Despite constituting over 10% of all life forms, bacteria have often been overlooked for their complexity. Recent discoveries have shown that like humans, soil-dwelling bacteria also possess internal rhythms, known as circadian clocks, that align their actions with Earth’s day-night cycle.

Pioneering research has shed light on the intricate nature of these bacterial circadian clocks, paving the way for a new era of scientific exploration. Such studies could lead to wide-ranging applications, from accurately scheduling antibiotic use to bioengineering more efficient gut and soil microbiomes.

The discovery is credited to a joint research effort involving Ludwig Maximillian University Munich (LMU Munich), The John Innes Centre, The Technical University of Denmark, and Leiden University. They delved into gene expression patterns in the prevalent soil bacterium Bacillus subtilis to reveal the presence of circadian activity.

According to the main author, Dr. Francesca Sartor (LMU Munich), “The circadian clock in this microbe is pervasive: we see it regulating several genes, and a range of different behaviours.”

Professor Antony Dodd of the John Innes Centre expressed surprise that “a unicellular organism with such a small genome has a circadian clock with some properties that evoke clocks in more complex organisms.”

Earlier research by the same team had already demonstrated the presence of a circadian clock in a lab-based strain of this bacterium, using a technique that involved inserting a light-emitting enzyme, luciferase, which activates when a gene is expressed. This light guided the researchers in tracking the bacterial clock under changing conditions.

The study’s senior author, Professor Martha Merrow at LMU Munich, noted that the research highlights the ubiquity of circadian clocks in Bacillus subtilis.

“We might capitalize on knowledge of the clock to improve health outcomes and increase sustainability of food production or biotechnology.”

The study stands out because it demonstrates that these internal clocks are not just present in lab-grown strains but also those collected from natural habitats, hinting at the broad prevalence of these clocks in Bacillus subtilis. Moreover, the bacteria consistently exhibit circadian rhythms, whether in constant light or darkness, with the researchers documenting refined responses typically associated with the circadian clocks in other organisms. This indicates that bacteria can attune their bodily functions and metabolism to the shifting times of day and varying light and temperature conditions, much like their more complex counterparts.

This revelation opens new possibilities in biotech, health, and plant science. By deciphering the workings of bacterial circadian clocks, we could leverage microbial applications in industry, gain insights into microbiome formation, and understand the timing of antibiotic efficacy against harmful bacteria. This knowledge could also aid crop protection, as Bacillus subtilis is a beneficial soil bacterium that farmers use to facilitate nutrient exchange, support plant growth, and guard against harmful microbes.

The research team is currently developing Bacillus subtilis as a model to study bacterial circadian clocks. The focus is now on identifying the genes that constitute this clock mechanism and understanding how the circadian clock of B. subtilis depends on multicellular organization for optimal performance.

Circadian clocks, or internal oscillators, provide a survival advantage to organisms by enabling their bodily functions and metabolism to adapt to 24-hour environmental changes, like shifts in light, temperature, or predator behavior. They’re also the reason behind the unsettling effects of jet lag when we cross time zones.

Drawing a parallel with French biologist Jacques Monod’s statement that ‘What is true for E. coli is true for the elephant,’ Professor Ákos T. Kovács from Leiden University and Technical University of Denmark found it fascinating that “the circadian clock in Bacillus subtilis– a bacterium with just four thousand genes – has a complex circadian system that is reminiscent of circadian clocks in complex organisms such as flies, mammals, and plants”.

The results, revealing the complex circadian systems of the bacterium B. subtilis, were published in Science Advances.

Source: 10.1126/sciadv.adh1308

Image Credit: Ella Baker – Jack Dorling John Innes Centre.