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Scientists demonstrate that a key organism in the ocean’s food web will begin reproducing at high speed as carbon dioxide levels rise, with no way to stop when nutrients become scarce

Imagine being in a car with the gas pedal stuck to the floor, heading toward a cliff’s edge. Metaphorically speaking, that’s what climate switch will do to the key group of ocean bacteria known as Trichodesmium, scientists have discovered.

Trichodesmium (called “Tricho” for brief by researchers) is one of the few organisms in the ocean that can “fix” atmospheric nitrogen gas, making it available to other organisms. It is crucial because all life — from algae to whales — needs nitrogen to grow.

A fresh investigate from USC and the Massachusetts-based Forest Crevice Oceanographic Institution (WHOI) shows that switching conditions due to climate switch could send Tricho into overdrive with no way to stop — reproducing quicker and generating lots more nitrogen. Without the capability to slow down, however, Tricho has the potential to gobble up all its available resources, which could trigger die-offs of the microorganism and the higher organisms that depend on it.

Amped-up bacteria

By breeding hundreds of generations of the bacteria over the course of almost five years in high-carbon dioxide ocean conditions predicted for the year 2100, researchers found that enlargened ocean acidification evolved Tricho to work tighter, producing fifty percent more nitrogen, and grow swifter.

The problem is that these amped-up bacteria can’t turn it off even when they are placed in conditions with less carbon dioxide. Further, the adaptation can’t be reversed over time — something not seen before by evolutionary biologists, and worrisome to marine biologists, according to David Hutchins, lead author of the examine.

“Losing the capability to regulate your growth rate is not a healthy thing,” said Hutchins, professor at the USC Dornsife College of Letters, Arts and Sciences. “The last thing you want is to be stuck with these high growth rates when there aren’t enough nutrients to go around. It’s a losing strategy in the fight to sustain.”

Tricho needs phosphorous and metal, which also exist in the ocean in limited supply. With no way to regulate its growth, the turbo-boosted Tricho could burn through all of its available nutrients too quickly and abruptly die off, which would be catastrophic for all other life forms in the ocean that need the nitrogen it would have produced to sustain.

Some models predict that enhancing ocean acidification will exacerbate the problem of nutrient scarcity by enhancing stratification of the ocean — locking key nutrients away from the organisms that need them to get through.

What the future may hold

Hutchins is collaborating with Eric Webb of USC Dornsife and Mak Saito of WHOI to build up a better understanding of what the future ocean will look like, as it resumes to be shaped by climate switch. They were shocked by the discovery of an evolutionary switch that shows up to be permanent — something Hutchins described as “unprecedented.”

The evolutionary biologists are interested in it just to probe this as a basic evolutionary principle.

“Tricho has been studied for ages. Nobody expected that it could do something so bizarre,” he said. “The evolutionary biologists are interested in it just to examine this as a basic evolutionary principle.”

The team is now studying the DNA of Tricho to attempt to find out how and why the irreversible evolution occurs. Earlier this year, research led by Webb found that the organism’s DNA inexplicably contains elements that are usually only seen in higher life forms.

“Our results in this and the aforementioned probe are truly surprising. Furthermore, they are providing us an improved view of how global climate switch will influence Trichodesmium and the vital supplies of fresh nitrogen it provides to the rest of the marine food web in the future.” Webb said.

Hutchins, Webb and Saito collaborated with Nathan Walworth, Jasmine Gale and Fei-Xue Fu of USC; and Dawn Moran and Matthew McIlvin of WHOI. The work was funded by the National Science Foundation (grants OCE 1260490, OCE 1143760, OCE one million two hundred sixty thousand two hundred thirty three and OCE OA 1220484); and the G.B. Moore Foundation (grants three thousand seven hundred eighty two and 3934).

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