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Discovery in living fossil hints at earliest origins of life

Discovery in living fossil hints at earliest origins of life

By David Self Newlin | Posted - Nov. 19, 2012 at 12:03 p.m.



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JACKSON HOLE — Scientists have found a chemical, previously unknown in nature, in an ancient form of bacteria that could indicate how genetic information was transferred in the very earliest forms of life, before the DNA and RNA now found in all living things even existed.

In Jackson Hole, Wyoming, a team of scientists from the Institute for Ethnomedicine and have been studying photosynthetic cyanobacteria in the search to understand neurodegenerative diseases.

These bacteria are extremely ancient and are the oldest form of photosynthesizing organism. They live everywhere, all around us. The form pond scum and algal blooms and are found even in the most extreme heat and cold. They're also thought to have been responsible for creating Earth's first atmosphere with oxygen in it, a key event in Earth's history.

While studying cyanobacteria, the researchers discovered something entirely unexpected. It's called N-(2-Aminoethyl)glycine, or AEG for short. It's been used by the pharmaceutical industry to build what you might call synthetic genetic information, and it's been proposed as the basis of a very simple form of genetic information that could have existed before DNA- or RNA-based life.

Basically, deoxyribose forms the backbone of DNA, and bases like adenine or guanine attach themselves to it in specific orders to create genes. But it is possible to use AEG to form a backbone as well, and in fact if you do that, the whole chain is much simpler and more stable than DNA could ever be.

The structure of AEG in a polymer.
The structure of AEG in a polymer.

"People were trying to work out how to alter the expression of genes in cells and in environments, so they decided that rather than making a molecule like DNA, they wanted to make something that's pretty simple," said visiting researcher Dr. James Metcalf.

Its simplicity and stability make it appealing in theorizing that that it could have been an early form of genetic material. But there was a problem: AEG had only been seen inside the lab and it had never been found in nature before. That is, until turned up in their samples of cyanobacteria.

To take things further, the team then looked at samples of cyanobacteria from around the world, which turned out to have AEG as well. Colleagues at Stockholm University found identical results.

The findings have serious implications. It's almost a double whammy: Not only was it found in nature for the first time, it was found in one of the most ancient organisms known, essentially a living fossil.

That could indicate a number of things, the most interesting which is that it is a remnant of an older gene system that still functions alongside the DNA-based system found inside the bacteria, according to institute Director Dr. Paul Cox.

"Maybe there's some connection between primitive genic systems and the presence of AEG," Cox said.

It's a long shot, but it's intriguing enough to follow up on. Banack, Metcalf and Cox will soon design experiments to figure out how the AEG is produced and what it is used for.

Dr. Cox has previously done work on pond scum, a kind of cyanobacteria, theorizing that a neurotoxin known as BMAA causes some common disorders like Alzheimer's.

It turns out that AEG has the same molecular weight as BMAA. That allowed the team to take notice and perform a more extensive search to determine exactly what they had found, according to Senior Scientist and lead author Dr. Sandra Banack.

A paper on their findings has been published in the journal PLoS One.

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David Self Newlin

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