In a first-of-its-kind discovery, scientists have discovered that a species of non-photosynthetic bacteria is regulated by the same circadian rhythms that hold sway over so many other life forms.
In humans, our circadian rhythms act as a kind of biological clock in our cells, controlling virtually all processes in our body, affecting when we sleep and wake up, plus the functioning of our metabolism and cognitive processes.
This internal timekeeping, which runs on a 24-hour cycle, is driven by our circadian clock, and the same core phenomenon has been observed in many other types of organisms, including animals, plants, and fungi.
However, it has long been unclear whether bacteria in general are also subject to the dictates of circadian rhythms.
The phenomenon has been demonstrated in photosynthetic bacteria, which use light to make chemical energy, but whether other types of bacteria also possess circadian clocks has long remained a mystery until now.
“We have discovered for the first time that non-photosynthetic bacteria can tell time,” explains chronobiologist Martha Merrow of Ludwig Maximilian University of Munich.
“They adapt their molecular activity to the time of day by reading the cycles in the light or in the temperature environment.”
In a new study, Merrow and fellow researchers investigated Bacillus subtilis, a strong, well-studied bacteria found in the soil and gastrointestinal tract of many animals, including humans.
While B. subtilis is not photosynthetic, it is sensitive to light thanks to photoreceptors, and previous observations of the microbe have indicated that its gene activity and biofilm-forming processes can follow a daily cycle in response to environmental factors, perhaps based on light levels or temperature changes.
To investigate this, the researchers measured the bacteria’s gene expression activity 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 codes for a blue light photoreceptor – increased during the dark phase and decreased during the light phase, indicating entrainment processes in a circadian clock.
When subjected to constant darkness, the cycle still existed B. subtilisalthough the period got longer, not strictly on a 24 hour cycle without the light signal to go out.
In another experiment, the researchers experimented with temperature cycling, another way of stimulating changes in heat between day and night.
Again, ytvA expression ebbed and flowed as the temperature continued 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 remained in a free-running experiment (not synchronized with environmental factors) although with a longer period.
All results added together, the researchers conclude B. subtilis has a circadian clock, displayed by free-running circadian rhythms and systematic entrainment into environmental cues known as zeitgeber cycles.
Although the findings only concern one bacterial species for now, this is the first time this phenomenon has occurred in a non-photosynthetic bacterium, which could have major implications for our understanding of bacteria as a whole: organisms that make up about 15 percent of bacteria . living matter on Earth.
“Our study opens doors to investigate circadian rhythms through bacteria,” said circadian rhythm researcher Antony Dodd of the John Innes Center in the UK.
“Now that we have established that non-photosynthetic bacteria can see how much time it takes us to figure out the processes in bacteria that cause these rhythms, and understand why having a rhythm benefits bacteria.”
For now, the team speculates that circadian rhythms may be somehow regulated by a feedback system for transcription translation, or linked to metabolic cycles.
It is also unknown if some form of global ‘master clock’ could control in some way B. subtilisIt’s circadian timekeeping, as has been suggested in humans, although the team indicates this is a possibility.
“It will be informative to investigate whether temperature and light are inputs to one master pacemaker or not B. subtilis can have multiple oscillators, as described for a variety of unicellular and multicellular organisms, ‘the authors write in their paper.
“It is also possible that B. subtilis can have either a master oscillator or one or more downstream oscillators coupled to and carried by a master pacemaker. “
In any case, the implications of a 24-hour body clock in bacteria can have enormous implications – 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 is used in a variety of applications, from detergent production to crop protection … [and] human and animal probiotics, ”says bio-engineer Ákos Kovács from the Technical University of Denmark.
“For example, the development of a biological clock in this bacterium will culminate in various biotechnological areas.”
The findings are reported in Science Advances.