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71.
Dielectrophoresis of Cells   总被引:4,自引:1,他引:3       下载免费PDF全文
Dielectrophoresis, the motion produced by the action of nonuniform electric field upon a neutral object, is shown to be a simple and useful technique for the study of cellular organisms. In the present study of yeast (Saccharomyces cerevisiae) using a simple pin-pin electrode system of platinum and high-frequency alternating fields, one observes that the collectability of cells at the electrode tip, i.e. at the region of highest field strength, depends upon physical parameters such as field strength, field uniformity, frequency, cell concentration, suspension conductivity, and time of collection. The yield of cells collected is also observed to depend upon biological factors such as colony age, thermal treatment of the cells, and chemical poisons, but not upon irradiation with ultraviolet light. Several interesting side effect phenomena coincident with nonuniform electric field conditions were observed, including stirring (related to “jet” effects at localized electrode sites), discontinuous repulsions, and cellular rotation which was found to be frequency dependent.  相似文献   
72.
A study was conducted to determine a physicochemical profile of a new deep-storage reservoir and to determine the influence of impoundment and thermal stratification in the reservoir on the physicochemical limnology of the parent river. The presence of thermal stratification from May through November caused the most significant change in water conditions. Of 23 parameters studied, 12 remained unchanged, 10 improved, and 2 deteriorated (Table VI).The greatest downstream changes in water conditions from those upstream from the reservoir were a decrease in temperature, an increase of ammonia, and the presence of hydrogen sulfide during the period of thermal stratification. Ammonia did not increase to a level considered to be toxic to aquatic species. It could, however, serve as a nutrient for certain species of plants and result in a change in community structure.Water tempeature downstream from the reservoir was always within the annual temperature range of the river upstream from the reservoir; however, the summer maximum in the tailrace was decreased to a temperature that could interfere wih the normal life cycle of many species.  相似文献   
73.
74.
The effect of three groups of metabolic inhibitors on the incorporation of Fe and release of bicarbonate from transferrin by rabbit reticulocytes was measured. Inhibitors which affect reticulocyte Fe and transferrin uptake to the same extent (sodium arsenite, N-ethylmaleimide and iodoacetamide); those which inhibit reticulocyte Fe uptake to a greater extent than transferrin uptake (NaN3, NaF, NaCN, rotenone, oligomycin, 2,4-dinitrophenol and cycloheximide); and compounds which after reticulocyte heme synthesis (CoCl2, isonicotinic acid hydrazide and hemin) were used. In each case the effect on Fe incorporation and bicarbonate release was the sameThus, additional evidence has been obtained for the idea that the reticulocyte-mediated release of Fe and bicarbonate from transferrin are tightly coupled. The results are consistent with the hypothesis that an enzymatic attack on transferrin-bound bicarbonate is involved in the removal of Fe from transferrin by erythroid cells.  相似文献   
75.
Summary The variation of X-ray sensitivity was investigated during the cell cycle. The cells were most sensitive during the S phase and less sensitive during the G2- and G1 phase. Furthermore, the repair of X-ray damage was investigated in stationary (plateau phase) cells. The cells of both lines were able to repair damage to nearly the same extent.
Zusammenfassung Die Variation der Strahlensensibilität während des Zellcyclus wurde untersucht. Die Zellen reagierten am sensibelsten in der S-Phase, weniger sensibel in der G2-und G1-Phase. Weiterhin wurde die Reparation von Strahlenschäden bei stationären (Plateauphase-)Zellen untersucht. Die Zellen beider Linien sind in etwa gleichem Maße reparationsfähig.


Supported (I-IV) by the Deutsche Forschungsgemeinschaft (Mi/100, 1-7).  相似文献   
76.
