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Bacterial Community Structure Along Moisture Gradients in the Parafluvial Sediments of Two Ephemeral Desert Streams 总被引:1,自引:0,他引:1
Zeglin LH Dahm CN Barrett JE Gooseff MN Fitpatrick SK Takacs-Vesbach CD 《Microbial ecology》2011,61(3):543-556
Microorganisms inhabiting stream sediments mediate biogeochemical processes of importance to both aquatic and terrestrial
ecosystems. In deserts, the lateral margins of ephemeral stream channels (parafluvial sediments) are dried and rewetted, creating
periodically wet conditions that typically enhance microbial activity. However, the influence of water content on microbial
community composition and diversity in desert stream sediments is unclear. We sampled stream margins along gradients of wet
to dry sediments, measuring geochemistry and bacterial 16S rRNA gene composition, at streams in both a cold (McMurdo Dry Valleys,
Antarctica) and hot (Chihuahuan Desert, New Mexico, USA) desert. Across the gradients, sediment water content spanned a wide
range (1.6–37.9% w/w), and conductivity was highly variable (12.3–1,380 μS cm−2). Bacterial diversity (at 97% sequence similarity) was high and variable, but did not differ significantly between the hot
and cold desert and was not correlated with sediment water content. Instead, conductivity was most strongly related to diversity.
Water content was strongly related to bacterial 16S rRNA gene community composition, though samples were distributed in wet
and dry clusters rather than as assemblages shifting along a gradient. Phylogenetic analyses showed that many taxa from wet
sediments at the hot and cold desert site were related to, respectively, halotolerant Gammaproteobacteria, and one family within the Sphingobacteriales (Bacteroidetes), while dry sediments at both sites contained a high proportion of taxa related to the Acidobacteria. These results suggest that bacterial diversity and composition in desert stream sediments is more strongly affected by hydrology
and conductivity than temperature. 相似文献
34.
Pettersen FO Torheim EA Dahm AE Aaberge IS Lind A Holm M Aandahl EM Sandset PM Taskén K Kvale D 《Journal of virology》2011,85(13):6557-6566
Chronic HIV infection is characterized by chronic immune activation and dysfunctional T cells with elevated intracellular cyclic AMP (cAMP), which inhibits the T cell activation capability. cAMP may be induced by prostaglandin E(2) following lipopolysaccharide (LPS)-induced upregulation of cyclooxygenase type 2 (COX-2) in monocytes due to the elevated LPS levels in patients with chronic HIV infection. This hypothesis was tested using celecoxib, a COX-2 inhibitor, for 12 weeks in HIV-infected patients without antiretroviral treatment in a prospective, open, randomized exploratory trial. Thirty-one patients were randomized in the trial; 27 completed the study, including 13 patients on celecoxib. Celecoxib reduced chronic immune activation in terms of CD38 density on CD8(+) T cells (-24%; P = 0.04), IgA levels (P = 0.04), and a combined score for inflammatory markers (P < 0.05). Celecoxib further reduced the inhibitory surface receptor programmed death 1 (PD-1) on CD8(+) T cells (P = 0.01), including PD-1 on the HIV Gag-specific subset (P = 0.02), enhanced the number of CD3(+) CD4(+) CD25(+) CD127(lo/-) Treg or activated cells (P = 0.02), and improved humoral memory recall responses to a T cell-dependent vaccine (P = 0.04). HIV RNA (P = 0.06) and D dimers (P = 0.07) tended to increase in the controls, whereas interleukin-6 (IL-6) possibly decreased in the treatment arm (P = 0.10). In conclusion, celecoxib downmodulated the immune activation related to clinical progression of chronic HIV infection and improved T cell-dependent functions in vivo. 相似文献
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Nutrient cycling and energy flow in ecosystems are tightly linked through the metabolic processes of organisms. Greater uptake
of inorganic nutrients is expected to be associated with higher rates of metabolism [gross primary production (GPP) and respiration
(R)], due to assimilatory demand of both autotrophs and heterotrophs. However, relationships between uptake and metabolism
