Biological punctuality: Study finds even bacteria has an internal clock, can ‘tell time’

NORWICH, United Kingdom — Humans, animals, and plants all have an internal clock, or circadian rhythm. This internal timer is why people tire at night and wake up in the morning. Now, a fascinating new study reports even microscopic bacteria have an internal clock that aligns with the planet’s 24-hour cycle.

Researchers from the John Innes Centre say their discovery holds implications across a variety of fields, such as drug delivery timing, creating new and timely solutions for crop protection, and biotechnology.

Each organism’s molecular rhythms use external cues like sunlight and temperature to synchronize biological clocks with living environments. For example, this is why people often experience jet lag after traveling between time zones. Their bodies haven’t adapted and aligned to the new location’s light/dark cycle.

Meanwhile, circadian rhythms in plants are essential to processes like photosynthesis and water regulation.

Bacteria gets jet lag too?

Circling back to bacteria, these biological cells make up roughly 12 percent of the biomass on Earth. The term “bacteria” usually has a negative connotation, but these organisms are actually essential to a number of important life areas like human gut health, ecology, and industrial biotechnology. However, up until now little to nothing had been known regarding the internal clocks of bacteria.

Now, researchers have detected for the first time ever circadian rhythms in the non-photosynthetic soil bacterium Bacillus subtilis. This revelation was made possible thanks to a process called luciferase reporting. Scientists add a bioluminescent enzyme to an organism to visualize the activity of internal genes.

Shining a light on internal clocks – the bacterium Bacillus subtilis. (Credit:
Professor Ákos Kovács, Technical University of Denmark)

Study authors focused on two genes specifically; ytvA, which encodes a blue light photoreceptor, and an enzyme called KinC that helps induce the formation of biofilms and spores in the bacterium.

The study observed and tracked gene levels during a 12-hour period of light and 12-hour period of darkness before comparing them to a full 24 hours of darkness. Sure enough, ytvA levels adjusted to the light and dark cycle (levels increased at night and vice versa). Even in constant darkness, researchers still noted a more subdued internal cycle.

Just like an American re-adjusting to east coast time after a trip to Paris, it took several days of a steady day/night cycle for the bacteria to settle into a stable “pattern” again. Moreover, these patterns can even be reversed if scientists invert the conditions. Both of those observations are consistent with circadian rhythms among humans, animals, and plants.

‘They adapt to the time of day by reading cycles in the light or in the temperature’

The international team carried out similar experiments in regards to temperature, and once again both ytvA and kinC rhythms adapted in a manner consistent with circadian rhythms.

“We’ve found for the first time that non-photosynthetic bacteria can tell the time,” says lead author Professor Martha Merrow from Ludwig Maximilians University in a release. “They adapt their molecular workings to the time of day by reading the cycles in the light or in the temperature environment.”

“In addition to medical and ecological questions we wish to use bacteria as a model system to understand circadian clock mechanisms. The lab tools for this bacterium are outstanding and should allow us to make rapid progress.”

Study authors add this work can help answer numerous questions, such as: Does it matter at what time of day a bacterial infection occurs? Should industrial biotechnological processes consider time of day? Is the time of day of anti-bacterial treatment important?

“Our study opens doors to investigate circadian rhythms across bacteria. 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,” says co-author Dr. Antony Dodd from the John Innes Centre.

“Bacillus subtilis is used in various applications from laundry detergent production to crop protection, besides recently exploiting as human and animal probiotics, thus engineering a biological clock in this bacterium will culminate in diverse biotechnological areas,” concludes Professor Ákos Kovács, co-author from the Technical University of Denmark.

The study is published in Science Advances.