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Methanococcus maripaludis is an anaerobic, methane-producing archaeon that utilizes H2 or formate for the reduction of CO2 to methane. Tryptophan auxotrophs were constructed by in vitro insertions of the Tn5 transposon into the tryptophan operon, followed by transformation into M. maripaludis . This method could serve for rapid insertions into large cloned DNA regions. 相似文献
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The leptospira cbiC encodes the enzyme catalyzing the methyl rearrangement reaction of the cobalamin biosynthesis pathway. The protein has been cloned and overexpressed as a His-tagged recombinant protein in Escherichia coli. The crystal structures have been solved in two crystal forms (P4(2)2(1)2 and P3(1)21) diffracting to 3.0 and 2.3A resolution, respectively. The structures are similar to the precorrin-8x methyl mutase (CobH), an enzyme of the aerobic pathway to vitamin B12. 相似文献
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Role of amino acids, betaine and choline in vitamin B12 biosynthesis by strains of Propionibacterium
This paper reports the role of amino acids, betaine and choline on vitamin B12 biosynthesis in Propionibacterium shermanii 566, P. shermanii and Propionibacterium arl AKU 1251. l-Glutamic acid supplemented at the 0.05% (w/v) level in whey permeate stimulated vitamin B12 production in the three organisms, whereas the influence of other amino acids differed in the three strains. A uniform increase in product formation in Propionibacterium cultures with increasing doses of betaine and choline was recorded, but with variable relative effectiveness. However, no significant difference at the 0.50 and 0.75% (w/v) levels of these two compounds was observed. The addition of betaine at 0.5% (w/v) concentration was considered optimal for maximum fermentation efficiency in the cultures. An increase of 2.8–25.7% and 5.1–40.8% in vitamin B12 yield as compared to the control was observed by supplementing whey permeate medium with l-glutamic acid and betaine, respectively, at their optimum values in the organisms studied. 相似文献
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维生素B12(VB12)是一种重要的动物和人类营养因子, 广泛应用于饲料、食品和医药卫生领域。中国已成为全球VB12的主要产地, 2007年产量为27 t, 占全球总产量的77%。VB12是目前已发现的最大、最复杂的维生素分子, 化学合成极其困难, 所有VB12产品均采用生物发酵制备其主体结构。VB12主要由古生菌和一些真细菌通过有氧或厌氧两种途径合成, 工业上主要采用费式丙酸菌(Propionibacterium freudenrechii)和脱氮假单胞菌(Pseudomonas denitrificans)进行发酵生产。综述了VB12的基本性质, 生物合成途径, 以及发酵生产工艺, 并对VB12的应用与市场前景作了分析。 相似文献
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维生素B12(VB12)是一种重要的动物和人类营养因子, 广泛应用于饲料、食品和医药卫生领域。中国已成为全球VB12的主要产地, 2007年产量为27 t, 占全球总产量的77%。VB12是目前已发现的最大、最复杂的维生素分子, 化学合成极其困难, 所有VB12产品均采用生物发酵制备其主体结构。VB12主要由古生菌和一些真细菌通过有氧或厌氧两种途径合成, 工业上主要采用费式丙酸菌(Propionibacterium freudenrechii)和脱氮假单胞菌(Pseudomonas denitrificans)进行发酵生产。综述了VB12的基本性质, 生物合成途径, 以及发酵生产工艺, 并对VB12的应用与市场前景作了分析。 相似文献
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Genetics in methanogens: transposon insertion mutagenesis of a Methanococcus maripaludis nifH gene. 总被引:6,自引:2,他引:4 下载免费PDF全文
We designed a transposon insertion mutagenesis system for Methanococcus species and used it to make mutations in and around a nifH gene in Methanococcus maripaludis. The transposon Mudpur was constructed with a gene for puromycin resistance that is expressed and selectable in Methanococcus species. A 15.6-kb nifH region from M. maripaludis cloned in a lambda vector was used as a target for mutagenesis. A series of 19 independent Mudpur insertions spanning the cloned region were produced. Four mutagenized clones in and around nifH were introduced by transformation into M. maripaludis, where each was found to replace wild-type genomic DNA with the corresponding transposon-mutagenized DNA. Wild-type M. maripaludis and a transformant containing a Mudpur insertion upstream of nifH grew on N2 as a nitrogen source. Two transformants with insertions in nifH and one transformant with an insertion downstream of nifH did not grow on N2. The transposon insertion-gene replacement technique should be generally applicable in the methanococci for studying the effects of genetic manipulations in vivo. 相似文献
