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11.
Niels Peter Revsbech Lars Peter Nielsen Peter Bondo Christensen Jan Srensen 《Applied microbiology》1988,54(9):2245-2249
The construction of a microsensor which can be used to measure O2 and N2O simultaneously is described. The microsensor exhibited a linear response to both O2 and N2O, and the response to N2O was independent of the O2 concentration and vice versa. The N2O detection limit of a microsensor with a tip diameter of 20 μm was around 1 μmol liter−1. The signals for O2 and N2O were affected by hydrogen sulfide, but other interfering agents were not observed in the biofilms and sediments analyzed. Microprofiles of O2 and N2O were measured in a biofilm which was exposed to acetylene to block the N2O reductase activity of denitrifying bacteria. O2 penetrated about 0.5 mm into the biofilm and was not affected by acetylene, but the N2O concentration at 1.4 mm depth increased from 32 to 411 μmol liter−1 after the addition of the inhibitor. The shape of the N2O profile after the addition of acetylene showed that denitrification (denitrifying activity) was detectable in all anoxic layers of the biofilm. 相似文献
12.
The shape of mechanically pierced giant vesicles is studied to obtain the elastic modulus of Gaussian curvature of egg lecithin bilayers. It is argued that such experiments are governed by an apparent modulus, ¯κapp, not the true modulus of Gaussian curvature, ¯κ. A theory of ¯κapp is proposed, regarding the pierced bilayer vesicle as a closed monolayer vesicle. The quantity measured, i.e. ¯κapp/κ, where κ is the rigidity, agrees satisfactorily with the theory. We find ¯κapp = -(1.9 ± 0.3) · 10-12 erg (on the basis of κ = (2.3 ± 0.3) · 10-12 erg). The result may have implications for bilayer fusion. 相似文献
13.
Summary Growth coefficients ofZymomonas mobilis were compared in glucose-limited chemostat culture using a complex medium and a defined minimal growth medium at non inhibitory concentrations of ethanol. Under carbon and energy limited conditions in the complex medium containing yeast extract, the max. molar growth yield (YG
max) and maintenance energy coefficient (me) were 10.8 g cell/mol glucose and 8.3 mmol glu/g cell/hr, respectively. Glucose-limited growth in the minimal medium with NH4Cl as nitrogen source promoted slight energetic uncoupling, as reflected in the decrease in the maximum growth yield. The growth yield with respect to calcium pantothenate was calculated to be 1.4×104 g cell/g Ca-pantothenate. However, pantothenate-limited growth did not result in a decrease in growth yield nor an increase in the specific rate of glucose catabolism. Steady-state growth measurements failed to confirm the previously held view of Belaïchet al. (1972) that pantothenate deficiency induces energetic uncoupling inZymomonas. 相似文献
14.
A crossing programme including 30 species and 40 cytotypes within the genusHordeum was undertaken. Viable hybrids were obtained in 302 combinations, 15 of which were intraspecific. Differences in seed set and in germination were observed in crosses between different groups of species. Obtaining crosses between different taxonomic groups was generally more difficult when diploid material was used. Some species, e.g.,H. lechleri, H. jubatum, andH. brachyantherum showed a higher crossability than others. The chromosome numbers of the hybrids were usually those expected from the parental numbers but aneuploid series around the expected numbers were rather frequent. Three cases of unreduced gametes were found. Selective chromosome elimination was restricted to combinations including eitherH. vulgare orH. bulbosum.—Despite a very diverse morphology, all South American diploid species together with the two North American diploidsH. intercedens andH. pusillum appear to be closely related. The hexaploid American speciesH. procerum, H. lechleri, andH. arizonicum are also related. The two North American tetraploid speciesH. jubatum andH. brachyantherum sometimes form semifertile hybrids. The Asiatic speciesH. roshevitzii appears to be related to both North and South American taxa. 相似文献
15.
