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101.
Abstract Several approaches have been followed to increase the nitrogenase level in filaments of Anabaena ATCC33047. In a nitrogen-free medium lacking added molybdate and supplemented with 10 mM tungstate, growth was impaired as a result of decreased nitrogenase activity level. Under these conditions, the filaments exhibited nitrogen starvation symptoms and a high heterocyst frequency, with heterocysts being up to 28% of the total number of cells in the filaments, while a regular pattern of heterocyst distribution was maintained. Normal nitrogenase level and nitrogen status were recovered upon molybdate addition, with resumption of growth and decrease of the heterocyst frequency with time until reaching a value of about 10%. The yield of ammonium photoproduction from N2 by filaments displaying different heterocyst frequencies and treated with l -methionine- d,l -sulfoximine (MSX) was determined. Maximal rates were obtained with filaments containing 16% of the cells differentiated as heterocysts. Results indicate that appropriate manipulation of the heterocyst frequency leads to an improvement in the efficiency of conversion of light energy into chemical energy through photoreduction of N2 to ammonium. 相似文献
102.
The cytochrome composition of membrane preparations from 3 thermotolerant species of Streptomyces was determined from difference spectra. All contained b, c and a-type haemoproteins and in addition, 2 species (Streptomyces thermoviolaceus and Streptomyces thermoflavus) possessed cytochrome oxidase d. A CO-reacting b cytochrome similar to cytochrome oxidase o could also be detected in all 3 organisms. Thermotolerance of the respiratory chains showed no correlation with cytochrome composition. In general, Streptomyces thermonitrificans had the most thermostable activities, whilst those of S. thermoviolaceus were the most thermolabile. Growth temperature exerted no qualitative effects on respiratory chain composition but did affect the thermostability of some substrate-supported oxidase activities. 相似文献
103.
Propionibacterium acnes, Propionibacterium avidum and Propionibacterium granulosum were grown in continuous culture at 0–100% air saturation using a semi-synthetic medium. All 3 species utilised oxygen and showed increased growth at 10% air saturation. Oxygen depressed the levels of the fermentation end products propionic and acetic acids. The 3 species differed in the production of ‘oxygen-detoxifying’ enzymes. P. acnes produced catalase, P. avidum produced superoxide dismutase and P. granulosum produced catalase anaerobically and cytochrome c reductase aerobically. The results suggest that under aerobic conditions these bacteria may obtain energy without increased substrate-level phosphorylation and that they may employ different strategies to overcome the toxic effects of oxygen. 相似文献
104.
R. Otto 《FEMS microbiology letters》1986,34(2):191-194
Abstract Gram-negative methylotrophs contain a high- M r 'large' citrate synthase. Gram-positive methylotrophs, on the other hand, contain a 'small' citrate synthase. These differences in M r coincided partly with differences in NADH sensitivity. Citrate synthases from obligate Gram-negative and Gram-positive facultative methylotrophs were insensitive to feedback inhibition by NADH; only the enzymes from Gram-negative facultative methylotrophs were inhibited by NADH. 相似文献
105.
Abstract The effect of increasing concentrations of Ca2+ , Mg2+ , Cu2+ , Zn2+ , Na+ and EDTA on the pectic enzymic activities (polymethylgalacturonase, endopectinase and pectin-lyase) present in the autolytic complex from Alternaria alternata has been studied. In all cases the divalent metal ions and EDTA produced an increased inhibition correlated with increasing concentration of each ion. An opposite effect was shown by the Na+ ion, which produced an increase in pectic enzymic activities, principally at low concentrations. 相似文献
106.
107.
Vales MI Schön CC Capettini F Chen XM Corey AE Mather DE Mundt CC Richardson KL Sandoval-Islas JS Utz HF Hayes PM 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2005,111(7):1260-1270
The limited population sizes used in many quantitative trait locus (QTL) detection experiments can lead to underestimation
of QTL number, overestimation of QTL effects, and failure to quantify QTL interactions. We used the barley/barley stripe rust
pathosystem to evaluate the effect of population size on the estimation of QTL parameters. We generated a large (n=409) population of doubled haploid lines derived from the cross of two inbred lines, BCD47 and Baronesse. This population
was evaluated for barley stripe rust severity in the Toluca Valley, Mexico, and in Washington State, USA, under field conditions.
BCD47 was the principal donor of resistance QTL alleles, but the susceptible parent also contributed some resistance alleles.
