Even bacteria button up for winter. Photoperiodism might have evolved before circadian clocks

Amazing stuff!

"As winter approaches ... chronobiologists have shown that at least one kind of bacterium also prepares for the cold season—the first such seasonal response known among microbial life ...

When chilled, microbes increase the proportion of unsaturated fats in their membranes to keep them from freezing. ...

Not only did they make their membranes more fluid, but they also altered gene activity, the team reports. In anticipation of winter, when photosynthesis slows, the cyanobacteria revved up genes for conserving energy. When days got longer, they increased the activity of genes that protect against damage from sunlight. ..."

"... “To me, the most exciting thing about these results are their ramifications for the evolution of biological timekeeping,” he said. “I think we ‘chronobiologists’ have always assumed that daily (circadian) clocks evolved before organisms could measure day/night-length and thereby anticipate the changing seasons. But the facts that
(1) photoperiodism evolved in such ancient and simple organisms, and
(2) our gene expression results implicate stress response pathways that probably evolved very early in life on Earth, suggest that photoperiodism might have evolved before circadian clocks. This is because either long days or long nights are differentially stressful for photoautotrophs like cyanobacteria, and therefore these conditions would be expected to trigger stress responses differentially. As a result of these selective pressures, photoperiodic time measurement might have evolved even before bona fide circadian clocks appeared. ...” ..."

From the editor's summary and abstract:

"Editor’s summary

Long-lived plants and animals clearly regulate their physiology according to seasonal changes in day length to appropriately adjust their physiology. Jabbur et al. found that cyanobacteria can do the same even though individuals only live for a few hours, a time shorter than a single daily photoperiod. Exposure to short photoperiods characteristic of winter stimulated these cyanobacteria to adjust their membrane lipids and gene expression to accommodate cold conditions. These responses required a functional circadian clock. Thus, population-based sensing of photoperiod appears to have evolved early, perhaps as a refinement of stress pathways....

Abstract

Photoperiodic time measurement is the ability of plants and animals to measure differences in day versus night length (photoperiod) and use that information to anticipate critical seasonal transformations, such as annual temperature cycles. This timekeeping phenomenon triggers adaptive responses in higher organisms, such as gonadal stimulation, flowering, and hibernation. Unexpectedly, we observed this capability in cyanobacteria—unicellular prokaryotes with generation times as short as 5 to 6 hours. Cyanobacteria exposed to short, winter-like days developed enhanced resistance to cold mediated by desaturation of membrane lipids and differential programs of gene transcription, including stress response pathways. As in eukaryotes, this photoperiodic timekeeping required an intact circadian clockwork and developed over multiple cycles of photoperiod. Therefore, photoperiodic timekeeping evolved in much simpler organisms than previously appreciated and enabled genetic responses to stresses that recur seasonally."

Researchers Discover the Evolution of Seasonal Anticipation in Cyanobacteria (original news release)

ScienceAdvisor

In a first for microbes, bacteria seem to track—and button up for—the cold

Bacteria can anticipate the seasons: Photoperiodism in cyanobacteria

Lead scientist Maria Luísa Jabbur sitting in front of petri dishes