New research has shown that a group of bacteria that survive due to chemical reactions caused by
"The discovery shows that we must beare careful when making assumptions about the rate of evolution and how we interpret the tree of life, said Eric Beckcraft, lead author of the paper. “This will make it difficult to establish reliable molecular timelines.”
Becraft, now an assistant professor of biology at the University of North Alabama, completed the research as part of his doctoral work in Bigelow's lab and recently published it in the journalISMEpublishing group Nature.
Candidatus Desulforudis audaxviator bacteriafirst discovered in 2008 by a group of scientists led by Tallis Onstott, co-author of a new study. They were found in a South African gold mine almost two miles from the surface of the Earth. There they receive the energy they need as a result of chemical reactions caused by the natural radioactive decay of minerals. They live in water-filled cavities inside rocks in a completely independent ecosystem, free from sunlight or any other organisms.
Due to their unique biology and isolation, the authorsnew research wanted to understand how bacteria evolved. They examined other environmental samples deep underground and found Candidatus Desulforudis audaxviator in Siberia and Death Valley in California, as well as in several mines in South Africa. Each environment was chemically different. This gave scientists a unique opportunity to look for differences that have arisen between populations over millions of years of their evolution.
Equipment for underground sampling of microbesstands in Death Valley, California. A new study by the Bigelow Ocean Science Laboratory has shown that a group of microbes, Candidatus Desulforudis audaxviator, have been in evolutionary stagnation for millions of years. Credit: Dwayne Moser, Institute for Desert Research.
"We wanted to use this informationto understand how they evolved and what environmental conditions lead to which genetic adaptations, explains Ramunas Stepanauskas, a senior researcher at the Bigelow Laboratory and author of the paper. “We thought of bacteria as if they were isolated island dwellers, like the finches Darwin studied in the Galapagos Islands.”
Using advanced tools, the researchers examined the genomes of 126 bacteria sourced from three continents. Surprisingly, they all turned out to be almost identical.
Scientists have found no evidence that microbescan travel long distances, survive on the surface, or live long in the presence of oxygen. So, once the researchers determined that there was no possibility of cross-contamination of the samples during the study, there were fewer plausible explanations.
"The best explanation we have"for now, is that these microbes haven't changed much since they moved during the breakup of the supercontinent Pangea about 175 million years ago," Stepanauskas concludes. “They seem like living fossils from those days.” This sounds pretty crazy and contradicts modern understanding of bacterial evolution."
Many well-studied bacteria, such as E. coli, evolve in just a few years in response to environmental changes such as exposure to antibiotics.
Stepanauskas and his colleagues suggest that the quiescent evolution they discovered is due to the microbes' powerful defense against mutation, which essentially locked their genetic code.
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