Bacterial bioclock

The ebb and flow of our daily lives revolves largely around our sleep cycle, which is governed by our body’s biological clock. Other animals and plants also have these internal timing mechanisms to cope with light changes across days and even seasons – and now researchers have discovered that bacteria do, too.

“We’ve found for the first time that non-photosynthetic bacteria can tell the time,” says lead author Martha Merrow, a chronobiologist from Ludwig Maximilians University (LMU), in Munich, Germany.

“They adapt their molecular workings to the time of day by reading the cycles in the light or in the temperature environment.”

The study, published in the journal Science Advances, may have implications in biotechnology, such as crop protection and the timing of drug delivery.

Research into biological clocks has been steadily accumulating over the past two decades, as they are essential in processes like sleep and cognitive functions in humans, and photosynthesis and water regulation in plants. But even though bacteria make up 12% of the biomass on the planet, they have largely remained a mystery.

Previous studies showed that photosynthetic bacteria – which use light to create energy – have internal molecular metronomes, and this research now demonstrates the same in non-photosynthetic bacteria.

It focuses on Bacillus subtilis, a species found in soil and the digestive systems of ruminant animals and humans.

According to Ákos Kovács, a co-author from the Technical University of Denmark, “Bacillus subtilis is used in various applications from laundry detergent production to crop protection, besides recently exploiting as human and animal probiotics.” Understanding these essential processes could lead to applications across biotechnology.

The team used a technique called luciferase reporting, which stimulates bioluminescence within the bacteria and allows researchers to visualise how active certain genes are under different conditions.

They chose two genes – one (ytvA) that encodes a blue-light photoreceptor, and one (kinC) that aids in the formation of biofilms and spores – and observed them in constant dark, as well as over cycles of 12 hours of light and 12 hours of dark.

They found that ytvA levels adjusted to the light and dark cycle – increasing during the dark and decreasing in light – though it took several days for a stable pattern to appear. The researchers also noticed that the pattern reversed when the conditions were inverted. These are common features of circadian rhythms, which are reliant on environmental cues.

Similar experiments focused on temperature changes; these indicated that adjustments in ytvA and kinC levels were consistent with circadian rhythms, instead of merely switching on and off at certain temperatures.

The researchers now face a whole host of new questions, such as whether the time of day that other organisms are exposed to bacteria is important to infection.

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

“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.”

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