any microbial system of interest which can be cultivated in common stirred‐tank bioreactors. Biotechnol. Bioeng. 2013; 110: 573–585. © 2012 Wiley Periodicals, Inc. 相似文献
102.
Kathleen G. Dwyer Martin T. Berger Rimsha Ahmed Molly K. Hritzo Amanda A. McCulloch Michael J. Price Nicholas J. Serniak Leonard T. Walsh June B. Nasrallah Mikhail E. Nasrallah 《Genetics》2013,193(3):985-994
The switch from an outcrossing mode of mating enforced by self-incompatibility to self-fertility in the Arabidopsis thaliana lineage was associated with mutations that inactivated one or both of the two genes that comprise the self-incompatibility (SI) specificity-determining S-locus haplotype, the S-locus receptor kinase (SRK) and the S-locus cysteine-rich (SCR) genes, as well as unlinked modifier loci required for SI. All analyzed A. thaliana S-locus haplotypes belong to the SA, SB, or SC haplotypic groups. Of these three, the SC haplotype is the least well characterized. Its SRKC gene can encode a complete open-reading frame, although no functional data are available, while its SCRC sequences have not been isolated. As a result, it is not known what mutations were associated with inactivation of this haplotype. Here, we report on our analysis of the Lz-0 accession and the characterization of its highly rearranged SC haplotype. We describe the isolation of its SCRC gene as well as the subsequent isolation of SCRC sequences from other SC-containing accessions and from the A. lyrata S36 haplotype, which is the functional equivalent of the A. thaliana SC haplotype. By performing transformation experiments using chimeric SRK and SCR genes constructed with SC- and S36-derived sequences, we show that the SRKC and SCRC genes of Lz-0 and at least a few other SC-containing accessions are nonfunctional, despite SCRC encoding a functional full-length protein. We identify the probable mutations that caused the inactivation of these genes and discuss our results in the context of mechanisms of S-locus inactivation in A. thaliana. 相似文献
103.
Neil W. Blackstone 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2013,368(1622)
According to multi-level theory, evolutionary transitions require mediating conflicts between lower-level units in favour of the higher-level unit. By this view, the origin of eukaryotes and the origin of multicellularity would seem largely equivalent. Yet, eukaryotes evolved only once in the history of life, whereas multicellular eukaryotes have evolved many times. Examining conflicts between evolutionary units and mechanisms that mediate these conflicts can illuminate these differences. Energy-converting endosymbionts that allow eukaryotes to transcend surface-to-volume constraints also can allocate energy into their own selfish replication. This principal conflict in the origin of eukaryotes can be mediated by genetic or energetic mechanisms. Genome transfer diminishes the heritable variation of the symbiont, but requires the de novo evolution of the protein-import apparatus and was opposed by selection for selfish symbionts. By contrast, metabolic signalling is a shared primitive feature of all cells. Redox state of the cytosol is an emergent feature that cannot be subverted by an individual symbiont. Hypothetical scenarios illustrate how metabolic regulation may have mediated the conflicts inherent at different stages in the origin of eukaryotes. Aspects of metabolic regulation may have subsequently been coopted from within-cell to between-cell pathways, allowing multicellularity to emerge repeatedly. 相似文献
104.
Redox Shuttles with Axisymmetric Scaffold for Overcharge Protection of Lithium‐Ion Batteries
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The derivatives of 1,4‐dimethoxybenzene are thus far the best performing redox shuttle additives for overcharge protection of Li‐ion batteries. The most durable molecules of this kind typically possess two in‐plane methoxy groups that are equivalent by inversion symmetry. However, such geometry leads to a vanishing average dipole moment that causes poor solubility of these molecules in carbonate‐based electrolytes. In this study, a novel redox shuttle additive, 1,2,3,4‐tetrahydro‐6,7‐dimethoxy‐1,1,4,4‐tetramethyl‐naphthalene (TDTN), is introduced. It has been demonstrated that reversible oxidation at 4.05 V versus Li+/Li, high polarity, high solubility (around 0.4 m ), and excellent electrochemical stability (150 overcharge cycles at C/2 rate with 100% overcharge) can all be achieved simultaneously by the imposition of axial symmetry in the corresponding radical cation that is generated by electrochemical oxidation of TDTN in the battery. The intricate interplay between the symmetry and the chemical stability of the radical cation is scrutinized using magnetic resonance spectroscopy and electron structure modeling. 相似文献
105.
