In an unprecedented discovery, scientists found that a species of non-photosynthetic bacteria is regulated by the same circadian rhythms that control so many other forms of life.
In humans, our circadian rhythms act as a kind of biological clock in our cells, controlling virtually all processes in our bodies, influencing when we sleep and wake up, in addition to the functioning of our metabolism and cognitive processes.
This internal timing, which revolves around a 24-hour cycle, is driven by our circadian clock, and the same central phenomenon has also been observed in many other types of organisms, including animals, plants and fungi.
For a long time, however, it has not been clear whether bacteria in general are also subject to the dictates of circadian rhythm.
The phenomenon has been demonstrated in photosynthetic bacteria, which use light to produce chemical energy, but whether other types of bacteria also have circadian clocks is a mystery – until now.
“We discovered for the first time that non-photosynthetic bacteria can tell the time,” explains chronobiologist Martha Merrow, from Ludwig Maximilian University in Munich.
“They adapt their molecular functioning to the time of day, reading cycles in light or at room temperature.”
In a new study, Merrow and other researchers examined Bacillus subtilis, a resistant and well-studied bacterium found in the soil and gastrointestinal tract of many animals, including humans.
While B. subtilis it is not photosynthetic, it is sensitive to light thanks to photoreceptors, and previous observations of the microbe have hinted that its genetic activity and biofilm formation processes may follow a daily cycle in response to environmental stimuli, perhaps based on light levels or changes temperature.
To investigate, the researchers measured the expression activity of the bacterium gene in cultures exposed to constant darkness or an alternating daily cycle of 12 hours of light followed by 12 hours of darkness.
In the alternating light / dark cycle, the expression of a gene called ytvA – which encodes a blue light photoreceptor – increased during the dark phase and decreased during the light phase, indicative of entrainment processes in a circadian clock.
When subjected to constant darkness, the cycle still existed in B. subtilis, although the period has lengthened, not strictly following a 24-hour cycle with no light signal to turn off.
In another experiment, the researchers experimented with temperature cycles, which is another way of stimulating changes in heat between day and night.
Again, ytvA expression decreased and flowed as temperatures cycled between 12 hours at 25.5 ° C (77.9 ° F) and 12 hours at 28.5 ° C (83.3 ° F) and, as with light, the cycle persisted in a free experiment cycle (not synchronized with the environmental clues), although with a longer period.
Putting all the results together, the researchers conclude B. subtilis it has a circadian clock, exhibited by circadian rhythms of free execution and systematic dragging for environmental signals known as zeitgeber cycles.
Although the findings concern only one bacterial species for the time being, it is the first time that this phenomenon has occurred in any non-photosynthetic bacteria, which can have vast implications for our understanding of bacteria as a whole: organisms that represent about 15 percent percent of living matter on Earth.
“Our study opens doors to investigate circadian rhythms in bacteria,” said circadian rhythm researcher Antony Dodd of the John Innes Center in the United Kingdom.
“Now that we have established that non-photosynthetic bacteria can tell the time, we need to find out the processes in the bacteria that cause these rhythms to occur and understand why having a rhythm gives bacteria an advantage.”
For now, the team speculates that circadian rhythms may somehow be regulated by a transcription-translation feedback system or may be linked to metabolic cycles.
It is also not known whether a general form of ‘master clock’ can somehow control B. subtilisThe circadian timing of, as has been suggested in humans, although the team indicates that it is a possibility.
“It will be informative to investigate whether temperature and light are input to a master pacemaker, or whether B. subtilis may have several oscillators, as described for a variety of single-cell and multicellular organisms, “write the authors in their article.
“It is also possible that B. subtilis it can have a master oscillator or one or more downstream oscillators that are coupled and driven by a main pacemaker. “
In any case, the ramifications of a 24-hour biological clock on bacteria can have huge ramifications – not only in terms of scientific understanding of bacterial biology, but also in its potential use in biomedical science, agriculture, industry and beyond.
“Bacillus subtilis it is used in various applications, from the production of laundry detergent to crop protection … [and] human and animal probiotics “, says bioengineer Ákos Kovács, from the Technical University of Denmark.
“Thus, the engineering of a biological clock in this bacterium will culminate in several biotechnological areas.”
The results are reported in Advances in Science.