‘Ice Bucket Challenge’ Reveals Bacteria Can Anticipate Seasons

Bacteria use their internal 24-hour clock to anticipate the arrival of new seasons, according to research using an “ice bucket challenge.”

The discovery could have profound implications for understanding the role that circadian rhythms – a molecular version of a clock – play in helping species adapt to climate change, from migratory animals to flowering plants.

The team behind these results subjected populations of blue-green algae (cyanobacteria) to different artificial day lengths at a constant, warm temperature. The samples placed on plates received either short days, equinox days (equal light and darkness), or long days, for eight days.

After this treatment, the blue-green algae were immersed in ice for two hours and survival rates were monitored.

Samples that had been exposed to a succession of short days (eight hours of light and 16 hours of darkness) in preparation for the icy challenge achieved survival rates of 75%, up to three times higher than colonies that had not been prepared in this way.

A single day was not enough to increase the bacteria’s resistance to cold. It was only after a few days, ideally six to eight days, that the bacteria’s chances of survival improved significantly.

In cyanobacteria whose genes that make up their biological clock were deleted, survival rates were the same regardless of day length. This indicates that photoperiodism (the ability to measure the day-night cycle and change physiology in anticipation of the upcoming season) is essential to prepare bacteria for long-term environmental changes such as a new season or climate change.

“The results indicate that bacteria in nature use their internal clock to measure day length and when the number of short days reaches a certain point, as it does in autumn, they ‘switch’ to a different physiology in preparation for the winter challenges ahead,” explained the study’s first author, Dr Luísa Jabbur, who was a researcher at Vanderbilt University in Tennessee in Professor Carl Johnson’s lab when this study took place, and is now a BBSRC Discovery Fellow at the John Innes Centre.

The Johnson lab has long studied the circadian clock in cyanobacteria, both from mechanistic and ecological perspectives.

Previous studies have shown that bacteria have a version of a biological clock, which could allow them to measure the differences in length between day and night, providing an evolutionary advantage.

This study, which appears in ScienceThis is the first time anyone has shown that photoperiodism in bacteria has evolved to anticipate seasonal signals.

These results open new horizons of scientific exploration. A key question arises: how does an organism with a lifespan of between six and 24 hours manage to develop a mechanism that allows it not only to react to future conditions, but also to anticipate them?

“It’s like they’re signaling to their daughter cells and their grandchildren, telling them that the days are getting shorter and they need to do something,” Dr. Jabbur said.

Dr Jabbur and colleagues at the John Innes Centre, as part of his BBSRC Discovery Fellowship, will use cyanobacteria as a fast-reproducing model species to understand how photoperiodic responses might evolve in other species during climate change, with promising applications to major crops.

A key part of this work will be to better understand the molecular memory systems by which information is transmitted from generation to generation within species. Research will focus on the possibility that an accumulation of compounds during the night during short days acts as a molecular switch that triggers a change in physiology or phenotype.

For Dr Jabbur, the results represent an early scientific breakthrough, despite initial scepticism from his scientific mentor and corresponding author of the paper, Professor Carl Johnson.

“In addition to being a fascinating and inspiring person, Carl sings in the Nashville Symphony chorus and has an operatic laugh! This resonated with the department when I first presented my idea for the ice challenge, to see if photoperiod was a signal for cyanobacteria in their natural element,” Dr. Jabbur said.

“To be honest, he told me to go and try it, and as I was going, he pointed out a sign on his door with the Frank Westheimer quote: Progress is made by young scientists doing experiments that old scientists say wouldn’t work.”

“It worked the first time. Then I repeated the experiments. There is something very valuable about looking at a series of plates containing bacteria and realizing that at that moment you know something that no one else knows.”