Even basic bacteria can forecast seasonal shifts

Despite being one of the simplest life forms on Earth, cyanobacteria are able to predict and prepare for seasonal changes based on the amount of light they receive.

It has been known for over a century that complex organisms can use day length as a cue to future environmental conditions – for example, days shortening before cold weather sets in. Phenomena such as plant and animal migration, flowering, hibernation and seasonal reproduction are all guided by such responses, known as photoperiodism, but this has not previously been seen in simpler life forms such as bacteria.

Luisa Jabbour Later, at Vanderbilt University in Nashville, Tennessee, colleagues artificially Synechococcus elongatus By exposing the cyanobacteria to different day lengths, they found that those that experienced simulated short days were two to three times better able to survive icy temperatures, preparing them for winter-like conditions.

By testing shorter and longer durations, the researchers found that it took four to six days for a response to appear.

Because these organisms can produce new generations within a matter of hours, their cells must pass on information about the length of daylight to their offspring, but researchers don’t yet understand how this information is transmitted.

Cyanobacteria, which capture energy from sunlight through photosynthesis, have been around for more than two billion years and are found almost everywhere on Earth.

“The fact that organisms as ancient and simple as cyanobacteria have a photoperiodic response suggests that this is a phenomenon that has evolved much longer than we had imagined,” says Jabbour, who is now at the John Innes Centre in Norwich, UK.

The team also looked at how gene expression patterns change in response to changes in day length, suggesting that photoperiodism likely evolved by exploiting existing mechanisms to cope with acute stresses such as bright light and extreme temperatures.

These findings also have implications for the evolution of circadian rhythms, the internal clocks that regulate day-night cycles, team members say. Karl Johnson At Vanderbilt University.

“I think we’ve always thought that circadian clocks evolved before organisms were able to measure the length of days and nights and predict the changing of seasons,” he says, “but the fact that photoperiodism evolved in such ancient, simple organisms, and that our gene expression results are linked to stress response pathways that seem to have evolved very early in life on Earth, suggests that photoperiodism may have evolved before the circadian clock,” Johnson says.