Scientists collect samples in Death Valley National Park. The researchers analyzed thousands of microbial genomes and discovered that two common groups produce energy using ancient methods that may predate the development of breathing. Photo credit: Ramunas Stepanauskas
Researchers analyze thousands of microbial genomes and discover that two common groups produce energy using ancient methods that may predate the development of breathing.
A new scientific study has revealed unique life strategies of two main groups of microbes that live beneath the earth’s surface. A publication in Limits in Microbiology reports that these groups, originally believed to be based on symbiotic relationships with other organisms, may also live independently, using an ancient way of producing energy.
“These microbes, belonging to the Patescibacteria and DPANN groups, are really special, really exciting examples of early life,” said Ramunas Stepanauskas, senior scientist at the Bigelow Laboratory for Ocean Sciences and author of the paper. “They could be remnants of ancient life forms that have been hiding and thriving underground for billions of years.”
Stepanauskas led a research team that used advanced molecular techniques and bioinformatics to analyze thousands of microbial genomes and learn about their evolutionary history. Reading their genetic code revealed that these two groups of abundant microbes cannot breathe to synthesize ATP, the common energy currency of life.
The team found that these microbes, who live in a variety of environments inside the Earth, appear to gain energy only through the fermentation process. Many organisms are capable of fermentation, including humans, when their muscles run out of oxygen during intense exercise – but they only use it as an extra source of energy.
“Our results show that Patescibacteria and DPANN are ancient life forms that may never have learned how to breathe,” said Stepanauskas. “These two major branches of the evolutionary tree of life make up a large part of the total microbial diversity on the planet – and yet they lack some of the capabilities that are normally expected in any life form.”
The researchers found that the youngest common ancestors of these two lines could not breathe, just like their modern descendants. There was no oxygen in the atmosphere for the first two billion years of Earth’s existence. Today, oxygen is a key component of the Earth’s atmosphere and essential to the life it can support – but conditions have not changed just a few hundred feet underground, and this recent discovery suggests that some underground life has not either .
Scientists had previously speculated that because Patescibacteria and DPANN have very simple genetic traits and very simple metabolism, they must live symbiotically and rely on host organisms to survive. In the new study, the research team found no evidence that Patescibacteria and DPANN are dominated by symbionts – most of them appear to live as free cells and rely on the primitive fermentation pathway to supply themselves with energy.
“Dependence on other organisms is a characteristic of life,” said Jacob Beam, former postdoctoral fellow at Bigelow Laboratory and lead author of the study. “There are no absolute values in biology, and our research shows that microbes can vary along the spectrum of interdependencies.”
Scientists analyzed microbes from various environments around the globe, including a mud volcano at the bottom of the Mediterranean, hydrothermal springs in the Pacific and the world’s deepest gold mines in South Africa. Bigelow Laboratory’s bioinformatics scientist Julie Brown, research scientist Nicole Poulton, former postdocs Eric Becraft and Oliver Bezuidt, and student research experience intern Kayla Clark worked on this project along with an international team of scientists dedicated to field research, Computer analysis contributed to the laboratory and work.
These findings not only reveal the inner workings of the subsurface of the earth and the development of life, but can also provide a model system for what life on other planets could look like. Environments Mars and other bodies in the solar system are likely to resemble the subsurface of the earth, and Patescibacteria and DPANN are examples of life that seem to require very little energy to survive, which scientists expect as a prerequisite for life on other planets.
“This project would not have been possible without the collaboration of this diverse group of scientists who collect samples and pool their expertise around the world,” said Beam. “With a global group of scientists working together, we know more about the inner workings of these microbes that make up much of the total biodiversity on our planet.”
Reference: “Ancestral Absence of Electron Transport Chains in Patescibacteria and DPANN” by Jacob P. Beam, Eric D. Becraft, Julia M. Brown, Frederik Schulz, Jessica K. Jarett, Oliver Bezuidt, Nicole J. Poulton, Kayla Clark, Peter F. Dunfield , Nikolai V. Ravin, John R. Spear, Brian P. Hedlund, Konstantinos A. Kormas, Stefan M. Sievert, Mostafa S. Elshahed, Hazel A. Barton, Matthew B. Stott, Jonathan A. Eisen, Duane P. Moser , Tullis C. Onstott, Tanja Woyke and Ramunas Stepanauskas, August 17, 2020, Limits in Microbiology.
DOI: 10.3389 / fmicb.2020.01848
This work was funded by the National Science Foundation, the US Department of Energy, the Simons Foundation, the Russian Science Foundation, and the National Aeronautics and Space Administration.
