Integrating the Circadian Oscillator into the Life of the Cyanobacterial Cell

Abstract

In two decades, the study of circadian rhythms in cyanobacteria has gone from observations of phenomena in intractable species to the development of a model organism for mechanistic study, atomic-resolution structures of components, and reconstitution of a circadian biochemical oscillation in vitro. With sophisticated biochemical, biophysical, genetic, and genomic tools in place, the circadian clock of the unicellular cyanobacterium Synechococcus elongatus is poised to be the first for which a systems-level understanding can be achieved.

TRANSCRIPTIONAL ANALYSIS OF THE UNICELLULAR, DIAZOTROPHIC CYANOBACTERIUM CYANOTHECE SP. ATCC 51142 GROWN UNDER SHORT DAY/NIGHT CYCLES1

“…Circadian rhythms function to optimize specific physiological mechanisms to the correct time of day (Golden and Canales 2003, Golden 2007). We are particularly interested in the relationship of photosynthesis, which generates O 2 , to the O 2 ‐sensitive nitrogen fixation throughout a 24 h diurnal cycle.…”

“…However, the CikA kinase does not have a clear homolog in other cyanobacteria, including Cyanothece sp. ATCC 51142, and variations in the circadian mechanism should be considered the norm (Golden 2007, Mackey and Golden 2007).…”

Genetic circuitry controlling motility behaviors of Myxococcus xanthus

“…Oscillating phosphorelays have been proposed to control the cyanobacterial circadian clock. (48) Theoretically, introduction of a feedback mechanism within the Frz system would turn the pathway into a biochemical oscillator, which could then act as an internal clock to control reversals. (49) However, this is only an attractive hypothesis, because feedback is favored to occur at the level of the methyltransferase, yet, methylation changes have been shown to occur over a period of hours in response to repellent cues, (50) while reversals occur within a time domain of minutes.…”