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81.
Seasonal occurrence of Campylobacter spp. in surface waters and their correlation with standard indicator bacteria. 下载免费PDF全文
Campylobacter jejuni, Campylobacter coli, and a Campylobacter-like organism were isolated from a number of natural water sources in central Washington, including ponds, lakes, and small mountain streams at elevations ranging from 1,460 to 5,400 feet (ca. 445 to 1,646 m) above sea level. At the two sites where extensive sampling was done, the bacteria were recovered throughout the year. Generally, the recovery rates were highest in the fall and winter months and lowest during the spring and summer months. Campylobacter density did not show significant correlation with microbiological (plate counts of fecal and total coliforms, fecal streptococci, and heterotrophic bacteria) or physical (water temperature, pH, and conductivity) parameters. 相似文献
82.
Amylase synthesis by the yeasts Saccharomycopsis fibuligera and Schwanniomyces castellii and alluvius is repressed by glucose. Steady state continuous culture data for amylase activity, E, biomass concentration, X, and reducing sugar concentration, S, were fitted to the three-parameter catabolite repression model \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{E}{X} = \frac{{[1 + a(S/X)]}}{{[1 + b(S/X)]}}, $\end{document} and biomass productivity, DX, and amylase productivity, DE, were determined for S. castellii and S. alluvius. 相似文献
83.
Roger L. Williams 《Brittonia》1987,39(2):149-158
George E. Osterhout, an amateur botanist, collected mainly in Colorado between 1893 and 1936. A brief account of his career and character; a list of his proposed new species and new combinations; and his bibliography. 相似文献
84.
85.
In swine, the nasal turbinate epithelium is both a site of swine herpesvirus 1 (pseudorabies virus, PRV) replication and a tissue affected by toxin fromPasteurella multocida serogroup D. We examined the effects of exposure to PRV and exposure to toxin in mice, swine, and nasal turbinate cell cultures. Increased mortality in mice was observed when nonlethal doses of PRV (1000 or 100 plaque-forming units, PFU) were administered along with nonlethal doses (60–200 ng/kg) of toxin. In swine, clinical disease and death in adult pigs was observed after an intradermal injection of toxin (20 ng/kg) and intranasal exposure to 1000 PFU/kg of PRV. Nasal turbinate cell cultures incubated with toxin and PRV had increased protein synthesis, DNA synthesis, and increased recovery of virus particles. These findings indicate that a toxin fromP. multocida serogroup D enhances swine herpesvirus 1 replication and lethality in cell cultures and animal models. 相似文献
86.
87.
Summary Detailed growth analysis in conjunction with information on leaf display and nitrogen uptake was used to interpret competition between Abutilon theophrasti, a C3 annual, and Amaranthus retroflexus, a C4 annual, under ambient (350 l l-1) and two levels of elevated (500 and 700 l l-1) CO2. Plants were grown both individually and in competition with each other. Competition caused a reduction in growth in both species, but for different reasons. In Abutilon, decreases in leaf area ratio (LAR) were responsible, whereas decreased unit leaf rate (ULR) was involved in the case of Amaranthus. Mean canopy height was lower in Amaranthus than Abutilon which may explain the low ULR of Amaranthus in competition. The decrease in LAR of Abutilon was associated with an increase in root/shoot ratio implying that Abutilon was limited by competition for below ground resources. The root/shoot ratio of Amaranthus actually decreased with competition, and Amaranthus had a much higher rate of nitrogen uptake per unit of root than did Abutilon. These latter results suggest that Amaranthus was better able to compete for below ground resources than Abutilon. Although the growth of both species was reduced by competition, generally speaking, the growth of Amaranthus was reduced to a greater extent than that of Abutilon. Regression analysis suggests that the success of Abutilon in competition was due to its larger starting capital (seed size) which gave it an early advantage over Amaranthus. Elevated CO2 had a positive effect upon biomass in Amaranthus, and to a lesser extent, Abutilon. These effects were limited to the early part of the experiment in the case of the individually grown plants, however. Only Amaranthus exhibited a significant increase in relative growth rate (RGR). In spite of the transitory effect of CO2 upon size in individually grown plants, level of CO2 did effect final biomass of competitively grown plants. Abutilon grown in competition with Amaranthus had a greater final biomass than Amaranthus at ambient CO2 levels, but this difference disappeared to a large extent at elevated CO2. The high RGR of Amaranthus at elevated CO2 levels allowed it to overcome the difference in initial size between the two species.This study was supported by a grant from the US Department of Energy 相似文献
88.
J H Hendry C S Potten A Ghafoor J V Moore S A Roberts P C Williams 《Radiation research》1989,118(2):364-374
An exteriorized loop of mouse intestine was exposed to 147Pm low-energy electrons, where the dose rate decreased by a factor of 5 from the base of the crypt to the top of the proliferative zone. A crypt survival curve was obtained, expressed in terms of exposure time. The shape of the curve was interpreted in terms of survival parameters for colony-forming cells (clonogens) derived using 137Cs gamma rays and the depth-dose curve measured for 147Pm electrons. It is concluded that the shape of the crypt survival curve using 147Pm electrons is inconsistent with the notion of either the presence of a large number of clonogens or a small number near the top of the proliferative zone. A computer fitting procedure showed that the best agreement between predicted and observed curves was achieved with 2.7 +/- 0.5 clonogens at cell position 5.6 +/- 0.6, in the putative stem-cell zone. 相似文献
89.
Endothelioma cells expressing the polyoma middle T oncogene induce hemangiomas by host cell recruitment 总被引:25,自引:0,他引:25
Mouse endothelioma cells expressing the polyoma middle T oncogene induced hemangiomas in a variety of species such as mice, rats, chicks, and quails. In embryos and newborn mice the hemangiomas expanded within 10-18 hr of injection, disrupting the vasculature and causing the death of the animal. In contrast, the hemangiomas formed a stable structure reminiscent of benign human hemangiomas in adult mice within 5 days. Analysis of the cells comprising the hemangioma revealed that over 95% of the endothelial cells were host derived. No induction of host cell proliferation was detected, and no endothelial mitogens were secreted by the endothelioma cells in vitro. The maintenance of the hemangioma appeared to require the continuous presence of endothelioma cells. The results indicate that these endothelioma cells act as a potent stimulating agent in the rapid formation of hemangiomas by recruiting nonproliferating host endothelial cells. 相似文献
90.