The major QTL, located on the long arm of chromosome 4H, close to the Mlo gene, accounted for up to 34% of the phenotypic variance. Subpopulations of different sizes were generated using three methods—resampling,
selective genotyping, and selective phenotyping—to evaluate the effect of population size on the estimation of QTL parameters.
In all cases, the number of QTL detected increased with population size. QTL with large effects were detected even in small
populations, but QTL with small effects were detected only by increasing population size. Selective genotyping and/or selective
phenotyping approaches could be effective strategies for reducing the costs associated with conducting QTL analysis in large
populations. The method of choice will depend on the relative costs of genotyping versus phenotyping.
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
108.
The new species Tinocladia sanrikuensis sp. nov. H.Kawai, K.Takeuchi & T.Hanyuda (Ectocarpales s.l., Phaeophyceae) is described from the Pacific coast of the Tohoku region, northern Japan based on morphology and DNA sequences. The species is a spring–summer annual growing on lower intertidal to upper subtidal rocks and cobbles on relatively protected sites. T. sanrikuensis has a slimy, cylindrical, multiaxial erect thallus, slightly hollow when fully developed, branching once to twice, and resembles T. crassa in gross morphology. The erect thalli are composed of a dense medullary layer, long subcortical filaments, and assimilatory filaments of 11–35 cells, up to 425 μm long and curved in the upper portion. Unilocular zoidangia are formed on the basal part of assimilatory filaments. The species is genetically most closely related to T. crassa and has the same basic thallus structures but differs in having thinner and longer assimilatory filaments. DNA sequences of the mitochondrial cox1 and cox3, chloroplast atpB, psaA, psbA and rbcL genes support the distinctness of this species. 相似文献
109.
I. A. Bryantseva V. M. Gorlenko T. P. Tourova B. B. Kuznetsov A. M. Lysenko S. A. Bykova V. F. Gal’chenko L. L. Mityushina G. A. Osipov 《Microbiology》2000,69(3):325-334
Two new species of heliobacteria isolated from cyanobacterial mats of two alkaline sulfidic hot springs are formally described.
Strains BR4 and BG29 are assigned to anoxygenic phototrophic bacteria of the familyHeliobacteriaceae, since they possess the unique properties of this taxon: strict anaerobiosis, formation of bacteriochlorophyllg, the lack of extensive intracytoplasmic membranes and chlorosomes, an unusual cell wall structure, and phylogenetic relatedness
to the low G+C gram-positive eubacteria. Based on the 16S rDNA sequence similarity, strains BR4 and BG29 are assigned to the
genusHeliobacterium and described as two new species of this genus:Heliobacterium sulfidophilum sp. nov. andHeliobacterium undosum sp. nov. The G+C content of the DNA is 51.3 mol % inHbt. sulfidophilum and 57.2-57.7 mol % inHbt. undosum. The cells ofHbt. sulfidophilum are rods, and the cells ofHbt. undosum are slightly twisted spirilla or short rods. Both new bacteria are motile by peritrichous flagella.Hbt. sulfidophilum produces endospores. The new bacteria are strict anaerobes growing photoheterotrophically on a limited range of organic compounds.
In the dark, they can switch from photosynthesis to the slow fermentation of pyruvate. Biotin is required as a growth factor.
Both species are highly tolerant to sulfide (up to 2 mM at pH 7.5) and oxidize it photoheterotrophically to elemental sulfur;
photoautotrophic growth was not observed. The temperature optimal for growth ofHbt. sulfidophilum andHbt undosum is 30–35‡C, and the optimal pH is 7–8. 相似文献
110.
菌根真菌在红壤中对柑桔吸收磷肥的研究 总被引:2,自引:0,他引:2
接种一种球囊霉 Glomus sp.编号 CC-1于红壤中,使酸桔和枳实生苗的根系感染形成泡囊丛枝内生菌根。应用放射性同位素~(32)P 标记的可溶性磷肥和难溶性磷肥来研究菌根真菌对柑桔吸收磷肥的作用。放射性宏观自显影和显微自显影表明菌根真菌加强了柑桔对两类磷肥的吸收。放射性测量和化学分析证明有菌根柑桔实生苗的地上部含磷量以及从红壤中和从肥料中吸收的磷量比无菌根的增多,有菌根实生苗的生长反应也较好。 相似文献