A team of researchers from Germany, Denmark and the United Kingdom has identified circadian rhythms in non-photosynthetic, Gram-positive bacterium Bacillus subtilis.
Bacillus subtilis. Image credit: Ákos Kovács, Technical University of Denmark.
Circadian rhythms are exquisite internal timing mechanisms that are widespread across nature enabling living organisms to cope with the major changes that occur from day to night, even across seasons.
Existing inside cells, these molecular rhythms use external cues such as daylight and temperature to synchronize biological clocks to their environment.
Although bacteria represent 12% biomass of the planet and are important for health, ecology, and industrial biotechnology, little is known of their 24-hr biological clocks.
Previous studies have shown that photosynthetic bacteria which require light to make energy have biological clocks.
“We’ve found for the first time that non-photosynthetic bacteria can tell the time,” said senior author Professor Martha Merrow, a researcher in the Institute of Medical Psychology at the Ludwig Maximilians University Munich.
“They adapt their molecular workings to the time of day by reading the cycles in the light or in the temperature environment.”
The scientists applied a technique which involves adding an enzyme that produces bioluminescence that allows them to visualize how active a gene is inside an organism.
They focused on two genes: firstly, a gene called ytvA which encodes a blue light photoreceptor and secondly an enzyme called KinC that is involved in inducing formation of biofilms and spores in the bacterium.
They observed the levels of the genes in constant dark in comparison to cycles of 12 hours of light and 12 hours of dark.
They found that the pattern of ytvA levels were adjusted to the light and dark cycle, with levels increasing during the dark and decreasing in the light. A cycle was still observed in constant darkness.
The team observed how it took several days for a stable pattern to appear and that the pattern could be reversed if the conditions were inverted.
These two observations are common features of circadian rhythms and their ability to entrain to environmental cues.
The authors carried out similar experiments using daily temperature changes.
For example, increasing the length or strength of the daily cycle, and found the rhythms of ytvA and kinC adjusted in a way consistent with circadian rhythms, and not just simply switching on and off in response to the temperature.
“Our study opens doors to investigate circadian rhythms across bacteria,” said co-author Dr. Antony Dodd, a researcher in the John Innes Centre.
“Now that we have established that bacteria can tell the time we need to find out the processes that cause these rhythms to occur and understand why having a rhythm provides bacteria with an advantage.”
The discovery is reported in a paper in the January 8, 2021 edition of the journal Science Advances.
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Zheng Eelderink-Chen et al. 2021. A circadian clock in a nonphotosynthetic prokaryote. Science Advances 7 (2) eabe2086; doi: 10.1126/sciadv.abe2086
