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11.
12.
Soils contain two different activities for oxidation of hydrogen 总被引:1,自引:0,他引:1
Abstract Hydrogen oxidation rates were measured in a neutral compost soil and an acidic sandy loam at H2 mixing ratios of 0.01 to 5000 ppmv. The kinetics were biphasic showing two different K m values for H2 , one at about 10–40 nM dissolved H2 , the other at about 1.2–1.4 μM H2 . The low- K m activity was less sensitive to chloroform fumigation than the high- K m activity. If sterile soil was amended with Paracoccus denitrificans or a H2 -oxidizing strain isolated from compost soil, it exhibited only a high- K m (0.7–0.9 μM) activity. It also failed to utilize H2 mixing ratios below a threshold of 1.6–3.0 ppmv H2 (160–300 mPa). A similar result was obtained when fresh soil samples were suspended in water, and H2 oxidation was determined from the decrease of dissolved H2 . However, H2 was again utilized to mixing ratios lower than 0.05 ppmv, if the supernatant of the soil suspension or the settled soil particles were dried onto sterile soil or purified quarz sand. Obviously, soils contain two different activities for oxidation of H2 : (1) a high- K m , high-threshold activity which apparently is due to aerobic H2 -oxidizing bacteria, and (2) a low- K m , low-threshold activity whose origin is unknown but presumably is due to soil enzymes. 相似文献
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14.
Sallie W. Chisholm Sheila L. Frankel Ralf Goericke Robert J. Olson Brian Palenik John B. Waterbury Lisa West-Johnsrud Erik R. Zettler 《Archives of microbiology》1992,157(3):297-300
Several years ago, prochlorophyte picoplankton were discovered in the N. Atlantic. They have since been found to be abundant within the euphotic zone of the world's tropical and temperate oceans. The cells are extremely small, lack phycobiliproteins, and contain divinyl chlorophyll a and b as their primary photosynthetic pigments. Phylogenies constructed from DNA sequence data indicate that these cells are more closely related to a cluster of marine cyanobacteria than to their prochlorophyte relatives Prochlorothrix and Prochloron. Several strains of this organism have recently been brought into culture, and herewith are given the name Prochlorococcus marinus. 相似文献
15.
Metabolism of nitric oxide and nitrous oxide during nitrification and denitrification in soil at different incubation conditions 总被引:1,自引:0,他引:1
Abstract NO production and consumption rates as well as N2 O accumulation rates were measured in a loamy cambisol which was incubated under different conditions (i.e. soil moisture content, addition of nitrogen fertilizer and/or glucose, aerobic or anaerobic gas phase). Inhibition of nitrification with acetylene allowed us to distinguish between nitrification and denitrification as sources of NO and N2 O. Under aerobic conditions untreated soil showed very low release of NO and N2 O but high consumption of NO. Fertilization with NH4 + or urea stimulated both NO and N2 O production by nitrification. Addition of glucose at high soil moisture contents led to increased N2 and N2 O production by denitrification, but not to increased NO production rates. Anaerobic conditions, however, stimulated both NO and N2 O production by denitrification. The production of NO and N2 O was further stimulated at low moisture contents and after addition of glucose or NO3 − . Anaerobic consumption of NO by denitrification followed Michaelis-Menten kinetics and was stimulated by addition of glucose and NO3 − . Aerobic consumption of NO followed first-order kinetics up to mixing ratios of at least 14 ppmv NO, was inhibited by autoclaving but not by acetylene, and decreased with increasing soil moisture content. The high NO-consumption activity and the effects of soil moisture on the apparent rates of anaerobic and aerobic production and consumption of NO suggest that diffusional constraints have an important influence on the release of NO, and may be a reason for the different behaviour of NO release vs N2 O release. 相似文献
16.
Armin Bohmann Ralf Pörtner Jörg Schmieding Volker Kasche Herbert Märkl 《Cytotechnology》1992,9(1-3):51-57
A hybridoma cell was cultivated continuously in a membrane dialysis bioreactor with an integrated radial-flow fixed bed consisting of porous Siran® carriers over a period of 6 weeks. Antibodies accumulated to an average of 100 mg l?1, approx. 10 times more than in fixed bed cultures without dialysis membrane. Serum costs could be reduced about 85% due to an appropriate feeding strategy. Siran® carriers with 3–5 mm diameter showed an advantage compared to those with 1–2 mm diameter. For the 3–5 mm carrier the specific glucose uptake rate and the MAb production rate were constant, if the velocity was between 0.09 mm s?1 and 0.75 mm s?1. At higher velocities cells are washed out of the bed. Furthermore antibody consistency and cell stability were verified in long-term cultivations over a period of 96 days. From an estimation of the antibody concentration reachable with the reactor concept under optimal conditions a concentration 45 times higher compared to axial-flow fixed bed reactors and 11 times higher compared to stirred tank reactors can be expected. 相似文献
17.
