Organisms throughout nature have an internal biological clock within them known as the circadian rhythm. For humans and animals, our brains send out molecular signals to the body following light cues in order to synchronize our sleep and eating cycles to the day and night cycle. For plants, the opening and closing of flower petals are also governed to match the day and night cycle. Studies have shown that photosynthetic bacteria, which are bacteria that require light to make energy, have an internal clock too, but it is unknown whether the same is true for non-photosynthetic bacteria, which comprise the majority of the bacteria on Earth. A recent study revealed, for the first time, that a particular non-photosynthetic bacterium, Bacillus subtilis, does have a circadian rhythm.

To figure out if an organism has a circadian rhythm, scientists typically look for a molecule or gene within the organism that satisfies three conditions. The first condition is that it must have an internal, periodic cycle that runs even without any environmental cues (for example, a plant will still open and close its flower petals periodically even if you place it inside a black box). This is known as a free-running cycle. Secondly, the cycle must be able to respond to environmental cues such as light; as you vary the dark/light cycle a plant receives, the cycle of the flower petals opening and closing will adapt and match it. This is known as entrainment. Lastly, circadian clocks are usually insensitive to temperature — within a certain limit, temperature fluctuations do not affect your internal biological clock. This is known as temperature compensation.

In the study, Eelderink-Chen et al. found that Bacillus subtilis has a gene that satisfies all three conditions. Specifically, they studied ytvA, a gene encoding a light receptor in the bacteria. The gene has a free-running cycle that can be entrained using a dark/light cycle, and the cycle is not affected by variations in temperature. Therefore, these scientists showed that circadian rhythm exists within Bacillus subtili, which is the first time that this phenomenon has been shown in a non-photosynthetic bacterium. This study opens the door to studying and understanding circadian rhythm in bacteria as a whole. This could particularly benefit industries that utilize bacteria —for example, for biotechnologies that uses bacteria to make medicines and other biological products, it will certainly be useful to know when the bacteria is awake and active, or asleep and sluggish.

Zheng Eelderink-Chen is a PhD student in the Department of Psychology at Ludwig Maximilian University (LMU) of Munich, while Jasper Bosman is a researcher at Hanze University of Applied Sciences.

Managing Correspondent: Wei Li

Press Article: In First-of-Its-Kind Discovery, Scientists Confirm Bacteria Have a 24-Hour Body Clock, Science Alert.

Bacteria Have Internal Clocks Too, Technology Networks.

Original Article: A circadian clock in a nonphotosynthetic prokaryote, Science Advances.

Image Credit: congerdesign from Pixabay

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