Irish scientist helps unscramble life's complex origins

A MAYNOOTH scientist has made a major breakthrough in understanding how complex life on Earth originated.

It is known from fossil records that life on Earth began about three billion years ago, but for the first billion years only single-celled organisms existed.

The process by which those organisms became multi-celled organisms such as plants and animals, including humans, is one of the great questions of science, along with the origins of life itself.

All multi-celled organisms and some unicellular organisms are distinguished by having a nucleus that contains their genetic material for reproduction.

That makes them eukaryotes and all the DNA is contained in the nuclei. Without a nucleus, complex life cannot evolve.

Dr James McInerney of NUI Maynooth’s bioinformatics and molecular evolution unit of the department of biology said the original eukaryote was a single-celled organism with a nucleus that originated when two prokaryotes, single-celled organisms without nuclei, combined.

One was a eubacterium, the most common form of bacterium; the other was from the relatively less plentiful archaebacteria, also known as extremophiles, which can thrive in places hostile to all other forms of life. Both types of bacterium are very different.

Dr McInerney said this event, without which complex life on earth would not have evolved, happened only once.

“There was a big transition from these tiny little single-celled organisms to something that could get big. It seems like two billion years ago this kind of event happened. We have been interested in finding out how exactly it happens,” he said.

The research was carried out in conjunction with the Sanger Institute in Cambridge and the results were published in the prestigious American scientific journal The Proceedings of the National Academy of Sciences this week.

Dr McInerney said they had been able to carry out the research because the genome (the entire DNA sequence) of everything from humans to yeast had been mapped.

Using baker’s yeast as a representative of the eukaryotes, they were able to find some genes within yeast that were closely related to eubacteria and others to archaebacteria.

“We have some evidence that two different organisms came together to form the eukaryotes. The paper we have published is a sort of a deeper analysis of the biochemistry and genetics of yeast,” he said.

Ken Wolfe, professor of genome evolution at the Smurfit Institute of Genetics, Trinity College Dublin, praised the research.

He said the idea that complex life originated from a single event when a eubacterium and an archaebacterium combined was not new, but the researchers had taken it further by demonstrating the manner in which the genes from both parent species had contributed to the new hybrid organism.

He said that though the genes from the eubacteria were three times more prevalent in yeast than the archaebacteria, the archaebacterial genes were more important.

Prof Wolfe explained: “If you try to knock out those genes [the archaebacterium] in yeast, they often turn out to be essential for life.

“In contrast, the yeast genes that were derived from the eubacterium are more peripheral and often are not essential.

“Dr McInerney’s work suggests that the archaebacterium was in the driving seat when the two cells merged, even though it contributed fewer genes.”