Iron-rich Microbial Mats’ Main Players: Marsarchaeota

Novel archaeal lineage found in Yellowstone may have been important in early Earth conditions.

The Science

The iron (Fe)-oxide terraces at Echinus Geyser form from the oxidation of ferrous Fe, and the temperature across the terraces ranges from ~ 60-70ºC, while pH values vary from 3.4 to 3.6. A very thin (1-2 mm) layer of water flowing over the Fe-oxide terraces from the outflow channel at Echinus Geyser, located in Yellowstone National Park’s Norris Geyser Basin, is thought to provide the needed oxygen to create habitats suitable for the Marsarchaeota. (Bill Inskeep)

Through a combination of sequencing tools and techniques applied to samples collected from acidic iron-oxide microbial mats in Yellowstone National Park over time, researchers have discovered and characterized a novel phylum-level lineage of archaea with at least two major subgroups dubbed Marsarchaeota.

The Impact

Iron cycling is thought to have played a key role in the development of life on Earth; the iron-oxide microbial mats at Yellowstone offer researchers an analog for studying early Earth conditions. Additionally, high-temperature (thermophilic) microbes are of interest for their potential use in number of biotechnological applications. Molecular biology has benefited from heat-stable enzymes derived from thermophiles, stabilizing the polymerase chain reaction technology that enables researchers to generating thousands to millions of copies of a particular DNA sequence from just a few pieces of DNA.

Summary

The extreme environments found in Yellowstone National Park include a wide range of temperatures, levels of acidity and geographical features, and the archaeal lineages found there and elsewhere provide researchers with insights into the evolution of life on Earth. For decades, longtime JGI collaborator Bill Inskeep of Montana State University has been conducting microbial field studies at Yellowstone, and in this latest report, published in Nature Microbiology, he and his team describe a candidate phylum-level lineage of aerobic archaea found in iron-oxide microbial mats. The reddish hues caused by the presence of iron led Inskeep and his colleagues to name the archaeal lineage for the planet Mars.

To help determine where Marsarchaeota might fall amidst other known archaeal lineages, the team relied on a combination of phylogenomic analyses, transcriptomics for microbial genomic activity (gene expression), and direct microscopy. Through the JGI’s Community Science Program, the team used metagenome assemblies, transcriptomes and single amplified genomes from samples collected from several locations to thoroughly characterize the archaeal lineage, information that they believe will lend insights into discussions on the origin of archaea. They report that the Marsarchaeota are a sister group to the archaeal lineage named Geoarchaeota that Inskeep’s team had previously identified and characterized, also with JGI’s help. Additionally, the Marsarchaeota comprise 20-50 percent of the iron-oxide microbial mat communities in the 60-80°C temperature range.

The discovery of aerobic, thermophilic Marsarchaeota in these microbial mats provides the team with clues on how early life evolved on Earth as iron is believed to have played a key role in redox processes important in the formation and evolution of early life on Earth. One of the questions is how Marsarchaeota can access oxygen in low-oxygen habitats such as these microbial mats. Inskeep suggested that the thin film of water that runs over the iron-oxide microbial mats at the geyser sites is providing just enough oxygen to the Marsarchaeota. “Proving that is an entirely different process,” he added.

The Marsarchaeota furnish greater definition of the roots of the tree of life on Earth, and their broad distribution suggests that iron-oxidizing habitats, similar to those in Yellowstone from which the Marsarchaeota were isolated and identified, may have been important to the early evolution of these microbes.

BER Contact

Daniel Drell, Ph.D.
Program Manager
Biological Systems Sciences Division
Office of Biological and Environmental Research
Office of Science
US Department of Energy
daniel.drell@science.doe.gov

PI Contact

Bill Inskeep
Montana State University
binskeep@montana.edu

Funding

The work conducted by the U.S. Department of Energy Joint Genome Institute is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The work was supported by Pacific Northwest National Laboratory, National Science Foundation Integrative Graduate Education and Research Traineeship Program, and Montana Agricultural Experiment Station (W.P.I.). Computations were performed on the Hyalite High-Performance Computing System, operated and supported by MSU’s Information Technology Center.

Publication

Jay ZJ et al. Marsarchaeota are an aerobic archaeal lineage abundant in geothermal iron oxide microbial mats. Nat Microbiol. 2018 May 14. doi: 10.1038/s41564-018-0163-1. [Epub ahead of print]