An ancient form of photosynthesis was apparently far more common on early Earth than researchers first believed, as scientists in London have discovered that a more primitive form of the process in ancient bacteria evolved more than 3.5 billion years ago.
Photosynthesis is the process that helps sustain life on Earth by absorbing sunlight and carbon dioxide before releasing oxygen into the atmosphere. This form of oxygen-producing photosynthesis allowed complex life forms to evolve.
The more ancient form of photosynthesis, called anoxygenic photosynthesis, didn't produce oxygen. When it first evolved in an ancient bacterium, it took in sunlight but didn't release this gas. It was passed on to other bacteria with the help of horizontal gene transfer, which is when an organism donates an entire set of genes to unrelated organisms.
In order to find the origin of anoxygentic photosynthesis, the researchers traced the evolution of BchF, which is a protein that's key in the biosynthesis of bacteriochlorophyll a. This is the main pigment that's used in anoxygenic photosynthesis. By comparing sequences of proteins and reconstructing an evolutionary tree, researchers found that it originated before most modern groups of bacteria that are living today.
"The picture that is starting to emerge is that during the first half of Earth's history the majority of life forms were probably capable of photosynthesis," Tanai Cardona from the Department of Life Sciences at Imperial Collect London said. "Pretty much every group of photosynthetic bacteria we know of has been suggested, at some point or other, to be the first innovators of photosynthesis. But this means that all these groups of bacteria would have to have branched off from each other before anoxygenic photosynthesis evolved, around 3.5 billion years ago."
Instead, the researchers found that anoxygentici photosynthesis actually predates the diversification of bacteria into modern groups. This means that all bacteria, at the time, should have been able to accomplish this feat. The evolution of photosynthesis that produced oxygen is what probably caused many groups of bacteria who could do the more ancient form of photosynthesis to become extinct.
The findings reveal a bit more about these ancient groups. More specifically, they show how these ancient bacteria may have evolved over time.
The study was published in the March 8 issue of the journal PLOS ONE.
