New research has identified what were probably the smallest living fossils to date – a group of microbes that feed on radioactive decay.
The team, led by the Bigelow Laboratory of Ocean Sciences, an independent non-profit oceanography research institute, reports that the microbes have been frozen for millions of years, evolutionarily. If we find such a case, it could help our current understanding of how microbes develop and why it does, and could possibly help guide biotechnology applications in the future (since you want it not to evolve / change over time ).
We’re fine as we are
“This discovery shows that we need to be careful when making assumptions about the speed of evolution and how we interpret the tree of life,” said Eric Becraft, the paper’s lead author. “It is possible that some organisms have an evolutionary full sprint, while others are slow to crawl, challenging the establishment of reliable molecular timelines.”
The microbial species is known as Candidatus Desulforudis audaxviator, and was first discovered in 2008 by a group of researchers led by Tullis Onstott, a co-author of the new study. They live in a gold mine in South Africa, almost two kilometers below the surface, and swim merrily in the water-filled cavities within the rock walls. They feed on chemical products formed by natural radioactive decay processes in on-site minerals, creating a completely independent ecosystem that does not even rely on sunlight to function.
Because of their very peculiar life arrangement, the team understandably wanted to know how the microbes evolved to where they are today. They examined other subterranean monsters found around the world and found the species in Siberia, California, and in several other mines in South Africa. Each of these environments was chemically different, the team explains, prompting them to look for differences between the population at each site. These groups were obviously separated and were probably separate for millions of years, and each had unique conditions in which they lived – which would make you think that they had developed their own unique characteristics.
“We wanted to use the information to understand how they develop and what kind of environmental conditions lead to what kind of genetic adaptations,” said Bigunow Laboratory research scientist Ramunas Stepanauskas.
“We thought of the microbes as if they were inhabitants of isolated islands, like the finches that Darwin studied in the Galapagos.”
Therefore, they analyzed the genetic code of 126 individuals found at sites on three different continents – and they were surprised to discover that they were all almost identical.
They ruled out the possibility that these microbes could have traveled between the sites. The species is anaerobic and cannot live long in the presence of oxygen; they do not survive well on the surface; the team also ruled out cross-contamination between these sites.
The best explanation they have so far, the team explains, is that these communities have not changed so much genetically since they were first separated about 175 million years ago when the supercontinent Pangea was divided. In essence, they are living fossils.
‘They seem to have been living fossils since that time. It sounds quite crazy and goes against the modern concept of microbial evolution, ”says Stepanauskas.
The findings provide a unique counterpoint to the much faster rate of mutation and evolution seen in other microbial communities. It has been observed that populations of bacteria such as E. coli develop within a few years (in response to environmental changes). The growing problem of antibiotic resistance is an example of how quickly bacteria can develop.
The current hypothesis of the team is that the genetic freezing of the species is due to powerful antimutational mechanisms in its genome. We do not yet know if this is true, but if it is, we could discover an extremely rare feature that we can copy and exploit. Developing this into an instrument could pave the way for more stable DNA polymerases (molecules that copy DNA strands), which is an important component of our biotechnology kit. In essence, it will allow us to make the biological machinery that copies DNA much more stable over time, which sounds unimpressive, but is actually a very big deal for the field.
But the findings also have profound implications for how we think about microbial genetics and the rate at which such microscopic organisms mutate.
“There is a huge demand for DNA polymerases that do not make many errors,” Stepanauskas said. “Such enzymes can be useful for DNA sequencing, diagnostic tests and gene therapy.”
“These findings are a powerful reminder that the different microbial branches we observe on the tree of life can differ greatly in the time since their last common ancestor,” Becraft said. “Understanding this is critical to understanding the history of life on earth.”
The article “Evolutionary stasis of a deep subsurface microbial lineage” was published in The ISME Journal.