New microbes are discovered in Yellowstone that can do something life should not be able to do

Life doesn’t always play by the tidy rules in textbooks. Most organisms use oxygen to produce ATP, which is energy used by cells. Some life forms, especially microbes, tap other chemicals when oxygen is scarce. The usual explanation says it’s one mode or the other.

A team studying a microbe from a Yellowstone hot spring found something different. This bacterium can use oxygen and sulfur at the same time to produce energy. That mixed strategy gives it an edge when oxygen levels fluctuate.

Lisa Keller of Montana State University is the lead author of this research that describes her work with bacterial samples from a group called Aquificales.

Along with her adviser and mentor Eric Boyd, professor in the College of Agriculture’s Department of Microbiology and Cell Biology, they published their fascinating work in the journal Nature Communications.

Microbes that breathe oxygen and sulfur

Respiration is how a cell converts food into usable energy (ATP). In oxygen-based respiration, cells move electrons through a chain of reactions and pass them to oxygen at the end.

Anaerobic respiration does a similar job but transfers electrons to other acceptors, such as sulfur, nitrate, or iron. Both strategies work; they are just different.

The hot-spring bacterium, Aquificales, challenged the usual either-or assumption. Under the right conditions, it kept both systems running.

That meant that while the bacteria were producing sulfide – an anaerobic process – they were using oxygen, meaning that both metabolisms were occurring.

“There’s no explanation other than that these cells are breathing oxygen at the same time that they are breathing elemental sulfur,” Keller said.

Keller explained that the bacterium’s ability to conduct both processes at once challenges our understanding of how microbes survive, especially in dynamic, low-oxygen environments such as hot springs. 

Oxygen and sulfur in hot springs

Hot springs are tough places to live. Temperatures run high. Minerals dissolve into the water. Gases bubble in and out.

Oxygen dissolves less in hot water than in cool water and escapes more easily, so levels change from moment to moment. In that kind of environment, a flexible energy strategy goes a long way.

The bacterium in this study thrives at high temperatures and feeds on simple molecules, including hydrogen gas. It can use oxygen when it’s available and elemental sulfur when oxygen dips.

How the study was done

Keller and her team isolated the microbe, then grew it in the lab at high temperatures with three ingredients: hydrogen gas as the energy source, elemental sulfur, and oxygen. They then tracked the cells’ chemical reactions and which genes were switched on.

Next, the team measured oxygen levels directly using gas chromatography. They also watched for the conversion of sulfur to sulfide, a clear sign of anaerobic sulfur respiration.

Gene expression data aligned with the chemistry: enzymes for both oxygen use and sulfur processing were active simultaneously.

Microbe’s oxygen-sulfur strategy

Cultures given hydrogen, sulfur, and oxygen grew faster and reached higher cell counts than cultures that had to use only oxygen or only sulfur.

That growth boost points to a simple payoff: more net energy when both pathways run together under low or unstable oxygen.

One detail matters for interpreting the results. The sulfide produced doesn’t persist in a mixed setup. Oxygen and certain metal ions in the broth can quickly consume it.

Without careful controls, that can hide the microbe’s dual strategy. This study accounted for that factor, which helps explain why this behavior may have been missed in past experiments.

Widespread pattern in nature

Genes and enzymes similar to those involved here are found in many microbes.

That suggests this hybrid mode could be more common than we realized, especially in places where conditions shift minute to minute. Hot springs and deep-sea vents contain fuels and oxidants that rise and fall.

Microbes that can keep multiple electron acceptors available may outgrow neighbors that wait for a single, ideal condition.

Flexibility like this also fits the story of early Earth. Oxygen didn’t flood the oceans all at once. It rose in patchy, inconsistent ways.

Microbes that could sense tiny amounts of oxygen while still relying on older, oxygen-free reactions likely had an advantage.

The results of this study may explain how ancient lifeforms adapted to the progressive oxygenation of Earth that began around 2.8 billion years ago – the Great Oxidation Event.

“This is really interesting, and it creates so many more questions,” Keller said. “We don’t know how widespread this is, but it opens the door for a lot of exploring.”

The Yellowstone bacterium isn’t ancient, but it shows a strategy that would have made sense when oxygen first began to matter.

How oxygen-sulfur combo works

Oxygen sits at the top of the energy ladder because it accepts electrons strongly, which usually means more energy per unit of fuel.

Sulfur compounds accept electrons too, though the energy yield is lower. When oxygen is scarce or fluctuating, using sulfur in parallel keeps the energy flowing rather than stalling.

Temperature and chemistry help set the stage. High heat speeds reactions and lowers oxygen solubility. Hydrogen gas, common around hydrothermal systems, supplies a steady stream of electrons.

Elemental sulfur is abundant in many volcanic and geothermal settings. Together, these conditions make simultaneous oxygen and sulfur respiration advantageous.

Real-world implications

Mixed respiration hints at new ways to run bioreactors and environmental cleanup efforts.

If microbes can be encouraged to keep more than one pathway active, engineers may squeeze extra efficiency from waste-to-energy systems, or keep pollutant breakdown steady when oxygen supply is uneven.

The same thinking applies to managing the sulfur and carbon cycles in complex settings where oxygen isn’t easy to control.

The work also urges careful experimental design. Testing a microbe in a strict “oxygen-only” or “no-oxygen” setup can miss behaviors that only appear when both are present.

Real environments rarely offer neat categories. Lab protocols that match those complex realities reveal strategies that would otherwise stay hidden.

To sum it all up, this heat-loving bacterium, Aquificales, broadens how we think about life’s energy playbook. It’s messy, adaptive, and full of clever workarounds that let microbes, and maybe eventually us, survive in a changing world.

The full study was published in the journal Nature Communications.

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