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81.
Aerobic denitrification: a controversy revived 总被引:37,自引:0,他引:37
During studies on the denitrifying mixotroph, Thiosphaera pantotropha, it has been found that this organism is capable of simultaneously utilizing nitrate and oxygen as terminal electron acceptors in respiration. This phenomenon, termed aerobic denitrification, has been found in cultures maintained at dissolved oxygen concentrations up to 90% of air saturation.The evidence for aerobic denitrification was obtained from a number of independant experiments. Denitrifying enzymes were present even in organisms growing aerobically without nitrate. Aerobic yields on acetate were higher (8.1 g protein/mol) without than with (6.0 g protein/mol) nitrate, while the anaerobic yield with nitrate was even lower (4 g protein/mol). The maximum specific growth rate of Tsa. pantotropha was higher (0.34 h-1) in the presence of both oxygen (>80% air saturation) and nitrate than in similar cultures not supplied with nitrate (0.27 h-1), indicating that the rate of electron transport to oxygen was limiting. This was confirmed by oxygen uptake experiments which showed that although the rate of respiration on acetate was not affected by nitrate, the total oxygen uptake was reduced in its presence. The original oxygen uptake could be restored by the addition of denitrification inhibitors.Dedicated to Professor Dr. H.-G. Schlegel on the occasion of his 60th birthday 相似文献
82.
The orientation of pigments and pigment-protein complexes of the green photosynthetic bacterium Prosthecochloris aestuarii was studied by measurement of linear dichroism spectra at 295 and 100 K. Orientation of intact cells and membrane vesicles (Complex I) was obtained by drying on a glass plate. The photochemically active pigment-protein complexes (photosystem-protein complex and reaction center pigment-protein complex) and the antenna bacteriochlorophyll a protein were oriented by pressing a polyacrylamide gel. The data indicate that the near-infrared transitions (Qy) of bacteriochlorophyll c and most bacteriochlorophyll a molecules have a relatively parallel orientation to the membrane, whereas the Qy transitions of the bacteriochlorophyll a in the antenna protein are oriented predominantly perpendicularly to the membrane. Carotenoids and the Qx transitions (590–620 nm) of bacteriochlorophyll a, not belonging to the bacteriochlorophyll a protein, have a relatively perpendicular orientation to the membrane. The absorption and linear dichroism spectra indicate the existence of different pools of bacteriochlorophyll c in the chlorosomes and of carotenoid and bacteriopheophytin c in the cell membrane. The results suggest that the photosystem-protein and reaction center pigment-protein complexes are oriented with their short axes approximately perpendicular to the plane of the membrane. The symmetry axis of the bacteriochlorophyll a protein has an approximately perpendicular orientation. 相似文献
83.
Ikuya Yano Sadao Imaizumi Ikuko Tomiyasu Eiko Yabuuchi 《FEMS microbiology letters》1983,20(3):449-453
Abstract The occurrence of free ceramides was shown in the chloroform-methanol extractable lipids of 16 strains of Sphingobacterium including three species: S. versatilis, S. multivorum and S. mizutae . The predominant long-chain base was identified as a branched-chain, saturated dihydroxy base with a carbon chain consisting of 17 carbon atoms, while the most abundant fatty acid was 2-hydroxy-13-methyltetradecanoic acid. The major molecular species of the intact ceramides were identified as LCB- d - iso -17 : 0-2-OH iso -15 : 0FA, LCB- d - iso -17 : 0- iso -15 : 0FA and LCB- d -n16 : 0- iso -15 : 0FA. 相似文献
84.
Whole cells and isolated chlorosomes (antenna complex) of the green photosynthetic bacterium Chloroflexus aurantiacus have been studied by absorption spectroscopy (77 K and room temperature), fluorescence spectroscopy, circular dichroism, linear dichroism and electron spin resonance spectroscopy. The chlorosome absorption spectrum has maxima at 450 (contributed by carotenoids and bacteriochlorophyll (BChl) a Soret), 742 (BChl c) and 792 nm (BChl a) with intensity ratios of 20:25. The fluorescence emission spectrum has peaks at 748 and 802 nm when excitation is into either the 742 or 450 nm absorption bands, respectively. Whole cells have fluorescence peaks identical to those in chlorosomes with the addition of a major peak observed at 867 nm. The CD spectrum of isolated chlorosomes has an asymmetric-derivative-shaped CD centered at 739 nm suggestive of exciton interaction at least on the level of dimers. Linear dichroism of oriented chlorosomes shows preferential absorption at 742 nm of light polarized parallel to the long axis of the chlorosome. This implies that the transition dipoles are also oriented more or less parallel to the long axis of the chlorosome. Treatment with ferricyanide results in the appearance of a 2.3 G wide ESR spectrum at g 2.002. Whole cells grown under different light conditions exhibit different fluorescence behavior when absorption is normalized at 742 nm. Cells grown under low light conditions have higher fluorescence intensity at 748 nm and lower intensity at 802 nm than cells grown under high light conditions. These results indicate that the BChl c in chlorosomes is highly organized, and transfers energy from BChl c (742 nm) to a connector of baseplate BChl B792 (BChl a) presumably located in the chlorosome baseplate adjacent to the cytoplasmic membrane. 相似文献
85.
