排序方式: 共有75条查询结果,搜索用时 609 毫秒
61.
Igor Y Oshkin David AC Beck Andrew E Lamb Veronika Tchesnokova Gabrielle Benuska Tami L McTaggart Marina G Kalyuzhnaya Svetlana N Dedysh Mary E Lidstrom Ludmila Chistoserdova 《The ISME journal》2015,9(5):1119-1129
We report observations on the dynamics of bacterial communities in response to methane stimulus in laboratory microcosm incubations prepared with lake sediment samples. We first measured taxonomic compositions of long-term enrichment cultures and determined that, although dominated by Methylococcaceae types, these cultures also contained accompanying types belonging to a limited number of bacterial taxa, methylotrophs and non-methylotrophs. We then followed the short-term community dynamics, in two oxygen tension regimens (150 μM and 15 μM), observing rapid loss of species diversity. In all microcosms, a single type of Methylobacter represented the major methane-oxidizing partner. The accompanying members of the communities revealed different trajectories in response to different oxygen tensions, with Methylotenera species being the early responders to methane stimulus under both conditions. The communities in both conditions were convergent in terms of their assemblage, suggesting selection for specific taxa. Our results support prior observations from metagenomics on distribution of carbon from methane among diverse bacterial populations and further suggest that communities are likely responsible for methane cycling, rather than a single type of microbe. 相似文献
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Comparison of the effects of concentration, pH and anion species on astringency and sourness of organic acids 总被引:4,自引:1,他引:3
The separate effects of concentration, pH and anion species on intensity of
sourness and astringency of organic acids were evaluated. Judges rated
sourness and astringency intensity of lactic, malic, tartaric and citric
acid solutions at three levels of constant pH varying in normality and at
three levels of constant concentration varying in pH. To assess the
comparative sourness and astringency of the organic acid anions of study,
binary acid solutions matched in pH and titratable acidity were also rated.
As pH was decreased in equinormal solutions, both sourness and astringency
increased significantly (P < 0.001). By contrast, as the normality of
the equi-pH solutions was increased, only sourness demonstrated significant
increases (P < 0.001) while astringency remained constant or decreased
slightly. At the lowest normality tested, all solutions were more
astringent than sour (P < 0.05). Although lactic acid was found to be
significantly more sour than citric acid (P < 0.05), no other sourness
or astringency differences among the organic acid anions were noted. This
study demonstrates for the first time that astringency elicited by acids is
a function of pH and not concentration or anion species, and confirms that
sourness is independently influenced by concentration, pH and anion species
of the acid.
相似文献
65.
Patterns of ribosomal RNA evolution in salamanders 总被引:4,自引:0,他引:4
Sequence comparisons are presented for four segments of the large subunit
of ribosomal RNA, including divergent domains D7a and D7b, portions of the
large divergent domains D2, D3, and D8, and evolutionarily conservative
sequences flanking divergent domains. These results resolve phylogenetic
relationships among exemplars of seven families of salamanders and the
three amphibian orders. Phylogenetic analysis confirms the prediction that
divergent domains feature the highest relative rates of base substitution
and length variation within the ribosome, but the divergent domains evolve
more slowly than nuclear noncoding DNA and the silent sites of structural
genes. Base substitutions demonstrate approximately twice as many
transitions as transversions and an uneven distribution among sites within
the divergent domains but no apparent bias in base composition. Length
mutations are primarily small insertions and deletions, with deletions
predominating. The divergent domains appear to be a good source of
phylogenetic information for evolutionary events occurring approximately
100-200 million years ago.
相似文献
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Willeke MC van Roon-Mom Barry A Pepers Peter AC 't Hoen Carola ACM Verwijmeren Johan T den Dunnen Josephine C Dorsman GertJan B van Ommen 《BMC molecular biology》2008,9(1):84
Background
Huntington's disease is a progressive autosomal dominant neurodegenerative disorder that is caused by a CAG repeat expansion in the HD or Huntington's disease gene. Although micro array studies on patient and animal tissue provide valuable information, the primary effect of mutant huntingtin will inevitably be masked by secondary processes in advanced stages of the disease. Thus, cell models are instrumental to study early, direct effects of mutant huntingtin. mRNA changes were studied in an inducible PC12 model of Huntington's disease, before and after aggregates became visible, to identify groups of genes that could play a role in the early pathology of Huntington's disease. 相似文献68.
69.
C Melzer AC Borges F Knebel WS Richter W Combs G Baumann H Theres 《Cardiovascular ultrasound》2004,2(1):1-7
Background
Power Doppler (PD) has improved diagnostic capabilities of vascular sonography, mainly because it is independent from the angle of insonation. We evaluated this technique in a prospective comparison with conventional imaging, consisting in Duplex and Color Doppler, for the evaluation of Renal Artery (RA) stenosis.Methods
Sensitivity, specificity and predictive values of PD and conventional imaging were assessed in a blinded fashion on eighteen patients, 9 with angiographic evidence of unilateral RA stenosis (hypertensive patients) and 9 with angiographically normal arteries (control group). PD images were interpreted with an angiography-like criteria.Results
In the control group both techniques allowed correct visualization of 16 out of the 18 normal arteries (93% specificity). Only in five hypertensive patients RA stenosis was correctly identified with conventional technique (56% sensitivity and 86% negative predictive value); PD was successful in all hypertensive patients (100% sensitivity and negative predictive value), since the operators could obtain in each case of RA stenosis a sharp color signal of the whole vessel with a clear "minus" at the point of narrowing of the lumen. All results were statistically significant (p < 0.01).Conclusions
This study demonstrates that PD is superior to conventional imaging, in terms of sensitivity and specificity, for the diagnosis of RA stenosis, because it allows a clear visualization of the whole stenotic vascular lumen. Especially if it is used in concert with the other sonographic techniques, PD can enable a more accurate imaging of renovascular disease with results that seem comparable to selective angiography. 相似文献70.
Salima FE van Weely J Christiaan van Denderen Martijn PM Steultjens Marike van der Leeden Michael T Nurmohamed Joost Dekker Ben AC Dijkmans Irene E van der Horst-Bruinsma 《Arthritis research & therapy》2012,14(2):R52-6