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11.
Hrvoje Petkovi John Cullum Daslav Hranueli Iain S. Hunter Nataa Peri-Concha Jasenka Pigac Arinthip Thamchaipenet Duica Vujaklija Paul F. Long 《Microbiological reviews》2006,70(3):704-728
From a genetic standpoint, Streptomyces rimosus is arguably the best-characterized industrial streptomycete as the producer of oxytetracycline and other tetracycline antibiotics. Although resistance to these antibiotics has reduced their clinical use in recent years, tetracyclines have an increasing role in the treatment of emerging infections and noninfective diseases. Procedures for in vivo and in vitro genetic manipulations in S. rimosus have been developed since the 1950s and applied to study the genetic instability of S. rimosus strains and for the molecular cloning and characterization of genes involved in oxytetracycline biosynthesis. Recent advances in the methodology of genome sequencing bring the realistic prospect of obtaining the genome sequence of S. rimosus in the near term. 相似文献
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Summary A mutant of Streptomyces coelicolor A3(2) highly resistant to chloramphenicol was selected. It had amplified some chromosomal DNA fragments to a copy number of 20–50. Some of the amplified fragments were cloned and used as hybridisation probes to investigate the spontaneous chloramphenicol-sensitive mutants which occur at high frequency in this species and the closely related species Streptomyces lividans 66. These investigations demonstrated that chloramphenicol sensitivity in both species is associated with large deletions that are at least 40 kb in length. 相似文献
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In an affluent city with many pediatricians a 20% increase in patients seen in a hospital-based walk-in clinic in 1982 prompted a study to determine the characteristics of clinic users and their reasons for using the clinic. It was found that users of the clinic were middle-class, that they had a higher employment rate than the average for the region, and that in 54% of the families both parents worked outside the home. The children of 85% of the families were patients of pediatricians in private practice; most of the others were patients of a family physician in private practice. Most of the children seen at the clinic had had symptoms for more than 24 hours, but few parents had attempted to contact their own physicians. In the previous 12 months 95% of the children had been seen at the clinic, 43% in the month preceding the study. They came to the clinic for two main reasons: the broad range of services offered --laboratory, radiology and pharmacy as well as medical--and the convenient hours, with 71% coming outside of their physicians'' office hours. Given the reality of social trends pediatricians will either have to share their patients with facilities that offer services outside of regular office hours or devise another system for the treatment of their patients. 相似文献
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Cullum AJ 《The American naturalist》1997,150(1):24-47
Many asexual animal species are of hybrid origin, with consequent high levels of heterozygosity. Data from some studies suggest that increased heterozygosity may be functionally correlated with superior performance in a variety of fitness-related traits. Thus, hybrid asexual species could be expected to exhibit some degree of heterosis. This spontaneous heterosis hypothesis is tested in a comparative study of asexual and sexual species of the lizard genus Cnemidophorus. Asexual species of the genus are parthenogenetically reproducing hybrids of the sexual species and as a result have high levels of heterozygosity that have persisted since their origins. Five whole-organism physiological traits (burst speed, endurance, maximal exertion, standard metabolic rate, and evaporative water loss rate) were examined in five asexual species and the sexual species that gave rise to them. Trait values for sexual and asexual species were compared using a nonphylogenetic approach and two phylogenetically controlled approaches capable of dealing with reticulate phylogenies. In contrast to the predictions of the heterosis hypothesis, performance for four of the traits in asexual Cnemidophorus was not statistically different than that in their sexual parental species, and asexuals had significantly worse endurance. On the whole, the overall trend appeared to be toward worse performance in asexuals. An obvious interpretation of these results is that heterozygosity and "vigor" need not be functionally related. However, other factors may be counterbalancing possible beneficial effects of heterozygosity, including detrimental epistatic effects resulting from the karyotypically mixed genome of these hybrids, and the accumulation of deleterious mutations in the asexual lineages via Muller's ratchet. 相似文献
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Alistair J. Cullum Albert F. Bennett Richard E. Lenski 《Evolution; international journal of organic evolution》2001,55(11):2194-2202
Abstract Stressful environments may be considered as those that reduce fitness, sometimes due in part to the increased metabolic expenditure required to sustain life. Direct adaptation to a stressor is expected to increase fitness and reduce maintenance metabolism, with the latter leading to increased biomass production. In this study, we test the general hypothesis that such adaptation to one stressor can preadapt organisms to novel stressful environments. Six lines of Escherichia coli propagated for 2000 generations at 41–42°C (42 group), a stressful temperature, were compared to six control lines propagated for 2000 generations at 37°C (37 group) and to the common ancestor of both groups. We assayed biovolume yield (a measure of growth efficiency) and competitive fitness in the 42 group's selective high temperature environment as well as five novel stressful environments–acid, alkali, ethanol, high osmolarity and peroxide. As previously reported, at high temperature the 42 group had both higher yield and fitness than the 37 group and ancestor. In the novel environments, the 42 group generally produced yields higher than the 37 group (and marginally higher than the ancestor), but we found no differences in competitive fitness among the 37 and 42 groups and the ancestor. We also found that the performance of lines within groups was not correlated across stressful environments for either yield or relative fitness. Because previous adaptation to one stressor did not improve our measure of Darwinian fitness in novel stressful environments, we conclude that the 42 group shows no useful preadaptation, or cross‐tolerance, to these types of environments. 相似文献
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P. A. Cullum M. Bewick Keith Shilkin D. E. H. Tee P. Ayliffe D. C. S. Hutchison J. W. Laws S. A. Mason Lynne Reid P. Hugh-Jones A. M. Macarthur 《BMJ (Clinical research ed.)》1972,2(5805):71-74
In distinguishing between infection and rejection after human lung transplantation clinical and radiological features were unhelpful, and even confusing. However, incipient rejection could be predicted and distinguished from infection by monitoring alterations in lymphocyte activity by the rosette inhibition test. Earlier prediction seems possible by detecting circulating lung-binding antibody. The ability to detect changes in the immunological status of a patient, even before clinical deterioration, has fundamental implications for the management of patients after transplantation. 相似文献
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