tailieunhanh - Báo cáo y học: "Evidence of circadian rhythms in nonphotosynthetic bacteria"

Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Wertheim cung cấp cho các bạn kiến thức về ngành y đề tài: Evidence of circadian rhythms in nonphotosynthetic bacteria? | Soriano et al. Journal of Circadian Rhythms 2010 8 8 http content 8 1 8 DEBATE JOURNAL OF CIRCADIAN RHYTHMS Open Access Evidence of circadian rhythms in nonphotosynthetic bacteria María I Soriano Begona Roibás Ana B García Manuel Espinosa-Urgel Abstract Examples of circadian rhythms have been described in eukaryotic organisms and in photosynthetic bacteria but direct proof of their existence in other prokaryotes is limited and has been largely ignored. The aim of this article is to review existing evidence and to present preliminary results that suggest that the heterotrophic bacterium Pseudomonas putida shows regular variations in its growth pattern synchronized with light darkness cycles. We put forward the hypothesis that circadian regulation of certain processes can take place in non-photosynthetic prokaryotes and may represent an adaptative advantage in specific environments. Background Activities and physiological processes taking place with a periodicity of around 24 h have been described in many organisms 1 . Circadian cycles synchronized and entrained by light and darkness cycles determine in mammals the periods of sleep and vigil changes in body temperature or hormone production among other functions. In plants the release of hormones such as ethylene certain developmental processes or the release of seed and root exudates are subject to this periodicity 2 . The absence of circadian cycles is generally assumed for bacteria except in the case of cyanobacteria in which photosynthesis and nitrogen fixation are either spatially segregated in heterocyst-forming bacteria or temporally separated and controlled by circadian periodicity. Both processes would not be possible at the same time in a single cell because oxygen released during photosynthesis inhibits nitrogenase activity. Circadian rhythms in photosynthetic bacteria are being thoroughly studied and the molecular mechanisms that allow the functioning and maintenance of the .

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