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An analysis of restriction fragment length polymorphism (RFLP) using eight
residential insertion sequence (IS) elements as hybridization probes
reveals that the genome of resting bacteria is more dynamic than it was
long believed. Escherichia coli strains stored in agar stabs for up to 30
yr accumulate a genetic variation which is correlated to time of storage.
This spontaneous mutagenesis is often IS-specific, with particularly high
activity for IS5, and thus suggests that transpositional DNA rearrangements
are a major cause for the observed genetic polymorphism. The RFLP patterns
indicate a burst of IS30 transposition to occur occasionally. Mutation rate
is estimated by two different methods to roughly 10(-5) IS-related DNA
rearrangements per bacterial chromosome per hour of storage for the eight
IS elements studied. A pedigree derived from the RFLP data reveals that
populations had evolved independently in each stab and showed no signs of
convergence. Relics of an assumed ancestral population were still present
in the stab cultures, but the elder stabs provided mostly mutants. These
results indicate that cells placed under nutritional deprivation might have
a highly plastic genome and suggest that such plasticity might play an
adaptive role.
相似文献
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Sean WM Collins Xisto Martins Andrew Mitchell Awegechew Teshome John T Arnason 《Journal of ethnobiology and ethnomedicine》2007,3(1):1-10
In recent years, diverse scholars have addressed the issue of the chemosensory perceptions associated with traditional medicines, nevertheless there is still a distinct lack of studies grounded in the social sciences and conducted from a cross-cultural, comparative perspective. In this urban ethnobotanical field study, 254 informants belonging to the Gujarati, Kashmiri and English ethnic groups and living in Western Yorkshire in Northern England were interviewed about the relationship between taste and medicinal perceptions of five herbal drugs, which were selected during a preliminary study. The herbal drugs included cinnamon (the dried bark of Cinnamomum verum, Lauraceae), mint (the leaves of Mentha spp., Lamiaceae), garlic (the bulbs of Allium sativum, Alliaceae), ginger (the rhizome of Zingiber officinale, Zingiberaceae), and cloves (the dried flower buds of Syzygium aromaticum, Myrtaceae). The main cross-cultural differences in taste perceptions regarded the perception the perception of the spicy taste of ginger, garlic, and cinnamon, of the bitter taste of ginger, the sweet taste of mint, and of the sour taste of garlic. The part of the study of how the five selected herbal drugs are perceived medicinally showed that TK (Traditional Knowledge) is widespread among Kashmiris, but not so prevalent among the Gujarati and especially the English samples. Among Kashmiris, ginger was frequently considered to be helpful for healing infections and muscular-skeletal and digestive disorders, mint was chosen for healing digestive and respiratory troubles, garlic for blood system disorders, and cinnamon was perceived to be efficacious for infectious diseases. Among the Gujarati and Kashmiri groups there was evidence of a strong link between the bitter and spicy tastes of ginger, garlic, cloves, and cinnamon and their perceived medicinal properties, whereas there was a far less obvious link between the sweet taste of mint and cinnamon and their perceived medicinal properties, although the link did exist among some members of the Gujarati group. Data presented in this study show how that links between taste perceptions and medicinal uses of herbal drugs may be understood as bio-cultural phenomena rooted in human physiology, but also constructed through individual experiences and culture, and that these links can therefore be quite different across diverse cultures. 相似文献
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