%0 Journal Article
%T Evidence of circadian rhythms in non-photosynthetic bacteria?
%A Mar¨ªa I Soriano
%A Bego£¿a Roib¨¢s
%A Ana B Garc¨ªa
%A Manuel Espinosa-Urgel
%J Journal of Circadian Rhythms
%D 2010
%I BioMed Central
%R 10.1186/1740-3391-8-8
%X 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 circadian clock are fairly well understood [3]. The clock is composed of three proteins, KaiA, KaiB, and KaiC, which function as a central oscillator through phosphorylation/dephosphorylation cycles. The system is synchronized via a signal input pathway in which sensory proteins are known to transmit light/darkness information to the clock, while a series of clock-controlled regulators transduce the temporal information to downstream processes. Expression of a significant number of genes appears to be modified in response to light/darkness cycles and circadian oscillations, indicating that this type of control is not limited to certain specific features of cyanobacteria. Such broader impact on different physiological processes makes us question the premise of circadian rhythms being circumscribed to this particular group within prokaryotes.The presumed lack of circadian periodicity in the physiology of heterotr
%U http://www.jcircadianrhythms.com/content/8/1/8