A new concept of multiple redox semi‐solid‐liquid (MRSSL) flow battery that takes advantage of active materials in both liquid and solid phases, is proposed and demonstrated. Liquid lithium iodide (LiI) electrolyte and solid sulfur/carbon (S/C) composite, forming LiI‐S/C MRSSL catholyte, are employed to demonstrate this concept. Record volumetric capacity (550 Ah L?1catholyte) is achieved using highly concentrated and synergistic multiple redox reactions of LiI and sulfur. The liquid LiI electrolyte is found to increase the reversible volumetric capacity of the catholyte, improve the electrochemical utilization of the S/C composite, and reduce the viscosity of catholyte. A continuous flow test is demonstrated and the influence of the flow rate on the flow battery performance is discussed. The MRSSL flow battery concept transforms inactive component into bi‐functional active species and creates synergistic interactions between multiple redox couples, offering a new direction and wide‐open opportunities to develop high‐energy‐density flow batteries. 相似文献
106.
Mansi Gupta Anja Machate Daniela Zöller Michael Brand 《Genesis (New York, N.Y. : 2000)》2016,54(1):19-28
Gene trapping has emerged as a valuable tool to create conditional alleles in various model organisms. Here we report the FLEx‐based gene trap vector SAGFLEx that allows the generation of conditional mutations in zebrafish by gene‐trap mutagenesis. The SAGFLEx gene‐trap cassette comprises the rabbit β‐globin splice acceptor and the coding sequence of GFP, flanked by pairs of inversely oriented heterotypic target sites for the site‐specific recombinases Cre and Flp. Insertion of the gene‐trap cassette into endogenous genes can result in conditional mutations that are stably inverted by Cre and Flp, respectively. To test the functionality of this system we performed a pilot screen and analyzed the insertion of the gene‐trap cassette into the lima1a gene locus. In this lima1a allele, GFP expression faithfully recapitulated the endogenous lima1a expression and resulted in a complete knockout of the gene in homozygosity. Application of either Cre or Flp was able to mediate the stable inversion of the gene trap cassette and showed the ability to conditionally rescue or reintroduce the gene inactivation. Combined with pharmacologically inducible site specific recombinases the SAGFLEx vector insertions will enable precise conditional knockout studies in a spatial‐ and temporal‐controlled manner. genesis 54:19–28, 2016. © 2015 Wiley Periodicals, Inc. 相似文献
107.
108.
Radka Vladkova 《Journal of biomolecular structure & dynamics》2016,34(4):824-854
The cytochrome (cyt) b6f complex is involved in the transmembrane redox signaling that triggers state transitions in cyanobacteria and chloroplasts. However, the components and molecular mechanisms are still unclear. In an attempt to solve this long-standing problem, we first focused on the unknown role of a single chlorophyll a (Chla) in cyt b6f with a new approach based on Chla structural properties. Various b6f X-ray crystal structures were analyzed to identify their differences, which correlate with differences in Chla molecular volume. We found that the distance of the Rieske [2Fe-2S] cluster to Chla correlates with the distance between a pair of residues at the Qo-site and the distance between a pair of residues at the opposite membrane side. These correlations were accompanied by the rotation of a key peripheral residue and by changes in the hydrophobic thickness of cyt b6f. Parallel analysis of cyt bc1 crystal structures allowed us to conclude that Chla acts as the crucial redox sensor and transmembrane signal transmitter in b6f for changes in the plastoquinone pool redox state. The hydrophobic mismatch induced by the changed hydrophobic thickness of cyt b6f is the driving force for the structural reorganizations of the photosynthetic apparatus during induction and the progression of state transitions in cyanobacteria and chloroplasts. A mechanism for LHCII kinase activation in chloroplasts is also proposed. Our understanding of the dynamic structural changes in bc-complexes during turnover at the Qo-site and state transitions is augmented by the time-sequence ordering of 56 bc crystal structures. 相似文献
109.
110.
Ras原癌基因编码的蛋白是细胞信号转导中不可或缺的分子开关,在细胞增殖、分化、凋亡等生理过程中起着重要的作用。Ras基因的功能获得性突变是肿瘤发生和发展的重要驱动因素,因此多年来人们一直致力于靶向Ras蛋白的抗肿瘤药物研究。简介Ras的结构与功能及其与肿瘤的相关性,着重综述近年来靶向Ras的小分子抑制剂的研究进展。 相似文献