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TL Kieft EM Murphy DL Haldeman PS Amy BN Bjornstad EV McDonald DB Ringelberg DC White J Stair RP Griffiths TC Gsell WE Holben DR Boone 《Microbial ecology》1998,36(3):336-348
Abstract Two chronosequences of unsaturated, buried loess sediments, ranging in age from <10,000 years to >1 million years, were investigated to reconstruct patterns of microbial ecological succession that have occurred since sediment burial. The relative importance of microbial transport and survival to succession was inferred from sediment ages, porewater ages, patterns of abundance (measured by direct counts, counts of culturable cells, and total phospholipid fatty acids), activities (measured by radiotracer and enzyme assays), and community composition (measured by phospholipid fatty acid patterns and Biolog substrate usage). Core samples were collected at two sites 40 km apart in the Palouse region of eastern Washington State, near the towns of Washtucna and Winona. The Washtucna site was flooded multiple times during the Pleistocene by glacial outburst floods; the Winona site elevation is above flood stage. Sediments at the Washtucna site were collected from near surface to 14.9 m depth, where the sediment age was approximately 250 ka and the porewater age was 3700 years; sample intervals at the Winona site ranged from near surface to 38 m (sediment age: approximately 1 Ma; porewater age: 1200 years). Microbial abundance and activities declined with depth at both sites; however, even the deepest, oldest sediments showed evidence of viable microorganisms. Same-age sediments had equal quantities of microorganisms, but different community types. Differences in community makeup between the two sites can be attributed to differences in groundwater recharge and paleoflooding. Estimates of the microbial community age can be constrained by porewater and sediment ages. In the shallower sediments (<9 m at Washtucna, <12 m at Winona), the microbial communities are likely similar in age to the groundwater; thus, microbial succession has been influenced by recent transport of microorganisms from the surface. In the deeper sediments, the populations may be considerably older than the porewater ages, since microbial transport is severely restricted in unsaturated sediments. This is particularly true at the Winona site, which was never flooded. 相似文献
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A comparison of two methods for constructing evolutionary distances from a weighted contribution of transition and transversion differences 总被引:3,自引:3,他引:0
Since the initial work of Jukes and Cantor (1969), a number of procedures
have been developed to estimate the expected number of nucleotide
substitutions corresponding to a given observed level of nucleotide
differentiation assuming particular evolutionary models. Unlike the
proportion of different sites, the expected number of substitutions that
would have occurred grows linearly with time and therefore has had great
appeal as an evolutionary distance. Recently, however, a number of authors
have tried to develop improved statistical approaches for generating and
evaluating evolutionary distances (Schoniger and von Haeseler 1993;
Goldstein and Polock 1994; Tajima and Takezaki 1994). These studies clearly
show that the estimated number of nucleotide substitutions is generally not
the best estimator for use in reconstruction of phylogenetic relationships.
The reason for this is that there is often a large error associated with
the estimation of this number. Therefore, even though its expectation is
correct (i.e., on average the expected number of substitutions is
proportional to time- -but see Tajima 1993), it is not expected to be as
useful as estimators designed to have a lower variance.
相似文献
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Paul D. Gottlieb Ann Marshak-Rothstein Karen Auditore-Hargreaves Dorothy B. Berkoben Deborah A. August Roger M. Rosche James D. Benedetto 《Immunogenetics》1980,10(5):545-555
Hybridomas producing mouse monoclonal IgM antibodies specific for Lyt-2.2 and Lyt-3.1 T-cell surface alloantigens have been constructed. Cytotoxic titers of ascites fluids were found to be 10–6 or greater and no lysis of thymocytes of congenic strains bearing the alternative allele was observed at the lowest dilutions tested (12). The anti-Lyt-2.2 monoclonal antibody (HO-2.2) specifically precipiated from extracts of Lyt-2.2-positive thymocytes molecular species indistinguishable from those precipitated by conventional anti-Lyt-2.2 sera. However, by immunoprecipitation criteria (though not by cytotoxicity), the anti-Lyt-3.1 antibody (HO-3.1) demonstrated some cross-reactivity with similar molecular species from Lyt-3.1-negative thymocytes.In addition, three new strains of mice differing from existing strains in the region of theLyt-2 and4Lyt-3 loci have been constructed. They are: C.C58-Lyt-2a, Lyt-3a and C.AKR-Lyt-2a, Lyt-3a, congenic with Balb/cAn and bearingLyt-2
a
andLyt-3
a
alleles of C58/J and AKR/J, respectively; and AKR.C-Lyt-2b, Lyt-3b, congenic with AKR/J and bearing theLyt-2
b
andLyt-3
b
alleles of Balb/cJ.Abbreviations used in this paper DMSO
dimethylsulfoxide
- NP40
Nonidet P-40 detergent
- SaCI
Staphylococcus aureus, Cowan I strain
- SDS
sodium dodecyl sulfate
- PAGE
polyacrylamide gel electrophoreses
- NP-NET buffer
0.15 M NaCl, 0.005 M EDTA, 0.05 M Tris, 0.02% sodium azide, pH 7.4, containing 0.5% or 0.05% NP40 as stated in text 相似文献
16.
