Research shows that two large microbial groups are unable to breathe

A new scientific study has revealed unique life strategies of two large groups of microbes that live beneath the earth’s surface. A publication in Frontiers in microbiology reports that these groups, originally thought to rely on symbiotic relationships with other organisms, can also live independently and use an ancient mode of energy production.

“These microbes, belonging to the groups Patescibacteria and DPANN, are really special, really exciting examples of the early evolution of life,” said Ramunas Stepanauskas, a senior research scientist at Bigelow Laboratory for Ocean Sciences and an author of the paper. “They may be remnants of ancient life forms that have been hidden and flourishing in the earth’s subsoil 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 showed that these two groups of abundant microbes have the ability to breathe to synthesize ATP, the common energy currency of life.

The team found that these microbes, which live in a variety of environments within the Earth’s interior, only seem to obtain energy through the process of fermentation. Many organisms are fermenting, including humans as their muscles absorb oxygen during intense exercise – but they only use it as an additional source of energy.

“Our findings indicate that Patescibacteria and DPANN are ancient life forms that may have never learned how to breathe,” Stepanauskas said. “These two important branches of the evolutionary tree of life form a large part of the total microbial diversity on the planet – and yet they lack some possibilities that are typically expected in any life form.”

The researchers found that the most recent common ancestors of these two lines lacked the ability to breathe, just as their modern descendants do. For the first two billion years of the earth’s existence, there was no oxygen in the atmosphere. Today, oxygen is an important part of the Earth’s atmosphere and essential to life that it can support – but only a few hundred feet underground the circumstances have not changed, and this recent discovery suggests that some underground life does not either.

Scientists had previously speculated that because Patescibacteria and DPANN have very simple genetic functions and metabolism, they must live symbiotically and depend on host organisms to survive. In the new study, the research team found no evidence that Patescibacteria and DPANN are dominated by symbionts – most appear to live as free cells and rely on the primitive path of fermentation to supply themselves with energy.

“Dependence on other organisms is a hallmark of life,” said Jacob Beam, a former postdoctoral researcher at Bigelow Laboratory and lead author of this study. “There are no absolutes in biology, and our research shows that microbes can differ across the spectrum of interdependence.”

Scientists analyzed microbes from various environments around the world, including a mud volcano at the bottom of the Mediterranean Sea, hydrothermal vents in the Pacific Ocean, and the world’s deepest gold mines in South Africa. Bigelow Laboratory Bioinformatics Scientist Julie Brown, Research Scientist Nicole Poulton, Former Postdoctoral Research Scientists Eric Becraft and Oliver Bezuidt, and Research Experience for Undergraduate Students Kayla Clark worked on this project, along with an international team of scientists who contributed to fieldwork, laboratory , and calculation analyzes.

In addition to revealing the inner workings of the Earth’s subsoil and the evolution of life, these findings may provide a model system for what life on other planets might look like. Environments on Mars and other bodies in the solar system are likely to resemble the Earth’s subsoil, and Patescibacteria and DPANN represent examples of life that appear to require little energy to survive, which scientists expect a requirement for life on other planets would be.

“This project would not have been possible without the collaboration of this diverse group of scientists who collect samples from around the world and unite their expertise,” said Beam. “Through the collaboration of a global group of scientists working together, we know more about the intrinsic workings of these microbes that form a significant fraction of the total biodiversity on our planet.”