Publications Publications This list includes publications from onwards. You can use PubMed to browse citations for our older publications Experimental Brain Research, Sanes Classification of multivariate non-stationary signals:
Abstract Circadian rhythms are fundamental properties of most eukaryotes, but evidence of biological clocks that drive these rhythms in prokaryotes has been restricted to Cyanobacteria.
Here, we demonstrate at least one species of commensal bacterium from the human gastrointestinal system, Enterobacter aerogenes, is sensitive to the neurohormone melatonin, which is secreted into the gastrointestinal lumen, and expresses circadian patterns of swarming and motility.
Melatonin specifically increases the magnitude of swarming in cultures of E. The swarming appears to occur daily, and transformation of E. Altogether, these data demonstrate a circadian clock in a non-cyanobacterial prokaryote and suggest the human circadian system may regulate its microbiome through the entrainment of bacterial clocks.
These bacteria express circadian patterns of gene expression, photosynthesis and nitrogen fixation [ 1 — 3 ], but the molecular mechanism for this cyanobacterial clock is the result of rhythmic autokinase activity of the hexamer-forming ATPase KaiC that is enhanced by KaiA binding and subsequent autophosphatase activity of KaiC that is modulated by KaiB binding to the KaiA-KaiC complex [ 4 ].
Remarkably, the three purified proteins, when provided free ATP, exhibit rhythmic phosphorylation of KaiC in vitro for many cycles [ 5 ]. Among the vertebrate peripheral tissues that express circadian rhythms Acuna manual binder the gastrointestinal system, which exhibit circadian rhythms in gene expression including clock genesmotility and secretion in vivo and in vitro [ 10 — 12 ].
They are also coordinated by SCN input via the sympathetic nervous system [ 13 ]. The emerging role of the gut microbiome as an important modulator of gastrointestinal function has recently included the role of circadian rhythms. Recent studies have suggested that microbial signaling plays a critical role in homeostatic maintenance of intestinal function along with the host circadian mechanism [ 1415 ].
Further studies have expanded this view and have shown that disruption of the circadian clock, either via dietary restriction or phase shifting e. While it is clear from these studies that commensal bacteria and gut tissues do communicate, it is not clear which signal or signals the microbiome exploits to sustain its own homeostasis.
Here we present evidence for one possible signal, the indole hormone melatonin, which is present at high levels in the gut and which induces swarming activity in a clinical isolate of Enterobacter aerogenes. Further investigation of the motility patterns in this bacterium evinced an endogenous circadian rhythm within cultures, which is enhanced and synchronized by melatonin.
Materials and Methods Strains and culture conditions: All chemicals used in motility assays were purchased from Sigma St. Louis, MO and diluted in water. Transformants were selected for on tetracycline-supplemented medium and stored as glycerol stocks for future studies.
Plates were sealed with 40mm cover glass by sterile vacuum grease and placed into an automated photomultiplier-based bioluminescence recorder Lumicycle, Actimetrics, Il. Each sample was counted for 70 seconds on a rotating platform.
Raw bioluminescence baselines were subtracted using a hour running average via Lumicycle Analysis software Actimetrics, IL. Cultures were photographed as above and used for illustrative purposes here.
Circadian rhythmicity was determined by Circwave, Circwave Batch software v3. Periodogram analysis was performed using R statistical program and the GeneCycle package [ 26 ] followed by Fisher's exact g Test to obtain p-values of each culture.
Results and Discussion We hypothesized that one potential human signal that may affect gastrointestinal microbiota is the secretion of melatonin into the lumen of the gut. Although melatonin is widely regarded as a pineal and retinal neuromodulator of circadian and photoperiodic function [ 2728 ], it is present throughout the gastrointestinal system [ 27 — 29 ], in part from pineal melatonin secretion [ 3031 ], but there is evidence for melatonin biosynthetic enzymes in biliary cholangiocytes, enterochromaffin cells and intestinal mucosa [ 3132 ].
In addition, many foods contain melatonin [ 2731 ]. In all, melatonin content has been reported to be x levels found in the serum [ 3132 ].
These included receptors in Enterobacter aerogenes, but not in Escherichia coli or Klebsiella pneumoniae. Colonies formed by clinical isolates of Enterobacter aerogenes, a Gram negative, indole-negative motile bacterium, proliferated on semi-solid Agar significantly more rapidly in the presence of melatonin in a specific, dose-dependent fashion, with maximal response coinciding within the physiological range of gut melatonin levels Fig 1A and 1B and S2 Fig.
This effect was specific for melatonin, as E.A leading manufacturer of accessories for land surveying, global positioning system, construction, monitoring and agriculture equipment, SECO engineers products to make professional field equipment more productive and efficient.
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