Recreating 3.5 billion year-old genes
A U.S. team of scientists wanted to determine what was the Earth's temperature several billions years ago. But because most of the team was composed of biologists, the researchers took an unusual approach. Instead of analyzing rock formations or measuring isotopes in fossils, they've 'resurrected' a variety of genes and proteins that existed several billion years ago. And they found that 'the Earth endured a massive cooling period between 500 million and 3.5 billion years ago,' a result in full agreement with previous to geologic studies. They say that even if the Earth was very hot in the beginning, the environment cooled progressively by 30 °C during 3 billion years. But read more...
This scientific team was led by Eric Gaucher, president of scientific research at the Foundation for Applied Molecular Evolution (FFAME). For this project, he worked with Omjoy Ganesh, a structural biologist at the University of Florida and with Sridhar Govindarajan, vice president of informatics at DNA2.0, a California-based company that constructed the genes.
[Note: Can you believe that this company chose a name like DNA2.0? Even if it's a real company, with real products, and which can build genes for you, what do you think of that name?]
Anyway, here is a quote from Eric Gaucher about this project. "By studying proteins encoded by these primordial genes, we are able to infer information about the environmental conditions of the early Earth. Genes evolve to adapt to the environmental conditions in which an organism lives. Resurrecting these since long-extinct genes gives us the opportunity to analyze and dissect the ancient surroundings that have been recorded in the gene sequence. The genes essentially behave as dynamic fossils."
Personally, I like this idea of "dynamic fossils." But it's only an expression. So what did the scientists really achieve? "After scanning multiple databases, the scientists struck gold with a protein called elongation factor, which helps bacteria string together amino acids to form other proteins. Each bacterial species has a slightly different form of the protein: Bacteria that live in warmer environments have resilient elongation factors, which can withstand high temperatures without melting. The opposite is true for bacteria that live in cold environments. Armed with information about when bacterial species evolved, the scientists rebuilt 31 elongation factors from 16 ancient species. By comparing the heat sensitivity of the reconstructed proteins, they were able to discern how Earth’s temperature changed over the ages."
This research work has just been published in Nature under the title "Palaeotemperature trend for Precambrian life inferred from resurrected proteins" (Volume 451, Number 7179, Pages 704-708, February 7, 2008). Here is a link to the editor's summary, Time travelling proteins. "Comparisons of genome sequence data in closely and distantly related modern organisms can be used for the computational reconstruction of ancient protein sequences that may have existed in related but now extinct types. These proteins can then be 'resurrected' in the laboratory. This has now been achieved for a group of 25 ancestral elongation factors from bacteria across an estimated span of 3 billion years. These ancient proteins display a near linear increase in thermostability travelling back in geological time, suggesting that the environment supporting ancient life was initially hot, then cooled progressively by about 30 °C during that period. This pattern is corroborated by the palaeotemperature trend inferred for the geologic record."
And here are some excerpts from the abstract of this article. "Biosignatures and structures in the geological record indicate that microbial life has inhabited Earth for the past 3.5 billion years or so. [...] Only recently have the natural sciences been able to provide experimental results describing the environments of ancient life. Our previous work with resurrected proteins indicated that ancient life lived in a hot environment. [...] Here we show that our results are robust to potential statistical bias associated with the posterior distribution of inferred character states, phylogenetic ambiguity, and uncertainties in the amino-acid equilibrium frequencies used by evolutionary models. Our results are further supported by a nearly identical cooling trend for the ancient ocean as inferred from the deposition of oxygen isotopes."
Sources: University of Florida news release, via EurekAlert!, February 7, 2008; and various websites
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