gamma-aminobutyric acid increases the water accessibility of M3 membrane-spanning segment residues in gamma-aminobutyric acid type A receptors 总被引:3,自引:0,他引:3 下载免费PDF全文
gamma-Aminobutyric acid type A (GABA(A)) receptors are members of the ligand-gated ion channel gene superfamily. Using the substituted cysteine accessibility method, we investigated whether residues in the alpha(1)M3 membrane-spanning segment are water-accessible. Cysteine was substituted, one at a time, for each M3 residue from alpha(1)Ala(291) to alpha(1)Val(307). The ability of these mutants to react with the water-soluble, sulfhydryl-specific reagent pCMBS(-) was assayed electrophysiologically. Cysteines substituted for alpha(1)Ala(291) and alpha(1)Tyr(294) reacted with pCMBS(-) applied both in the presence and in the absence of GABA. Cysteines substituted for alpha(1)Phe(298), alpha(1)Ala(300), alpha(1)Leu(301), and alpha(1)Glu(303) only reacted with pCMBS(-) applied in the presence of GABA. We infer that the pCMBS(-) reactive residues are on the water-accessible surface of the protein and that GABA induces a conformational change that increases the water accessibility of the four M3 residues, possibly by inducing the formation of water-filled crevices that extend into the interior of the protein. Others have shown that mutations of alpha(1)Ala(291), a water-accessible residue, alter volatile anesthetic and ethanol potentiation of GABA-induced currents. Water-filled crevices penetrating into the interior of the membrane-spanning domain may allow anesthetics and alcohol to reach their binding sites and thus may have implications for the mechanisms of action of these agents. 相似文献
17.
BACKGROUND: By 2016, the proportion of Canadians older than 65 years of age will increase to 16%, and there will be an increase in the absolute number of cases of cardiovascular disease in older Canadians. The Canadian Heart Health Surveys database provides information about this population upon which health policy related to cardiovascular disease can be based. This paper presents for the first time population-based data on the risk factors for cardiovascular disease in older Canadians. METHODS: Canadians from all 10 provinces participated in surveys of cardiovascular risk factors; health insurance registries were used as sampling frames. In each province, probability samples of 2200 adults 18 to 74 years old not living in institutions, on reserves or in military camps were asked to participate in interviews and to undergo testing at clinics for major risk factors for cardiovascular disease. RESULTS: A total of 2739 men (response rate 70%) and 2617 women (response rate 66%) aged 55 to 74 years participated in the survey and also provided follow-up clinical measurements at the clinic. Overall, 52% of participants were hypertensive, 26% had isolated systolic hypertension, and 30% had a total blood cholesterol level of 6.2 mmol/L or greater. Rates of current smoking were lower in women than men (17% v. 22%). Overall, 87% of men and 78% of women who were current smokers smoked at least 10 cigarettes per day. Only slightly more than half of participants exercised at least once a week for at least 15 minutes, and almost half had a body mass index of 27 or greater. In only 4% was no major risk factor for cardiovascular disease detected. INTERPRETATION: Significant numbers of older Canadians have one or more major risk factors for cardiovascular disease. Many of these risk factors are amenable to modification. 相似文献
18.
A J Brown M Berkoben C Ritter N Kubodera Y Nishii E Slatopolsky 《Biochemical and biophysical research communications》1992,189(2):759-764
Catabolism of 22-oxacalcitriol (OCT) in parathyroid cells was compared to that of the parent hormone, 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Catabolism of both compounds was greatly accelerated by pretreatment of the cells with 1,25-(OH)2D3 or OCT. The rate of degradation of OCT was slightly greater than that of 1,25-(OH)2D3. Excess unlabeled OCT or 1,25-(OH)2D3 inhibited metabolism of both tritiated substrates. Ketoconazole, a cytochrome P450 inhibitor, blocked catabolism of both compounds. The major OCT metabolite appeared to be 1,20-dihydroxy-22,23,24,25,26,27-hexanor-vitamin D3 which was not active in suppressing PTH secretion. We conclude that OCT appears to be metabolized by the same vitamin D-inducible side chain oxidation pathway that catabolizes other vitamin D compounds and that its higher than expected suppression of PTH secretion is not due to slower cellular metabolism. 相似文献
19.
Phylogenetic relationships of bolitoglossine salamanders: a demonstration of the effects of combining morphological and molecular data sets 总被引:2,自引:0,他引:2
We analyzed sequence data for 555 bp of the mitochondrial gene cytochrome b
in plethodontid salamanders, taken from 18 ingroup (tribe Bolitoglossini)
and 4 outgroup (tribe Plethodontini) taxa. There were 257 variable sites,
of which 219 were phylogenetically informative. Sequence differences among
taxa exceeded 20%, and there were up to 15% amino acid differences among
the sequences. We also analyzed 37 morphological (including karyological)
characters, taken from the literature. Data were analyzed separately and
then combined using parsimony and likelihood approaches. There is little
conflict between the morphological and DNA data, and that which occurs is
at nodes that are weakly supported by one or both of the data sets. Treated
separately, the morphological and DNA data provide strong support for some
nodes but not for others. The combined data act synergistically so that
good support is obtained for nearly all of the nodes in the tree. Recent
divergences are supported by silent transitions, and older divergences are
supported by a combination of morphological, karyological, DNA
transversion, and amino acid changes. Eliminating silent changes from the
DNA data improves the consistency index and improves some bootstrap and
decay index values for several deeper branches in the tree. However, the
combined data set with all characters included provides a better supported
tree overall. Maximum likelihood and parsimony with all of the data give
not only the same topology but also remarkably similar branch lengths.
Results of this analysis support the monopoly of the supergenera
Hydromantes and Batrachoseps, and of a sister group relationship of
Batrachoseps and the supergenus Bolitoglossa (represented in this study one
species of the genus Bolitoglossa).
相似文献
20.
William J Holmes Richard AJ Darby Martin DB Wilks Rodney Smith Roslyn M Bill 《Microbial cell factories》2009,8(1):35-14