Biochemical controls: predicting seasonal change (Introduction)

by David Turell , Saturday, October 12, 2024, 20:09 (40 days ago) @ David Turell

Bacteria do it:

https://www.quantamagazine.org/even-a-single-bacterial-cell-can-sense-the-seasons-chang...

"Every year, in latitudes far enough north or south, a huge swath of life on Earth senses that winter is coming. Leaves fall from trees, sparrows fly to the tropics, raccoons grow thick winter coats, and we unpack our sweaters from storage. Now scientists have shown that this ability to anticipate shorter days and colder temperatures is more fundamental to life than anyone thought: Even short-lived, single-celled organisms can sense day length and get themselves ready for winter.

"Lab experiments, recently published in Science, show that cyanobacteria — a type of bacteria that produces energy from sunlight through photosynthesis — anticipate the change(opens a new tab) by bundling up in their own way. They turn on a set of seasonal genes, including some that adjust the molecular composition of their cell membranes, to improve their odds of survival.

"The study authors were amazed to find this season-sensing ability in an organism that lives for only about five hours in the lab before dividing. “It seemed like a very nonsensical idea to think that bacteria would care about something that’s happening on a scale that’s so much bigger than their lifetime,” said Luísa Jabbur, a microbial chronobiologist.

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“'This issue of dealing with seasonality may be very fundamental to why [biological] clocks exist in the first place,” said the cell biologist Mike Rust(opens a new tab), who studies cyanobacteria’s internal rhythms at the University of Chicago and was not involved in the new research. Staying in sync with the seasons could be more ancient and more elemental to life than anyone suspected.

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"...in 1986, evidence emerged that cyanobacteria do indeed have daily rhythms. When the South African plant physiologist Nathanaël Grobbelaar exposed cyanobacteria to light and dark periods, he observed that the cells processed nitrogen, a key nutrient, only during the simulated night(opens a new tab). It was the first record of a day-night internal rhythm in any single-celled organism.

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"In papers published in 1993(opens a new tab) and 1998(opens a new tab), with collaborators in Japan and Texas, he identified three genes and their corresponding proteins — KaiA, KaiB and KaiC (kai is Japanese for “cycle”) — involved with the cyanobacterial circadian clock. Interactions between KaiA and KaiB create a reaction in which KaiC acquires an extra phosphate group and then sheds it rhythmically, in sync with day and night. Astonishingly, the scientists also found that the whole loop can happen outside a cell, among loose molecules in a test tube.

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"It is well known that cell membranes, including those that encircle cyanobacteria, are sensitive to temperature. Like butter, the lipids that compose membranes become more rigid in cold conditions and more fluid in heat. Many organisms can adjust their membranes — a process known as desaturation — to keep molecules moving freely across the membrane in a range of temperatures. Jabbur wondered if her cyanobacteria were doing the same thing. Indeed, further experiments showed that her winter-primed cyanobacteria had more desaturated lipids that kept their cell membranes from gumming up as the temperature dropped.

"Finally, she wanted to know if these photoperiodic adaptations were tied to the circadian clock or driven by a separate mechanism. When the researchers deleted the genes that encode the KaiA, KaiB and KaiC proteins, the winter-condition cells survived no better than summer-condition cells. They had failed to adjust their lipids. The daily molecular clock might be driving the seasonal calendar as well.

“'We still don’t know if the clock is the one that is actually encoding the day length,” Jabbur said. “But it appears to be necessary for the response.”

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“'It is truthfully impressive that organisms as old as cyanobacteria could have this kind of response,” Jabbur said. “It makes one really wonder about when [photoperiodism] first emerged, and what Earth looked like back then.”

"Because organisms go through daily cycles more frequently than seasonal ones, scientists have generally assumed that circadian clocks evolved before photoperiodism. But the new research suggests another possibility. “Photoperiodic measurement could have been the first thing [to evolve],” Johnson said. Perhaps our oldest ancestors needed to invent an internal clock to survive the stresses of seasonal weather — and then daily cycles were built on top of that."

Comment: the anticipation of environmental change is a conceptual idea. Not something a set of cells could anticipate. Pure evidence for design.