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Ribose biosynthesis and evidence for an alternative first step in the common aromatic amino acid pathway in Methanococcus maripaludis. 总被引:1,自引:0,他引:1 下载免费PDF全文
An acetate-requiring mutant of Methanococcus maripaludis allowed efficient labeling of riboses following growth in minimal medium supplemented with [2-(13)C]acetate. Nuclear magnetic resonance and mass spectroscopic analysis of purified cytidine and uridine demonstrated that the C-1' of the ribose was about 67% enriched for 13C. This value was inconsistent with the formation of erythrose 4-phosphate (E4P) exclusively by the carboxylation of a triose. Instead, these results suggest that either (i) E4P is formed by both the nonoxidative pentose phosphate and triose carboxylation pathways or (ii) E4P is formed exclusively by the nonoxidative pentose phosphate pathway and is not a precursor of aromatic amino acids. 相似文献
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Hydrogenase-independent uptake and metabolism of electrons by the archaeon Methanococcus maripaludis
Svenja T Lohner J?rg S Deutzmann Bruce E Logan John Leigh Alfred M Spormann 《The ISME journal》2014,8(8):1673-1681
Direct, shuttle-free uptake of extracellular, cathode-derived electrons has been postulated as a novel mechanism of electron metabolism in some prokaryotes that may also be involved in syntrophic electron transport between two microorganisms. Experimental proof for direct uptake of cathodic electrons has been mostly indirect and has been based on the absence of detectable concentrations of molecular hydrogen. However, hydrogen can be formed as a transient intermediate abiotically at low cathodic potentials (<−414 mV) under conditions of electromethanogenesis. Here we provide genetic evidence for hydrogen-independent uptake of extracellular electrons. Methane formation from cathodic electrons was observed in a wild-type strain of the methanogenic archaeon Methanococcus maripaludis as well as in a hydrogenase-deletion mutant lacking all catabolic hydrogenases, indicating the presence of a hydrogenase-independent mechanism of electron catabolism. In addition, we discovered a new route for hydrogen or formate production from cathodic electrons: Upon chemical inhibition of methanogenesis with 2-bromo-ethane sulfonate, hydrogen or formate accumulated in the bioelectrochemical cells instead of methane. These results have implications for our understanding on the diversity of microbial electron uptake and metabolism. 相似文献
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Inactivation of the selB gene in Methanococcus maripaludis: effect on synthesis of selenoproteins and their sulfur-containing homologs 下载免费PDF全文
The genome of Methanococcus maripaludis harbors genes for at least six selenocysteine-containing proteins and also for homologs that contain a cysteine codon in the position of the UGA selenocysteine codon. To investigate the synthesis and function of both the Se and the S forms, a mutant with an inactivated selB gene was constructed and analyzed. The mutant was unable to synthesize any of the selenoproteins, thus proving that the gene product is the archaeal translation factor (aSelB) specialized for selenocysteine insertion. The wild-type form of M. maripaludis repressed the synthesis of the S forms of selenoproteins, i.e., the selenium-independent alternative system, in selenium-enriched medium, but the mutant did not. We concluded that free selenium is not involved in regulation but rather a successional compound such as selenocysteyl-tRNA or some selenoprotein. Apart from the S forms, several enzymes from the general methanogenic route were affected by selenium supplementation of the wild type or by the selB mutation. Although the growth of M. maripaludis on H(2)/CO(2) is only marginally affected by the selB lesion, the gene is indispensable for growth on formate because M. maripaludis possesses only a selenocysteine-containing formate dehydrogenase. 相似文献
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