Primitive microbes stole bacterial genes on a surprising scale

October 16, 2014, University of Otago
Primitive microbes stole bacterial genes on a surprising scale
In the late 1970s, the hot springs of Yellowstone National Park were among the first places that Archaea, a previously unsuspected domain of life, were discovered.

A University of Otago researcher is part of an international team that has discovered that horizontal gene transfer (HGT) played a surprisingly large role in the evolution of primitive microbes known as archaea.

HGT, which involves acquiring genetic material from another unrelated organism instead of inheriting it from a direct ancestor, is most known today for its role in antibiotic resistance and its use in genetic modification technologies.

The team's findings appear this week in the prestigious journal Nature and show that have swiped dozens, and sometimes hundreds, of on numerous occasions. Their research shows that these gene transfers are a far more important mechanism of than had been previously thought.

Archaea, which live in environments ranging from boiling geysers to the human navel, are single-celled microbes representing one of the three domains of life. The other two are bacteria and eukaryotes (organisms whose cells have a nucleus, such as plants and animals).

The study was led by Dr Shijulal Nelson-Sathi and Professor Bill Martin of Heinrich Heine University in Dusseldorf in collaboration with scientists from the University of Kiel, Germany and the National University of Ireland, and Otago researcher Associate Professor David Bryant.

The team used massive computer clusters to study the evolutionary history of the genes in higher archaea. They compared 267,568 protein-coding genes of 134 sequenced archaeal genomes with the equivalent genes from 1,847 bacterial genomes and established their evolutionary relationships.

The origins of 13 groups of higher archaea were unexpectedly found to correspond to 2,264 group-specific gene acquisitions from bacteria.

Many of taken were those involved in metabolic functions. For example, several groups of archaea whose ancestors used inorganic compounds to generate energy were now able to switch to using organic compounds and thus live in different environments.

Dr Bryant of Otago's Department of Mathematics and Statistics helped design novel statistical tests for the study.

"These results shift the balance in our ideas about microbial evolution. We had known about these for some time. What we didn't appreciate was how they were responsible for such a huge part of microbial evolution," he says.

Explore further: New database provides vast trove of genetic information on tiny single-celled organisms in the ocean

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5 / 5 (1) Oct 16, 2014
Interesting results of course. But the press release is steeped in mistakes. Stem archaea aren't "primitive" of course, they have evolved as much as all other species. But they are not so derived, meaning they split earlier from the bacterial root. Likewise crown archaea aren't "higher", just later splits.

As for HGT as opposed to VGT, the former is ~ 1 HGT event/gene while the latter is 1 VGT/generation, so a relative frequency of HGT of ~ 1/4*10^10 or so. [Um, ref. Koonin et al IIRC.] That is despite that bacteria and archaea uses plasmids for directed HGT such as those pesky antibacterial resistance genes. But when it is fixated, it is a significant factor in acquiring new traits.
5 / 5 (1) Oct 16, 2014
Stem archaea aren't "primitive" of course, they have evolved as much as all other species. But they are not so derived, meaning they split earlier from the bacterial root. Likewise crown archaea aren't "higher", just later splits.

Sulfolobus acidocaldarius, an archaeon, was measured as having the lowest spontaneous mutation rate (per genome, not per base pair) of any microbe and many archaea are slow growing (long generation times). This species has also been noted for being unable to propagate the viruses and plasmids found in other Sulfolobus. There is no universal evolution rate and some species have not evolved as much as other species.
5 / 5 (1) Oct 17, 2014
Agreed, no universal rate, meaning the old notions of "primitive" and "higher" is even more ludicrous than looking at the total evolutionary process time as (more or less useful) proxy.

"In the light of the foregoing examples, it should be clear why there has long been a tendency to avoid description of particular species or traits in terms such as primitive. The word may seem convenient, but it confuses concepts that need separate consideration. ,,, Evolutionary biologists hardly use the term primitive; many current textbooks do not mention it at all. ... Possibly popular writings have been the main reason of the prominence of the word; ... _ an unacceptable nuisance_". [My underscore]

[ http://en.wikiped...enetics) ]

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