Microbes played key role in developing modern nitrogen cycle 2.5 billion years ago

February 20th, 2009 - 3:52 pm ICT by ANI  

Washington, Feb 20 (ANI): A new research has shown that for the countless billions of tiny microbes, large-scale evolution was completed 2.5 billion years ago, and they played a key role in developing modern nitrogen cycle.

For microbes, it appears that almost all of their major evolution took place before we have any record of them, way back in the dark mists of prehistory, said Roger Buick, a University of Washington paleontologist and astrobiologist.

All living organisms need nitrogen, a basic component of amino acids and proteins. But for atmospheric nitrogen to be usable, it must be fixed, or converted to a biologically useful form.

Some microbes turn atmospheric nitrogen into ammonia, a form in which the nitrogen can be easily absorbed by other organisms.

But, the new research shows that about 2.5 billion years ago, some microbes evolved that could carry the process a step further, adding oxygen to the ammonia to produce nitrate, which also can be used by organisms.

That was the beginning of what today is known as the aerobic nitrogen cycle.

The microbes that accomplished that feat are on the last, or terminal, branches of the bacteria and archaea domains of the so-called tree of life, and they are the only microbes capable of carrying out the step of adding oxygen to ammonia.

The fact that they are on those terminal branches indicates that large-scale evolution of bacteria and archaea was complete about 2.5 billion years ago, according to Buick, a UW professor of Earth and space sciences.

Countless bacteria and archaea species have evolved since then, but the major branches have held, he said.

The scientists examined material from a half-mile-deep core drilled in the Pilbara region of northwest Australia.

They looked specifically at a section of shale from 300 to 650 feet deep, deposited 2.5 billion years ago, and found telltale isotope signatures created in the process of denitrification, the removal of oxygen from nitrate.

If denitrification was occurring, then nitrification the addition of oxygen to ammonia to form nitrate also must have been taking place, Buick said.

That makes the find the earliest solid evidence for the beginning of the aerobic nitrogen cycle.

What this shale deposit has done is record the onset of the modern nitrogen cycle, said Buick. This was a life-giving nutrient then and remains so today, he added.

According to the researchers, it seems clear that the tiniest creatures played a crucial role in completing the nitrogen cycle that life depends on today. (ANI)

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