Humans descended from 'sewage bacteria'

Posted by Emma Woollacott

Oh dear, oh dear. A week or two ago, I found myself on a city street listening to a very cross man on a soap-box explaining that evolutionary theory couldn't possibly be correct, as he remembered his grandfather and his grandfather wasn't a monkey.

Let's just hope this man never sees the latest research from University College Dublin - because a team there has discovered that all multi-celled life on Earth is descended from a type of bacteria now found only in acid bogs and sewage treatment plants.

The bacteria represents a 'missing link' in one of the most important steps in the evolution of life on earth - the emergence of cells with a nucleus containing DNA, known as eukaryotic cells.

For billions of years, bacteria were the only cellular life form on Earth. Then, between about 1.6 and 2.1 billion years ago, eukaryotic cells emerged. These  led to the evolution of all multi-cellular life on earth including plants, insects, animals and humans.

Until now, though, scientists were unable to identify an 'ancestral cell' linking the early prokaryotes with the later eukaryotes. Some suggested that they emerged through fusion, whereby two cells merge to form a new cell.

But the Dublin scientists, along with colleagues from the European Molecular Biology Laboratory in Heidelberg, reckon they've found an intermediate link.

"Our discovery means that the appearance of eukaryotic cells on earth can be explained by Darwinian evolution over billions of years, rather than a 'big bang' fusion theory,” says cell biologist Dr Emmanuel Reynaud from University College Dublin.

"Our analysis shows that PVC [Planctomycetes, Verrucomicrobiae, Chlamydiae] bacteria, members of which are commonly found in today’s sewage treatment plants or acid bogs, represent an intermediate type of cell structure. They are slightly bigger than other known bacteria, and they also divide more slowly."

The implication is that PVC is a descendant of a 'missing link' cell which connected prokaryotic to eukaryotic cells billions of years ago. Our friend on the soap-box may just feel a monkey would be a welcome member of the family in comparison.