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1.
Ambient outdoor concentrations and size distributions of airborne microbial particles were measured approximately weekly for 2 years in a Washington, D.C., suburban area. The study objective was to characterize microbial air quality in the vicinity of a proposed sewage sludge composting facility. During the study, 379 samples were taken at 17 stations, using Andersen microbial samplers. Concentration ranges (in viable particles per cubic meter) were as follows: airborne mesophilic fungi, 0 to 7,220 with a geometric mean of 273; thermophilic fungi, 0 to 193 with a median of 2.1; Aspergillus fumigatus, 0 to 71 with a median of 1.0; aerobic bacteria, 4.2 to 1,640 with a geometric mean of 79; and fecal streptococci, 0 to 5.7 with a median of 0. No fecal coliforms were recovered. The potentially respirable fraction (less than 8 microns) averaged 34% for total bacteria, 56% for mesophilic fungi, 91% for thermophilic fungi, and 95% for A. fumigatus. The specific sampling location was not a major factor affecting microbial particle concentrations or size distributions. Conversely, the time of year was an important determinant of viable particle concentrations for all groups of microorganisms studied. The highest concentrations were observed in summer and fall, with significantly lower levels detected in winter. In general, the microbial data did not correlate with other variables, including weather conditions, measured in this study. 相似文献
2.
A novel experimental method was developed which allows the determination of the threshold concentration of sucrose by use of a linear sucrose gradient in water. With this method a continuous tasting of the test-liquid is possible. A panel of 15 persons experienced in taste-testing was used. Three gradients of different steepness were applied: 0 to 1.5% (w/w) sucrose in 2 min (I), 3 min (II) and 4 min (III). The results of the new method were compared with those of the standard method (DIN). With gradients I and II we found values which were significantly higher than those of the standard method (I: 0.49% (w/w); II: 0.46% (w/w); DIN: 0.31% (w/w)), whereas with gradient III the same threshold value was found as with the DIN-Method (III: 0.32% (w/w)). 相似文献
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A DNA primer/probe system for the rapid and sensitive detection of Mycobacterium tuberculosis-complex pathogens 总被引:1,自引:0,他引:1
N T Ralphs S Garrett R Morse J B Cookson P W Andrew G J Boulnois 《The Journal of applied bacteriology》1991,70(3):221-226
A 1.5 kb EcoRI-BamHI restriction fragment from Mycobacterium tuberculosis was found to hybridize specifically with genomic DNA from M. tuberculosis-complex organisms. Primers were designed from the terminal sequences of this fragment and used to amplify uniquely M. tuberculosis-group DNA in a polymerase chain reaction. It is suggested that a combination of these primers and probe will prove a useful tool for the early diagnosis of tuberculous infections. 相似文献
8.
Stephen Rawsthorne Frank R. Minchin Rodney J. Summerfield Claire Cookson James Coombs 《Phytochemistry》1980,19(3):341-355
The literature concerning the metabolism of carbon compounds during the reduction, assimilation and translocation of nitrogen in root nodules of leguminous plants is reviewed. The reduction of dinitrogen requires an energy source (ATP) and a reluctant which are both supplied by respiratory catabolism of carbohydrates produced by the host plant. Photosynthates are also required to generate the carbon skeletons for amino acid or urcide synthesis during the assimilation of ammonia produced by the bacteria within the nodule tissue. Competition for photosynthates occurs between the bacteroids, nodule tissue and the various vegetative and reproductive sinks in the host plant. The nature of carbon compounds involved in these processes, their routes of metabolism, the mechanisms of control and the partitioning of metabolises between the various sites of utilization are only poorly understood. It is apparent that dinitrogen is reduced to ammonia in the bacteroids. Both fast- and slow-growing strains of Rhizobium possess the Entner-Doudoroff pathway of glucose catabolism, and some, if not all, enzymes of the Emden-Meyerhof pathway. Some bacterial cultures also metabolize carbon through the ketogluconate pathway but only the fast-growing strains of cultured rhizobia possess the key enzyme of the pentose phosphate pathway (6-phosphogluconate dehydrogenase). The host cells are thought to contain the complete Emden-Meyerhof pathway and tricarboxylic acid cycle, which provides the carbon skeletons for assimilation of the ammonia, formed by the bacteroids, into α-amino acids. A pathway of anapleurotic carbon conservation, operative in the host cells, synthesizes oxaloacetic acid through β-carboxylation of phosphoenol pyruvate. This process could be important in the recapture and assimilation of respired CO2 in the rhizosphere. The main route of assimilation of ammonia produced by the bacteroids would appear to be via the glutamine synthetase-glutamate synthase pathway in the host cells. However, glutamate dehydrogenase may also be involved in ammonia assimilation. These enzymes also occur in in vitro cultures of Rhizobium and in bacteroids where they presumably participate in the synthesis of amino acids for growth of the bacteria or bacteroids. Nitrogen assimilated into glutamine or glutamate is exported from the nodules in a variety of forms, which include asparagine, glutamine, aspartate, homoserine and allantoates, in proportions which depend on the legume species. Studies on regulation of the overall process have focussed on expression of bacteroid genes and on the control of enzyme activity, at the level of nitrogenase and enzymes of nitrogen assimilation in particular. However, due to the wide range of experimental techniques, environmental conditions and plant species which have been used, no clear conclusions can yet be drawn. The pathways of carbon flow in nitrogen metabolism, particularly in relation to the synthesis of ureides and the regulation of carbon metabolism, remain key areas for future research in symbiotic nitrogen fixation. 相似文献
9.
The flexibility and self-healing properties of animal cell surface membranes are well known. These properties have been best exploited in various micrurgical studies on living cells (2, 3), especially in amoebae (7, 20). During nuclear transplantation in amoebae, the hole in the membrane through which a nucleus passes can have a diameter of 20-30 μm, and yet such holes are quickly sealed, although some cytoplasm usually escapes during the transfer. While enucleating amoebae in previous studies, we found that if a very small portion of a nucleus was pushed through the membrane and exposed to the external medium, the amoeba expelled such a nucleus on its own accord. When this happened, a new membrane appeared to form around the embedded portion of the nucleus and no visible loss of cytoplasm occurred during nuclear extrusion. In the present study, we examined amoebae that were at different stages of expelling partially exposed nuclei, to follow the sequence of events during the apparent new membrane formation. Unexpectedly, we found that a new membrane is not formed around the nucleus from inside but a hole is sealed primarily by a constriction of the existing membrane, and that cytoplasmic filaments are responsible for the prevention of the loss of cytoplasm. 相似文献
10.
Christopher I Keeling Macaire MS Yuen Nancy Y Liao T Roderick Docking Simon K Chan Greg A Taylor Diana L Palmquist Shaun D Jackman Anh Nguyen Maria Li Hannah Henderson Jasmine K Janes Yongjun Zhao Pawan Pandoh Richard Moore Felix AH Sperling Dezene P W Huber Inanc Birol Steven JM Jones Joerg Bohlmann 《Genome biology》2013,14(3):R27