Ralf Schmidt Klaus Neubert Alfred Barth Claus Liebmann Martin Schnittler Nga N. Chung Peter W. Schiller 《Peptides》1991,12(6):1175-1180
Cyclic analogues of the β-casein-derived opioid peptide β-casomorphin-5 (H-Tyr-Pro-Phe-Pro-Gly-OH) were prepared through substitution of the Pro2 residue with various ,ω-diamino acid residues (lysine, ornithine, 2,4-diaminobutyric acid) and cyclization of the ω-amino group to the C-terminal carboxyl function. Compounds of this type, with D-configuration at the 2-position residue, showed high opioid receptor affinity with some preference for μ receptors over δ receptors, high potency in the guinea pig ileum assay and considerable activity in the mouse vas deferens assay. Configurational inversion at the 4-position in these cyclic analogues resulted in enhanced affinity for both μ and δ receptors, whereas N-methylation of the Phe3 residue produced a potency decrease. 相似文献
18.
In a previous work (Kömen et al. 1991) it has been concluded that membrane fragments isolated from autotrophically grown Alcaligenes eutrophus H16 contain several iron-sulphur centres along with haems of a-, b-, c-, and d-type. These redox components have been proposed to be part of a branched respiratory chain leading to multiple membrane bound oxidases. Here, some of the respiratory activities catalyzed by membrane fragments from wild type cells of A. eutrophus (H16) and, for comparison, Paracoccus denitrificans, have been investigated through the use of electron transport inhibitors. Cyanide (CN-) titration curves indicated that in A. eutrophus H16 oxidation of succinate and H2 preferentially proceeds via the cytochrome c oxidase(s) branch (I 50=2 · 10-5 M) whereas the NADH dependent respiration started being inhibited at higher CN- concentrations (I 50=5 · 10-4 M). In membranes isolated from both, cells harvested at late growth-phase (OD 12) and from a mutant deficient in cytochrome c oxidase activity (A. eutrophus RK1), respiration was insensitive to low CN- concentrations (< 10-4 M), and it was sustained by the high catalytic activities of two quinol oxidases. These alternative oxidases of b- (formally o-) and d-type showed different sensitivities to KCN (I 50=10-3 M and 10-2 M, respectively). Interestingly, the cytochrome c oxidase(s) dependent respiration of H16 membranes was insensitive to antimycin A but largely inhibited by myxothiazol (10-6 M). This, and previous work (Kömen et al. 1991), suggest that although the respiratory chain of A. eutrophus is endowed with a putative bc 1 complex, its biochemical nature and role in respiration of this organism are apparently different from those of P. denitrificans. The peculiarity of the respiratory chain of A. eutrophus is confirmed by the rotenone insensitivity of the NADH oxidation in both protoplasts and membrane fragments from wild type and soluble hydrogenase deficient cells (HF14 and HF160). A tentative model of the respiratory chain of autotrophically grown A. eutrophus is presented. 相似文献
19.
Oliver Klimmek Achim Kröger Ralf Steudel Gabriele Holdt 《Archives of microbiology》1991,155(2):177-182
Polysulphide was formed according to reaction (1), when tetrathionate was (1) $${\text{S}}_4 {\text{O}}_6^{2 - } + {\text{HS}}^ - \to 2{\text{S}}_2 {\text{O}}_3^{2 - } + {\text{S(O)}} + {\text{H}}^ + $$ added to an anaerobic buffer (pH 8.5) containing excess sulphide. S(O) denotes the zero oxidation state sulphur in the polysulphide mixture S infn sup2- . The addition of formate to the polysulphide solution in the presence of Wolinella succinogenes caused the reduction of polysulphide according to reaction (2). The bacteria grew in a medium containing formate and sulphide, (2) $${\text{HCO}}_2^ - + {\text{S(O)}} + {\text{H}}2{\text{O}} \to {\text{HCO}}_3^ - + {\text{HS}}^ - + {\text{H}}^ + $$ when tetrathionate was continuously added. The cell density increased proportional to reaction (3) which represents the sum of reactions (1) and (3) $${\text{HCO}}_2^ - + {\text{S}}_{\text{4}} {\text{O}}_6^{2 - } + {\text{H}}2{\text{O}} \to {\text{HCO}}_3^ - + 2{\text{S}}_{\text{2}} {\text{O}}_3^{2 - } + 2{\text{H}}^ + $$ (2). The cell yield per mol formate was nearly the same as during growth on formate and elemental sulphur, while the velocity of growth was greater. The specific activities of polysulphide reduction by formate measured with bacteria grown with tetrathionate or with elemental sulphur were consistent with the growth parameters. The results suggest that W. succinogenes grow at the expense of formate oxidation by polysulphide and that polysulphide is an intermediate during growth on formate and elemental sulphur. 相似文献
20.