Insofar as saturation kinetics are applicable to the growth of phytoplankton in laboratory experiments and to growth in nature, the computer modeling of intracellular nutrient partitioning in populations of cells can lead to better understanding of the dynamics of natural populations. A three-compartment mathematical model was developed to represent a phytoplankton population having the capability to store nitrogen in a nitrate-limited environment. Parameters were estimated by fitting the model to data from two chemostat experiments reported by Caperon (1968). The model was used to simulate growth dynamics observed in chemostat and batch experiments. The model demonstrated the changes which may occur in the nitrogenous constituents of a phytoplankton population with time and environmental conditions. The model also demonstrates three phenomena which have been observed in field and laboratory experiments but which are not represented by the customary Monod model: (1) uptake rates may significantly exceed not growth rates, (2) high growth rates may be encountered at very low environmental nitrate concentrations, and (3) the ratio of internal nitrogen to population size may change significantly during a study period. It is suggested that the amount of nitorgen in storage may be used as an indicator of the physiological state of a monospecific population. Parameters for the one-compartment Monod model were estimated by customary methods form data generated by the three-compartment model. It was shown that difficulties encountered in estimating the yield coefficient and the decay coefficient may be attributed to the intracellular storage phenomenon. It was also demonstrated that the one-compartment Monod model was inadequate to accurately represent population growth in chemostat experiments when intracellular storage is a significant factor.  相似文献   
77.
Stages in the direct penetration of adenovirus through the cell membrane are illustrated. Phagocytosis with rupture of the vacuole and release of virus into the cytoplasm may also account for entry of some particles. Uncoating by digestion within phagosomes was not observed. Rather, alteration of capsid and core occurred to virions free in the cytoplasm. Nucleoprotein released from virus close to the nucleus was transported to the nuclear matrix by a unique mechanism. These events were not prevented by puromycin and hence were not dependent upon the synthesis of new enzymes. They were, however, energy-dependent.  相似文献   
78.
Studies with alpha-ketoglutarate dehydrogenase mutants of Escherichia coli   总被引:10,自引:0,他引:10  
Summary Two classes of mutant lacking -ketoglutarate dehydrogenase complex activity were detected by biochemical analysis of strains of Escherichia coli requiring succinate for aerobic growth on glucose minimal medium. One class, designated sucA, lacked the -ketoglutarate decarboxylase component (E1) whereas the other class, sucB, lacked the dihydrolipoyl transsuccinylase component (E2). Studies with mixed cell-free extracts showed that the overall dehydrogenase activity could be reconstituted from several pairs of sucA plus sucB mutants but not from mixtures of mutants of the same class. Transduction analysis with phage P1 indicated close linkage between the two genes and their frequencies of cotransduction with gal were similar. The order of the two genes was also established as sucA (E1)-sucB(E2)...gal by reciprocal three-point crosses with several pairs of mutants.  相似文献   
79.
Morphological, cultural, biochemical, and serological characteristics of 79 strains of Vibrio parahemolyticus isolated from patients suffering from gastroenteric disease in Japan were compared with 17 suspected V. parahemolyticus cultures isolated from wound infections and 14 nonpathogenic vibrios isolated from an estuarine environment in the United States. These groups were differentiated on the basis of several key reactions which included: the range of growth temperature and salt tolerance; the production of catalase and acetoin; the hydrolysis of starch; the fermentation and utilization as single carbon source of sucrose, cellobiose, and arabinose; and the ability to swarm on 1% agar. The separation of the groups on the basis of cultural and biochemical analyses was confirmed by means of slide agglutinations with specific anti-K antisera. The results of this study strongly suggest that the wound infection isolates are V. parahemolyticus species which are easily distinguished from the nonpathogenic estuarine vibrios.  相似文献   
80.
Examination of Market Foods for Coliform Organisms   总被引:4,自引:3,他引:1       下载免费PDF全文
Food specimens (490) in nine categories were examined for total aerobic plate count and numbers and types of coliform organisms, including the enteropathogenic Escherichia coli (EEC). The total counts were compared with various suggested standards, and a limit of 100,000/g appeared to be a realistic goal, except for certain food types with a high level of natural flora. Plate counts in VRB were compared to counts obtained by isolation by enrichment in LST Broth, and the latter method produced a higher percentage of isolations. The presence of E. coli was determined by use of EC Medium incubated at 44.5 +/- 0.1 C. Only 40.4% of the positive EC tubes, however, contained E. coli. It appeared that a limit of 10 coliform organisms per g as a suggested standard could be met with several types of foods. Isolation of EEC was obtained only three times, or in 0.6% of the specimens.  相似文献   
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