Uprooting and replanting the tree of life

A new theory on the evolution of ancient microbes is set to challenge widespread scientific views of early life on earth and could overturn previous interpretations of the huge bank of molecular taxonomic data that has been built up in recent years, according to research published today in the International Journal of Systematic and Evolutionary Microbiology.

“I`ve reinterpreted fossil records to show that eukaryotes, which includes plants, animals and fungi, are only half as old as previously thought and are quite closely related to a group of micro-organisms called archaebacteria. Archaebacteria therefore are also younger than they are usually thought,” says Professor Tom Cavalier-Smith of Oxford University.

It is currently accepted that there are three branches to the tree of life: bacteria (as we know them), eukaryotes and archaebacteria. Bacteria evolved 3500-3850 million years ago. Archaebacteria were also believed to be ancient because of their unusual cell structure.

But Prof Cavalier-Smith argues, “This research shows that archaebacteria and eukaryotes should be placed together in one big group called neomura, which means new walls. These organisms have a common ancestor that evolved 850 million years ago to contain a substance called glycoprotein in its membrane, which gave it greater fluidity than the rigid cell walls of ordinary bacteria.”

“The unusual cell structure of archaebacteria can be explained as relatively recent adaptations to life in extreme environments such as boiling water and hot acid. Many changes occurred in proteins that help to stabilise DNA such as histone proteins and ribosomes. These adaptations vastly accelerated the evolutionary rate of the molecules concerned, and implies that current estimates of age based on molecular data are hugely distorted,” explains Prof Cavalier-Smith.

“The neomuran ancestor has been identified as an actinobacterium, which is related to the bacteria that cause tuberculosis and leprosy. It is intriguing to think that we are more closely related to tuberculosis bacteria than they are to E. coli,” says Prof Cavalier-Smith.