A group of Montana State University microbiologists has discovered a new archaeal lineage living in the extreme geothermal environments in Yellowstone National Park. The discovery, reported in the journal Nature Microbiology, sheds new light on the evolution of the Archaea and the importance of iron in early life.
Three major populations from Echinus Geyser, Yellowstone National Park: Marsarchaeota (>1 µm cocci, red arrow), Thermocladium spp. (0.3–0.4 µm diameter filaments), and Sulfolobus islandicus-like organisms (<0.8 µm cocci). Scale bar – 1 µm. Image credit: Jay et al, doi: 10.1038/s41564-018-0163-1.
The Archaea are one of the primary domains of cellular life, the others being bacteria and eukaryotes.
Like bacteria, these microorganisms are prokaryotes, meaning that they have no cell nucleus or any other organelles in their cells.
They are possibly the most ancient form of life: putative fossils of archaeal cells in stromatolites have been dated to almost 3.5 billion years ago. They thrive in a bewildering variety of habitats, from the familiar — soils and oceans — to the inhospitable and bizarre.
“The discovery of archaeal lineages is critical to our understanding of the universal tree of life and evolutionary history of the Earth,” said Montana State University’s Professor William Inskeep and co-authors.
“Geochemically diverse thermal environments in Yellowstone National Park provide unprecedented opportunities for studying Archaea in habitats that may represent analogues of early Earth.”
Professor Inskeep and colleagues named the new archaeal lineage the Marsarchaeota after Mars, because these organisms thrive in habitats containing iron oxides.
Within the Marsarchaeota, they discovered two main subgroups that live throughout Yellowstone National Park and thrive in hot, acidic water where iron oxide is the main mineral.
One subgroup lives in water above 122 degrees Fahrenheit (50 degrees Celsius), and the other lives in water above 140 to 176 degrees Fahrenheit (60-80 degrees Celsius). The water is about as acidic as grapefruit juice. Their microbial mats are red because of the iron oxide.
“It’s interesting that the habitat of these organisms contains (iron) minerals similar to those found on the surface of Mars,” Professor Inskeep said.
“Microbes produce iron oxide, but the Marsarchaeota do not. They might be involved in reducing iron into a simpler form, which is important from an early Earth standpoint. Iron cycling has been implicated as being extremely important in early Earth conditions.”
“The Marsarchaeota live fairly deep in microbial mats, but they still require low levels of oxygen,” he added.
“The subgroups are so abundant that, together, they can account for as much as half of the organisms living within a single microbial mat.”
Zackary J. Jay et al. Marsarchaeota are an aerobic archaeal lineage abundant in geothermal iron oxide microbial mats. Nature Microbiology, published online May 14, 2018; doi: 10.1038/s41564-018-0163-1