J. D. Barbour R. R. Farrar G. G. Kennedy 《Entomologia Experimentalis et Applicata》1991,60(3):289-300
The effect of fertilizer regime on trichome- and lamellar-based resistance in the wild tomato species, Lycopersicon hirsutum f. glabratum C.H. Mull accession PI 134417, to three insect pests of tomato, the tobacco hornworm, Manduca sexta (L.), the colorado potato beetle, Leptinotarsa decemlineata (Say), and the tomato fruitworm, Heliocoverpa zea (Boddie), was examined. Increasing the rate at which NPK fertilizer was applied, from 1.8 to 19.6 g/plant/week, reduced the trichome-based resistance of PI 134417 to M. sexta and L. decemlineata by lowering both the density of type VI (sensu Luckwill, 1943) glandular trichomes and the amount of 2-tridecanone contained in the tips of these trichomes. 2-Tridecanone is a toxic methyl-ketone responsible for glandular trichome-mediated resistance in PI 134417 to M. sexta and L. decemlineata. A similar increase in the application rate of NPK fertilizer reduced the lamellarbased resistance of PI 134417 to L. decemlineata and H. zea. The meachanisms for this reduction of resistance are unknown, but may be related to improved nutritional quality of hosts at higher fertilizer regimes. 相似文献
86.
The inhibition of membrane ATPase from the marine alkalotolerant bacterium Vibrio alginolyticus by DCCD, triphenyltin and venturicidin was studied. DCCD proved to be an irreversible inhibitor, while venturicidin and triphenyltin produced a reversible inhibitory effect. The DCCD-binding proteolipid was identified in the membrane preparations. The effect of the inhibitors on ATPase activity and ATP-dependent Na+-transport in V. alginolyticus subcellular vesicles is discussed. 相似文献
87.
88.
慢性扁桃体炎与细菌L型感染 总被引:1,自引:0,他引:1
通常认为,慢性扁桃体炎主要致病菌是金黄色葡萄球菌和乙型溶血性链球菌。通过50例慢性扁桃体炎的病原微生物培养、组织切片细菌学及电镜等研究,发现慢性扁桃体炎组织中细菌L型也相当常见,L型培养阳性率是88.5%,且组织切片L型感染率与培养阳性率基本一致(P>0.05)。电镜在扁桃体组织间质及上皮细胞、淋巴细胞等多种细胞内均见到细菌L型。提示慢性扁桃体炎与细菌L型感染关系极为密切。并认为,L型侵入组织并在宿主细胞内生长的特性,可能是慢性扁桃体炎反复发作、迁延不愈的重要原因。 相似文献
89.
The economic and environmental costs of the heavy use of chemical N fertilizers in agriculture are a global concern. Sustainability considerations mandate that alternatives to N fertilizers must be urgently sought. Biological nitrogen fixation (BNF), a microbiological process which converts atmospheric nitrogen into a plant-usable form, offers this alternative. Nitrogen-fixing systems offer an economically attractive and ecologically sound means of reducing external inputs and improving internal resources. Symbiotic systems such as that of legumes and Rhizobium can be a major source of N in most cropping systems and that of Azolla and Anabaena can be of particular value to flooded rice crop. Nitrogen fixation by associative and free-living microorganisms can also be important. However, scientific and socio-cultural constraints limit the utilization of BNF systems in agriculture. While several environmental factors that affect BNF have been studied, uncertainties still remain on how organisms respond to a given situation. In the case of legumes, ecological models that predict the likelihood and the magnitude of response to rhizobial inoculation are now becoming available. Molecular biology has made it possible to introduce choice attributes into nitrogen-fixing organisms but limited knowledge on how they interact with the environment makes it difficult to tailor organisms to order. The difficulty in detecting introduced organisms in the field is still a major obstacle to assessing the success or failure of inoculation. Production-level problems and socio-cultural factors also limit the integration of BNF systems into actual farming situations. Maximum benefit can be realized only through analysis and resolution of major constraints to BNF performance in the field and adoption and use of the technology by farmers. 相似文献
90.
Below-ground carbon distribution in barley (Hordeum vulgare L.) with and without nitrogen fertilization 总被引:5,自引:0,他引:5
Gerd Johansson 《Plant and Soil》1992,144(1):93-99
The distribution of net assimilated C in barley (Hordeum vulgare L.) grown at two N-levels was determined in a growth chamber. The N-fertilization involved 0 and 3.61 mol N g-1 dry soil. After growth for seven weeks in an atmosphere with continuously 14C-labelled CO2, 14C was determined in shoots, roots, rhizosphere respiration and soil. At the low N-level, 32% of the net assimilated 14C was translocated below ground, whereas at the high N-level 27% was translocated below ground. The release of C from roots (root respiration, microbial respiration originating from decomposition of 14C-labelled root material and 14C remaining in soil) was greater with no N-supply (19% of net assimilated 14C) than in the treatment with N-supply (15%). Thus, the effect of N-supply on both translocation of assimilated 14C below ground and the release of 14C from growing roots was relatively small. 相似文献