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Cyanobacteria use a principle similar to AM radio to coordinate cell division with circadian rhythms by encoding information through pulse amplitude modulation. Cyanobacteria, an ancient group of photosynthetic bacteria, have been found to regulate their genes using the same physical principle used in AM radio transmission.
A new study published in Current Biology, found that cyanobacteria use variations in the amplitude (strength) of the pulse to transmit information in individual cells. The discovery sheds light on how biological rhythms work together to regulate cellular processes.
In AM (amplitude modulation) radio, a wave of constant strength and frequency, called a carrier, is generated by oscillating electrical current. An audio signal that contains information (such as music or speech) to be transmitted is superimposed on the carrier wave. This is done by changing the amplitude of the carrier wave according to the frequency of the audio signal.
A research team led by Professor James Locke of the University of Cambridge's Sainsbury Laboratory (SLCU) and Dr Bruno Martins of the University of Warwick has discovered that a similar mechanism, similar to AM radio, is at work in cyanobacteria.
In cyanobacteria, the cycle of cell division, the process in which one cell grows and divides into two new cells, acts as a "signal carrier." The modulating signal then comes from the bacterium's 24-hour circadian clock, which acts as an internal timekeeping mechanism.
Solving the ancient cellular puzzle
This discovery answers a long-standing question in cell biology – how do cells integrate signals from two oscillatory processes – the cell cycle and the circadian rhythm – that operate at different frequencies? Until now, it was not clear how these two cycles could be coordinated.
To solve the puzzle, the research team used single-cell time-lapse microscopy and mathematical modeling. Using time-lapse microscopy, they tracked the expression of the protein, the alternative sigma factor RpoD4. RPoD4 plays an important role in the initiation of transcription, which is the process by which genetic information from DNA is transcribed into RNA. The simulations allowed the researchers to study the mechanisms of signal processing by comparing the simulation results with the microscopy data. The team discovered that RpoD4 turns on pulses that occur only during cell division, making it an ideal candidate to track.
Lead author Dr. Chao Ye explained: "We found that the circadian clock determines how strong these impulses are over time. Using this strategy, cells can encode information about two oscillatory signals in a single output: cell cycle information in pulsation frequency and 24-hour clock information in pulsation strength. This is the first time we have observed a circadian clock that uses pulse amplitude modulation, a concept usually associated with communication technology, to control biological functions."
Consequences of conclusions
“Changing the frequency of the cell cycle due to ambient light or the circadian clock due to genetic mutations confirmed the basic principle. "It's amazing to see examples in nature of what we sometimes think of as 'our' engineering rules," said co-author Dr Martins. "A lineage of cyanobacteria evolved 2,7 billion years ago and has an elegant solution to this information processing problem."
Professor Locke added: "One of the reasons we study cyanobacteria is that they have the simplest circadian clock of any organism, so understanding this lays the foundation we need to understand clocks in more complex organisms such as humans and agricultural crops.
"These principles may have broader implications in synthetic biology and biotechnology. For example, it could help us grow crops that are more resilient to changing environmental conditions, with implications for agriculture and sustainable development."
