Can bacteria tell the time?

We can do it, and so can plants: tell the time of day based on our environment. How about bacteria?

Breaking down the microbiology world one bite at a time

Can bacteria tell the time?

Humans, animals and plants have a so-called ‘circadian rhythm’, which is an internal clock that follows a 24-hour cycle. Because it is primarily based on the natural cycle of dark and light, it is no surprise that this cycle has been found even in photosynthetic bacteria, which require light to make energy. However, until now researchers could not find such mechanisms in other, non-light-using bacteria. And why is this so important? Bacteria play a big role in ecology, as well as in health and industrial biotechnology. The possibility of taking advantage of this internal clock could have a big impact on applications that rely on timing such as biotechnology, drug delivery or agriculture protection.

For the first time, Zheng Eelderink-Chen and colleagues found such a clock in Bacillus subtilis, bacteria commonly found in the soil and the gastrointestinal tract of herbivorous mammals and humans. These bacteria are also quite interesting because they are used in biotechnological applications such as laundry detergent production and crop protection.

They looked at different zeitgebers (a German term, literally translated to ‘time giver’) to see how environmental cues influence certain processes going on in the cells. One of the processes they looked at was the blue light photoreceptor (coded by the gene ytvA), an integral part of all circadian systems examined so far, including plants and fungi. The second gene they focused on is involved in inducing formation of biofilms and spores in the bacterium (KinC).

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To measure the expression of these genes, they fused the luciferase gene to their respective promoters. This results in the production of a bioluminescent enzyme allowing the researchers to visualize how active the genes are in the bacteria.

The first zeitgeber they looked at was the natural cycle of light and darkness. The bacteria were subjected to 12-hour periods of light and darkness while they measured the bioluminescence of luciferase: they found that the levels of ytvA and KinC increased during the dark period, and decreased in the light! This cycle was still observed when they left the bacteria constantly in the dark, but was slowly diminished after a few days.

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Similar experiments were performed with daily temperature changes: growing 12 hours at 25,5°C and 28,5°C. Surprisingly, in contrast to the cycles in light/darkness, gene activity was generally higher during the warm phase (corresponding to daytime). The researchers also show that the circadian rhythms they detected depend upon environmental characteristics such as nutrient supply and ambient temperature. In addition, only the cultures that formed a biofilm showed circadian rhythms.

This research could be the beginning of a new line of questions: Is the time of day of bacterial exposure important for infection? Can we optimize biotechnological processes if we take the time of day into account? Now it is demonstrated that bacteria can tell the time, they’ll have to find out why having this mechanism is an advantage for the bacteria.

Learn more about B. subtilis:

Original paper: Zheng Eelderink-Chen, Jasper Bosman, Francesca Sartor, Antony N. Dodd, Ákos T. Kovács, Martha Merrow A circadian clock in a nonphotosynthetic prokaryote Science Advances08 Jan 2021

Doi: 10.1126/sciadv.abe2086