should vary with the relative contribution of autochthonous and allochthonous sources of organic matter. To investigate the
relationship between metabolism and nutrient uptake, we used whole-stream and benthic chamber methods to measure rates of
nitrate–nitrogen (NO3–N) uptake and metabolism in four headwater streams chosen to span a range of light availability and therefore differing rates
of GPP and contributions of autochthonous carbon. We coupled whole-stream metabolism with measures of NO3–N uptake conducted repeatedly over the same stream reach during both day and night, as well as incubating benthic sediments
under both light and dark conditions. NO3–N uptake was generally greater in daylight compared to dark conditions, and although day-night differences in whole-stream
uptake were not significant, light–dark differences in benthic chambers were significant at three of the four sites. Estimates
of N demand indicated that assimilation by photoautotrophs could account for the majority of NO3–N uptake at the two sites with relatively open canopies. Contrary to expectations, photoautotrophs contributed substantially
to NO3–N uptake even at the two closed-canopy sites, which had low values of GPP/R and relied heavily on allochthonous carbon to
fuel R. 相似文献
37.
Liane Dahm Fanny Klugmann Angeles Gonzalez-Algaba Bernhard Reuss 《Cell biology and toxicology》2010,26(6):579-591
Gap junctions (GJ) represent a cellular communication system known to influence neuronal differentiation and survival. To
assess a putative role of this system for neural effects of tamoxifen (TAM) and raloxifene (RAL), we used the human teratocarcinoma
cell line NTera2/D1, retinoic acid (RA)-dependent neuronal differentiation of which is regulated by gap junctions formed of
connexin43 (Cx43). As demonstrated by Western blot analysis, concentrations above 1 μmol/l for TAM, and 0.1 μmol/l for RAL
lead to a temporary time- and concentration-dependent increase in Cx43 immunoreactivity, which reached a peak for TAM after
1 day and for RAL after 2 days. Immunocytochemical stainings revealed the increase in Cx43 immunoreactivity to result from
an accumulation in intracellular compartments such as the Golgi apparatus or lysosomes. In addition, TAM and RAL were able
to prevent the RA-dependent decrease of Cx43 immunoreactivity in NTera2/D1 cells, normally observed during neuronal differentiation.
This suggested a suppression of neuronal differentiation to result from these substances. According to this, treatment of
NTera2/D1 cells with 10 μmol/l TAM or RAL during weeks 1 and 2 of a 6 weeks RA-driven differentiation schedule impaired, whereas
treatment during weeks 5 and 6 did not impair, neuronal differentiation of these cells. Modulation of GJ coupling between
NTera2/D1 cells by TAM and RAL seems therefore to perturb early neuronal differentiation, whereas differentiated neurons in
the mature brain seem to be not affected. These effects could be of importance for actions of TAM and RAL on early embryonic
steps of nervous system formation. 相似文献
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Changes in gibberellin-like activity and content of indole type auxins were investigated during grain development of the two high-lysine barley (Hordeum vulgare L.) genotypes Sv 73608 and Risø 1508, and their corresponding normal cultivars Mona and Bomi. A peak in gibberellin-like activity was found in developing grains of the normal cultivars about 18 days after anthesis, whereas the grains of the high-lysine genotypes showed a two to five times higher maximum about 3–4 days later. The auxin content of the cultivar Bomi showed a maximum between the 22nd and the 29th day after anthesis, whereas, throughout their development the grains of the mutant Risø 1508 exhibited only about 1/10 of the maximum level of auxin found in the grains of Bomi. The normal cultivar Mona also displayed higher contents of auxin than the high-lysine genotypes Sv 73608, particularly at the later stages of grain growth, but the differences in concentration were considerable smaller than for the pair ‘Bomi’—‘Risø 1508’. It is suggested that auxins play an important role in the development of barley grains. 相似文献
40.