Colorless Sulfur Bacteria, Beggiatoa spp. and Thiovulum spp., in O2 and H2S Microgradients 总被引:9,自引:8,他引:1
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The interactions between colorless sulfur bacteria and the chemical microgradients at the oxygen-sulfide interface were studied in Beggiatoa mats from marine sediments and in Thiovulum veils developing above the sediments. The gradients of O2, H2S, and pH were measured by microelectrodes at depth increments of 50 μm. An unstirred boundary layer in the water surrounding the mats and veils prevented microturbulent or convective mixing of O2 and H2S. The two substrates reached the bacteria only by molecular diffusion through the boundary layer. The bacteria lived as microaerophiles or anaerobes even under stirred, oxic water. Oxygen and sulfide zones overlapped by 50 μm in the bacterial layers. Both compounds had concentrations in the range of 0 to 10 μmol liter−1 and residence times of 0.1 to 0.6 s in the overlapping zone. The sulfide oxidation was purely biological. Diffusion calculations showed that formation of mats on solid substrates or of veils in the water represented optimal strategies for the bacteria to achieve a stable microenvironment, a high substrate supply, and an efficient competition with chemical sulfide oxidation. The continuous gliding movement of Beggiatoa cells in mats or the flickering motion of Thiovulum cells in veils were important for the availability of both O2 and H2S for the individual bacteria. 相似文献
16.
17.
Denitrification and oxygen respiration in biofilms studied with a microsensor for nitrous oxide and oxygen 总被引:4,自引:0,他引:4
Lars Peter Nielsen Peter Bondo Christensen Niels Peter Revsbech Jan Sørensen 《Microbial ecology》1990,19(1):63-72
Depth distributions of O2 respiration and denitrification activity were studied in 1- to 2-mm thick biofilms from nutrient-rich Danish streams. Acetylene was added to block the reduction of N2O, and micro-profiles of O2 and N2O in the biofilm were measured simultaneously with a polarographic microsensor. The specific activities of the two respiratory processes were calculated from the microprofiles using a one-dimensional diffusion-reaction model. Denitrification only occurred in layers where O2 was absent or present at low concentrations (of a fewM). Introduction of O2 into deeper layers inhibited denitrification, but the process started immediately after anoxic conditions were reestablished. Denitrification activity was present at greater depth in the biofilm when the NO3
– concentration in the overlying water was elevated, and the deepest occurrence of denitrification was apparently determined by the depth penetration of NO3
–. The denitrification rate within each specific layer was not affected by an increase in NO3
– concentration, and the half-saturation concentration (Km) for NO3
– therefore considered to be low (<25M). Addition of 0.2% yeast extract stimulated denitrification only in the uppermost 0.2 mm of the denitrification zone indicating a very efficient utilization of the dissolved organic matter within the upper layers of the biofilm. 相似文献
18.
A novel type of DNA-binding protein interacts with a conserved sequence in an early nodulin ENOD12 promoter 总被引:3,自引:0,他引:3
19.
Sinapic acid ester metabolism in wild type and a sinapoylglucose-accumulating mutant of arabidopsis. 总被引:3,自引:0,他引:3
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Sinapoylmalate is one of the major phenylpropanoid metabolites that is accumulated in the vegetative tissue of Arabidopsis thaliana. A thin-layer chromatography-based mutant screen identified two allelic mutant lines that accumulated sinapoylglucose in their leaves in place of sinapoylmalate. Both mutations were found to be recessive and segregated as single Mendelian genes. These mutants define a new locus called SNG1 for sinapoylglucose accumulator. Plants that are homozygous for the sng1 mutation accumulate normal levels of malate in their leaves but lack detectable levels of the final enzyme in sinapate ester biosynthesis, sinapoylglucose:malate sinapoyltransferase. A study of wild-type and sng1 seedlings found that sinapic acid ester biosynthesis in Arabidopsis is developmentally regulated and that the accumulation of sinapate esters is delayed in sng1 mutant seedlings. 相似文献
20.
Abstract The stemmata of last–instar Nannochoristalarvae are compound eyes composed of 10 or more ommatidia. Each ommatidium has four Semper cells, four distal and four proximal retinula cells which form a cruciform and layered rhabdom. The ommatidia are separated by epidermal cells (possibly rudimentary pigment cells). Corneal lenses are lacking. At the posterior edge, aberrant stemma units may be present which lack a dioptric apparatus and have a star–shaped rhabdom composed of at least six retinula cells. The stemmata of Nannochoristaappear to be derived from stemmata of the Panorpa-type (Mecoptera-Panorpidae). Differences between the stemmata of Nannochoristaand Panorpacan be explained as adaptations to aquatic life (flat cornea) or as regression. A compound larval eye is ascribed to the ground plan of the Mecoptera sensu latoand is considered a genuine plesiomorphy. The identical basic number (seven) of stemmata in the Neuropteroid/Coleoptera assemblage, Amphiesmenoptera and some Mecoptera (Bittacidae, Boreidae) is attributed to parallel evolution. 相似文献