Biochemical controls: circadian clock proteins (Introduction)

by David Turell , Wednesday, October 18, 2023, 20:16 (193 days ago) @ David Turell

In soil bacteria equal to Eukaryote types:

https://www.science.org/doi/full/10.1126/sciadv.adh1308

"Abstract
Circadian clocks are pervasive throughout nature, yet only recently has this adaptive regulatory program been described in nonphotosynthetic bacteria. Here, we describe an inherent complexity in the Bacillus subtilis circadian clock. We find that B. subtilis entrains to blue and red light and that circadian entrainment is separable from masking through fluence titration and frequency demultiplication protocols. We identify circadian rhythmicity in constant light, consistent with the Aschoff’s rule, and entrainment aftereffects, both of which are properties described for eukaryotic circadian clocks. We report that circadian rhythms occur in wild isolates of this prokaryote, thus establishing them as a general property of this species, and that its circadian system responds to the environment in a complex fashion that is consistent with multicellular eukaryotic circadian systems.

"Circadian clocks are complex intracellular molecular networks that structure processes over the 24-hour day. They are commonly described as having self-sustained, temperature-compensated daily rhythms that entrain to 24-hour cycles of cycling environmental time cues (zeitgebers). These endogenous timing mechanisms are pervasive throughout nature; they operate from the level of cell to organism and from mammals, plants, and fungi to bacteria. Within the prokaryotic kingdom, which accounts for over 10% of life on Earth, a powerful clock model system in the cyanobacteria has been elaborated. Circadian clocks in nonphotosynthetic bacteria have only been described recently, and their characteristics are not well known. We and others recently showed evidence of the “trilogy” of circadian clock properties described above in Bacillus subtilis and Klebsiella aerogenes.

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"In this study, we challenge the circadian clock of B. subtilis with respect to a catalog of chronobiology protocols. We use light as a zeitgeber to systematically probe the clock in this nonphotosynthetic bacterium. We found that this organism shares many circadian characteristics occurring in eukaryotic organisms, some of which have yet to be documented in established clock models in cyanobacteria or fungi.

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"Entrainment leads to the establishment of a stable phase relationship between the external (environmental) and the internal (circadian) time. Circadian systems use zeitgebers for entrainment, leading to a set of remarkable phenomena. We were surprised to observe that a prokaryote challenged with chronobiological protocols exhibits a variety of highly complex entrainment properties. For instance, aftereffects describe changes in the FRP following specific zeitgeber treatments. Commonly used protocols revealing such changes include T cycles (entrainment cycles of different lengths) or treatments with various zeitgeber structures. The presence of aftereffects (see table S1) suggests that information regarding zeitgeber exposure is stored, much like a memory. In the case of B. subtilis, the zeitgeber treatment is present as the circadian system forms, from inoculation to biofilm formation.

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"The task of the circadian clock is to “read” the local environment and, for many systems, this means harvesting not just one but many cues. We suggest that by using both blue and red light and temperature as zeitgebers, B. subtilis can fine-tune clock-regulated processes to a greater range of situations.

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"bacteria can sense light through nondedicated photoreceptor molecules. Fe/S clusters can absorb in the ultraviolet/visible part of the spectrum and have been implicated in circadian clock input pathway of cyanobacteria. Light can also entrain the cyanobacterial circadian clock via metabolism, by toggling the adenosine 5′-triphosphate/adenosine 5′-diphosphate (ATP/ADP) ratio. Furthermore, B. subtilis contains riboflavins (vitamin B2) and heme, which are light sensitive. Future studies are required to investigate which light-sensing molecules are involved in entraining the B. subtilis circadian system, which might also provide insights into the ecological and adaptive relevance of circadian programs in B. subtilis.

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"In conclusion, we find it remarkable that a relatively simple prokaryote, which lacks the obvious hierarchy of organization of multicellular organisms, evokes properties of complex circadian systems. This indicates that B. subtilis represents a powerful model system for the study of circadian clocks, given the scope of formal properties therein that it displays. It also tells us something about common elements of all circadian systems." (my bold)

Comment: I don't think it is remarkable that these bacteria have such a system. They represent the starting of evolution so why shouldn't they have it considering that on Earth we have 12-hour light cycles? I assume the first life (LUCA) arrived equipped with them. Designed that way before pre-evolution advances. Darwin doesn't try to explain this form of early life but presumes its unexplained beginning and then theorizes the after events.