Photosynthesis could be as old as life itself

Photosynthesis has been supporting life for longer than previously assumed, according to a new paper. The finding suggests that the earliest bacteria that wiggled their way around the planet were able to perform key processes involved in photosynthesis.

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Exactly how the earliest organisms on our planet lived and evolved is an area of active interest and research — but not answers are few and scarce. However, a new paper could fundamentally change how we think about this process.

The advent of photosynthesis on a large scale is one of the most significant events that shaped life on Earth. Not only did this process feed bacteria and plants that would then support for entire ecosystems, but it also led to a massive increase in atmospheric oxygen levels, basically making our planet livable in the first place. Oxygen that we and other complex life still breathe to this day.

To the best of our understanding , it took life several billion years to evolve the ability to perform photosynthesis. However, if the findings of this new study are confirmed, it means complex life could have appeared much earlier.

A light diet

“We had previously shown that the biological system for performing oxygen-production, known as Photosystem II, was extremely old, but until now we hadn’t been able to place it on the timeline of life’s history. Now, we know that Photosystem II show patterns of evolution that are usually only attributed to the oldest known enzymes, which were crucial for life itself to evolve.”

The team led by researchers from Imperial College London studied the evolutionary process of certain proteins that are crucial for photosynthesis. Their findings show that these could possibly have first appeared in the very early days of life on Earth.

They traced the ‘molecular clock’ of key proteins involved in the splitting of water molecules. This approach looks at the time between ‘evolutionary moments’, events such as the emergence of different groups of cyanobacteria or land plants that carry a version of these proteins. They then used this to calculate the rate at which the proteins evolved over time — by backtracking this rate, researchers can estimate when a protein first appeared.

A comparison with other known proteins, including some used in genetic data manipulation that should (in theory) be older than life itself, as well as comparison with more recent events, suggests that these photosynthesizing enzymes are very old. According to the team, they have nearly identical patterns of evolution to the oldest enzymes — suggesting they evolved at a similar rate for a similar time.

Based on what we know so far, type II photosynthesis (which produces oxygen) likely appeared around 2.5 billion years ago in cyanobacteria (blue-green algae), with type I likely evolving some time before that. But there’s something that doesn’t really mesh with that timeframe: we know that there were pockets of atmospheric oxygen before this time. This means that biological communities were around to produce said oxygen even before the 2.5 billion years ago mark, since oxygen is extremely reactive and doesn’t last long in nature without binding to something. Researchers have been trying to reconcyle this for a while.

The current findings could help make everything fit. According to the team, key enzymes that underpin photosynthesis were likely present in the earliest bacteria on Earth. There’s still some uncertainty about this, as life on our planet is at least 3.4 billion years old, but it could be older than 4 billion years.

The first versions of the process were probably simplified, very inefficient versions of the one seen in plants and algae today. It took biology around one billion years to tweak and refine the process, which eventually led to the appearance of cyanobacteria. From there, it took two more billion years for plants and animals to colonize dry land, with the latter breathing oxygen produced by the former.

One interesting implication of these findings is that it could mean life would evolve much quicker and easier on other planets than previously assumed. We tend to estimate this based on how quickly and easily life appeared and then developed on Earth.

The paper “Time-resolved comparative molecular evolution of oxygenic photosynthesis” has been published in the journal Biochimica et Biophysica Acta (BBA) – Bioenergetics.

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