Circadian regulation of metabolic, cell division, and cation transport promoters in the gastrointestinal bacterium .

Introduction: All eukaryotes and at least some prokaryotes express the capacity to anticipate and adapt to daily changes of light and temperature in their environments. These circadian programs are fundamental features of many forms of life. Cyanobacteria were the first prokaryotes to have demonstrated circadian gene expression.

Transcriptional effects of melatonin on the gut commensal bacterium Klebsiella aerogenes.

Klebsiella (nee Enterobacter) aerogenes is the first human gut commensal bacterium with a documented sensitivity to the pineal/gastrointestinal hormone melatonin. Exogenous melatonin specifically increases the size of macrocolonies on semisolid agar and synchronizes the circadian clock of K. aerogenes in a concentration dependent manner.

Context and novelty increase strength of auditory cues as a weak circadian zeitgeber in songbirds.

Light is the best-studied external cue (zeitgeber) for the entrainment of circadian rhythms. Non-photic entrainment is also possible; some organisms can entrain to rhythmic temperatures, drug administration, feeding, water turbulence, exercise and social cues. One such social cue that has the capacity to act as a weak zeitgeber to songbirds is the rhythmic presentation of conspecific vocalization.

Melatonin duration gates photoperiodic vocal state change in a songbird.

Seasonally breeding animals concentrate courtship to a particular time of year such that their offspring will be reared in a favorable environment. In house sparrows, Passer domesticus, primary (gonads) and secondary (song, plumage, beak color, etc) sexual characteristics are expressed differentially depending on the photoperiod. Removal of the pineal gland (PINX) has no effect on seasonal rhythms in gonad size but alters the photostimulated increase in vocal rate and complexity.