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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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Preventing photochemistry in culture media by long-pass light filters alters growth of cultured tissues 总被引:18,自引:4,他引:14 下载免费PDF全文
Exposure of plant tissue culture media to light from fluorescent bulbs changed the growth regulating properties of the media. The light caused nutrient medium-dependent photosensitized degradation of the phytohormone indole-3-acetic acid and other media components. Photochemical changes in culture media were caused by light from 290 to 450 nanometers and were prevented with a yellow long-pass filter. The use of appropriately filtered light when culturing plant material can eliminate unnecessary variability by stabilizing the culture media composition. 相似文献
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Genes essential for the production of a linear, bacterial (1-->3)-beta-
glucan, curdlan, have been cloned for the first time from Agrobacterium sp.
ATCC31749. The genes occurred in two, nonoverlapping, genomic fragments
that complemented different sets of curdlan( crd )-deficient
transposon-insertion mutations. These were detected as colonies that failed
to stain with aniline blue, a (1-->3)-beta-glucan specific dye. One
fragment carried a biosynthetic gene cluster (locus I) containing the
putative curdlan synthase gene, crdS, and at least two other crd genes. The
second fragment may contain only a single crd gene (locus II).
Determination of the DNA sequence adjacent to several locus I mutations
revealed homology to known sequences only in the cases of crdS mutations.
Complete sequencing of the 1623 bp crdS gene revealed highest similarities
between the predicted CrdS protein (540 amino acids) and glycosyl
transferases with repetitive action patterns. These include bacterial
cellulose synthases (and their homologs), which form
(1-->4)-beta-glucans. No similarity was detected with putative
(1-->3)- beta-glucan synthases from yeasts and filamentous fungi.
Whatever the determinants of the linkage specificity of these beta-glucan
synthases might be, these results raise the possibility that
(1-->3)-beta-glucans and (1-->4)-beta-glucans are formed by related
catalytic polypeptides.
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Hong Zhao Jinmin Zhu Kemi Cui Xiaoyin Xu Megan O'Brien Kelvin K Wong Santosh Kesari Weiming Xia Stephen TC Wong 《Cancer cell international》2009,9(1):15
Background
Cancer and Alzheimer's disease (AD) are two seemingly distinct diseases and rarely occur simultaneously in patients. To explore molecular determinants differentiating pathogenic routes towards AD or cancer, we investigate the role of amyloid β protein (Aβ) on multiple tumor cell lines that are stably expressing luciferase (human glioblastoma U87; human breast adenocarcinoma MDA-MB231; and mouse melanoma B16F). 相似文献29.
Tobamoviruses, mostly isolated from solanaceous plants, may represent
ancient virus lineages that have codiverged with their hosts. Recently
completed nucleotide sequences of six nonsolanaceous tobamoviruses allowed
assessment of the codivergence hypothesis and support a third subgroup
within tobamoviruses. The genomic sequences of 12 tobamoviruses and the
partial sequences of 11 others have been analyzed. Comparisons of the
predicted protein sequences revealed three clusters of tobamoviruses,
corresponding to those infecting solanaceous species (subgroup 1), those
infecting cucurbits and legumes (subgroup 2), and those infecting
crucifers. The orchid-infecting odontoglossum ringspot tobamovirus was
associated with subgroup 1 genomes by its coat and movement protein
sequences, but with the crucifer-pathogenic tobamoviruses by the remainder
of its genome, suggesting that it is the progeny of a recombinant. For four
of five genomic regions, subgroup 1 and 3 genomes were equidistant from a
subgroup 2 genome chosen for comparison, suggesting uniform rates of
evolution. A phylogenetic tree of plant families based on the tobamoviruses
they harbor was congruent with that based on rubisco sequences but had a
different root, suggesting that codivergence was tempered by rare events of
viruses of one family colonizing another family. The proposed subgroup 3
viruses probably have an origin of virion assembly in the movement protein
gene, a large (25-codon) overlap of movement and coat protein open reading
frames, and a comparably shorter genome. Codon-position- dependent base
compositions and codon prevalences suggested that the coat protein frame of
the overlap region was ancestral. Bootstrapped parsimony analysis of the
nucleotides in the overlap region and of the sequences translated from the
-1 frame (the subgroup 3 movement protein frame) of this region produced
trees inconsistent with those deduced from other regions. The results are
consistent with a model in which a no or short overlap organization was
ancestral. Despite encoding of subgroup 2 and 3 movement protein C-termini
by nonhomologous nucleotides, weak similarities between their amino acid
sequences suggested convergent sequence evolution.
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Gang Li Tianming Liu Ashley Tarokh Jingxin Nie Lei Guo Andrew Mara Scott Holley Stephen TC Wong 《BMC cell biology》2007,8(1):40