People, animals, and plants have internal clocks. A new study, published in Science Advances, has shown that bacteria also have them and correspond to our planet’s 24-hour cycle.
Biological clocks, or circadian rhythms, are internal synchronization mechanisms that are widespread in nature, enabling living organisms to cope with major changes from day to night, even in different seasons.
These molecular rhythms inside cells use external signals, such as daylight and temperature, to synchronize the biological clock with the environment. This is why humans experience dramatic changes in well-being and perception when jet lagging – our internal clocks temporarily do not match before aligning with the new cycle of light and darkness at our destination.
A growing body of research has demonstrated the importance of molecular clocks for basic processes such as sleep and cognitive function in humans and water regulation and photosynthesis in plants over the past two decades.
Although bacteria makeup 12% of the planet’s biomass and are important for health, ecology, and industrial biotechnology, little is known about their 24-hour biological clock. Previous research has shown that photosynthetic bacteria, which require light to generate energy, have a biological clock. But free-living non-photosynthetic bacteria in this respect remained a mystery.
In this international study, scientists discovered free circadian rhythms in non-photosynthetic soil bacteria, Bacillus subtilis. The team used a luciferase reporting technique, which involves adding an enzyme that produces bioluminescence, allowing researchers to visualize how active a particular gene is within the body.
“Bacillus subtilis is used in a variety of fields, from laundry detergents to plant protection, in addition to the recent use of human and animal probiotics, so the development of a biological clock for this bacterium will be a culmination. In various biotechnological fields”.
Professor Akos Kovacs, Technical University of Denmark
They focused on two genes: ytvA, which encodes a blue-light photoreceptor, and an enzyme called KinC, which is involved in inducing biofilm and spore formation in bacteria.
They observed gene levels in constant darkness compared to cycles of 12 hours of light and 12 hours of darkness. They found that the ytvA levels’ structure was adjusted to the cycle of light and dark, with levels increasing in darkness and decreasing in light. The cycle was still observed in constant darkness.
“We have discovered for the first time that non-photosynthetic bacteria can tell time. They adapt their molecular work to the time of day by reading cycles under light or in a temperature environment.””
Professor Martha Murrow from Ludwig Maximilian University in Munich
The researchers noticed that 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 “obey” environmental cues.
They conducted similar experiments using daily temperature changes, for example, by increasing the length or strength of the diurnal cycle and found that the ytvA and kinC rhythms were regulated following circadian rhythms and not just turned on and off in response to temperature.