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1.
A phosphotransferase-dependent aryl-β-glucoside uptake and utilisation system (abg) was isolated from the ruminal Clostridium (“C. longisporum”). The system is composed of three genes, abgG, abgF and abgA, and a number of regulatory regions, including terminator/antiterminator type stem-loop structures preceding the abgG and abgF genes. Similarity analysis of the proteins encoded by these genes indicated that they were responsible for the regulation of the abg system through antitermination (AbgG), the uptake and phosphorylation of aryl-β-glucosides (AbgF) and the hydrolysis of the intracellular phosphorylated glycosides (AbgA). Experimental evidence for the functions of AbgF and AbgA was obtained. Although it was not possible to demonstrate any function for AbgG, a promoter 5′ to the abgG gene was identified which was responsible for expression of the downstream genes. The abg system is remarkably similar to operons from the gram negative Enterobacteriaceae, both in the coding and non-coding regulatory regions. Received: 3 April 1997 / Accepted: 8 September 1997  相似文献   
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Speakman and co-workers suggested the diurnal Samoan flying fox, Pteropus samoensis, may be at risk of hyperthermia when flying during the day, particularly at high levels of insolation. We monitored activity of this bat and climate simultaneously at two different sites and four times of year in American Samoa. Flight activity varied significantly with time of day, between days, study sites and seasons. Out of the six data sets collected, the four with the highest mean levels of insolation showed a significant decrease in bat numbers with increasing temperature and sunlight. When each individual activity count was directly compared to the predictions of Speakman and co-workers'' biophysical model, 85 to 95% of bat flight activity was found to be in conditions the model suggested would not pose a risk of hyperthermia. This supports the suggestion that in extreme conditions the animals would not fly as they risked overheating. The 5 to 15% of counts in which animals were seen to fly in conditions the model predicted they should not may be explained by erroneous assumptions underlying the model predictions.  相似文献   
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Abstracts     
William A. R. Thomson 《CMAJ》1955,72(3):234-237
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Opportunities to investigate selection in free-living species during a naturally occurring epidemic are rare; however, we assessed innate immunocompetence in Florida scrub-jays before the population suffered the greatest over-winter mortality in 20 years of study. Propitiously, three months prior to the epidemic, we had sampled a number of male breeders to evaluate a suite of physiological measures that are commonly used to estimate the overall health-state of an individual. There was a significant, positive selection gradient for both Escherichia coli bacterial killing capability and body condition, suggesting that directional selection had occurred upon each of these traits during the disease epidemic.  相似文献   
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Lipids associated with a threat induced epidermal gel secretion from the catfish, Arius thalassinus, have been analyzed. Phospholipids, neutral lipids and glycolipids are all present and each of these subclasses has been analyzed by thin layer and gas chromatography with a general similarity with membrane lipids being noted. The epidermal gel lipids differed from total liver lipids of the catfish. Fatty acid analysis showed the gel lipid to be rich in the unsaturated fatty acids: oleate (omega 7, C18:1), arachidonate (omega 6, C20:4), and docosahexaenoate (omega 3, C22:6). Some prostaglandins were quantitated in lipid extracts from the epidermal gel.  相似文献   
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Brush border membranes (BBM) were isolated from the jejunum and ileum of control, ad libitum (CAL); control, food-restricted (CFR); control, weight gain (CWG); and ethanol-fed (EF) rabbits. Jejunal alkaline phosphatase activity was similar among control groups, but higher in CAL than EF animals. Sucrase activity was higher in EF and CWG animals than in CAL and CFR. The alkaline phosphatase/sucrase ratio was lower in EF than control animals. Ileal enzyme marker activity was similar among EF and control animals. Sucrase (S) activity was lower in the ileum than in the jejunum. Jejunal free fatty acid and phospholipid/cholesterol (PL/C) were lower in EF than control animals, whereas ileal lipid content was generally similar among all animal groups. Total phospholipid content was similar between sites, but the cholesterol and free fatty acid content were lower in the ileum than the jejunum. The phospholipid/cholesterol ratio was increased only in the ileum of EF animals. The amount of lecithin was decreased in the jejunal BBM of EF animals resulting in a decreased choline/amine phospholipid ratio as compared with control animals. The ileal phospholipid composition was similar among all groups. A large increase in villus height is observed in the jejunum of EF animals. Villus surface area and mucosal surface area are altered with ethanol feeding and food deprivation. Thus, (i) there is a gradient of S and cholesterol between the BBM of jejunum and ileum; (ii) changes in food intake are associated with changes in the morphology as well as the enzyme marker and lipid content of BBM.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
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Observed intensification of precipitation extremes, responsible for extensive societal impacts, are widely attributed to anthropogenic sources, which may include indirect effects of agricultural irrigation. However quantifying the effects of irrigation on far-downstream climate remains a challenge. We use three paired Community Earth System Model simulations to assess mechanisms of irrigation-induced precipitation trends and extremes in the conterminous US and the effect on the terrestrial carbon sink. Results suggest precipitation enhancement in the central US reduced drought conditions and increased regional carbon uptake, while further downstream, the heaviest precipitation events were more frequent and intense. Specifically, moisture advection from irrigation in the western U.S. and recycling of enhanced local convective precipitation produced very-heavy storm events that were 11% more intense and occurred 23% more frequently in the densely populated greater New York City region.  相似文献   
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