We may Need to Rethink Everything We Thought We Know About the Origins of Photosynthesis

Structures revealed within strange bacteria are similar to those that enhance photosynthesis in current plants, indicating that the process may be much older than currently accepted.

And that’s kind of a big deal.

As revealed by scientists, the finding could mean that the evolution of photosynthesis needs a rethinking, making traditional ideas obsolete.

Photosynthesis is defined as the ability to use the sun’s energy to produce sugars through chemical reactions. Plants, algae and some bacteria today perform ‘oxygenated’ photosynthesis, which divides water into oxygen and hydrogen to boost the process, releasing oxygen as a waste product; a wonder of evolution.

However, some bacteria, on the other hand, perform ‘anoxygenic’ photosynthesis, a version that uses molecules other than water to boost the process and does not release oxygen.

Scientists have assumed that anoxygenic photosynthesis is more “primitive,” and that oxygenic photosynthesis evolved from it.

Under this point of view, anoxygenic photosynthesis arose about 3.5 billion years ago and oxygenic photosynthesis developed a billion years later.

But the timeline may all be wrong.

After studying structures within an ancient type of bacteria, researchers at Imperial College London have suggested that a key step in oxygenic photosynthesis could have already been possible one billion years earlier than previously thought.

The lead author of the study, Tanai Cardona, of the Department of Life Sciences at Imperial, explained that only known are we beginning to see that much of the history established about the evolution of photosynthesis is not supported by the actual data we obtain on the structure and functioning of the first bacterial photosynthesis systems.

The bacteria scientists studied, Heliobacterium modesticaldum, is found around hot springs, soils and flooded fields, where it performs anoxygenic photosynthesis. It is closely related to cyanobacteria, the main bacterium that performs oxygenic photosynthesis today.

This is so distantly related that it had for the last time a “common ancestor” with cyanobacteria billions of years ago.

What this means is that any trait that the two bacteria share has probably also been present in the ancient bacteria that gave rise to both.

After analyzing the structures that both H. modesticaldum and modern cyanobacteria use to perform their different types of photosynthesis, Cardona found surprising similarities.

Researchers discovered how both structures contain a feature that cyanobacteria and plants use exclusively to divide water, the first crucial step for oxygenic photosynthesis.

Scientists often have assumed that the evolution of cyanobacteria is also the first occurrence of oxygenated photosynthesis, but the fact that H. modesticaldum holds a similar feature means that the basic components for oxygenated photosynthesis are likely to be much older than previously thought, perhaps as old as photosynthesis itself, and therefore may have originated much earlier in Earth’s history.

This could mean that oxygenic photosynthesis was not the product of a billion years of evolution from anoxygenic photosynthesis, but that it could have been a feature that evolved much earlier, if not first.

The results of the study, published in Trends in Plant Science, helps explain why the systems responsible for photosynthesis and oxygen production are the way they are today, but to make sense, a change in perspective is required in the way we see the evolution of photosynthesis.

The study explains that under the traditional point of view, anoxygenic photosynthesis evolved first and was the only type for approximately one billion years or more before the evolution of oxygen photosynthesis.

This means that these structures should not exist at all in this type of bacteria.

Ready to rethink our views on evolution? This is the first step.

Science DirectImperial College London
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