A new study has affirmed the hypothesis that microorganisms which produce methane swim toward the hydrogen gas they need to stay alive.

In the process, the researchers discovered hydrogenotaxis, the movement of a biological cell toward hydrogen gas, and noticed that the cells were especially speedy when starving. They also made a video of the microorganism rushing toward its next meal.

The methane-producing organism,
Methanococcus maripaludis
, lives without oxygen, and it's classified as Archaea, one of the three domains of life. Since methanogenic Archaea live in anaerobic environments, ranging from salt marshes to wastewater treatment to the human microbiota. Whenever organic matter is being degraded, these microorganisms are typically present. 

(A) and (B) Field emission scanning electron micrographs of M. maripaludis pellicle with extracellular material and cells (indicated by arrows in (A)). Credit and link: doi:10.1038/srep03140

"They are the bottom of the food chain," said Matthew Fields, an associate professor in Montana State University's Department of Microbiology and co-author of the new paper. 

Hydrogenotaxis likely gives microorganisms a competitive advantage for accessing hydrogen in the environment. Fellow Montana State University microbiologist Gill Geesey, who was not involved with the work, said that hydrogenotaxis could represent an important strategy used by methanogens and other hydrogen-utilizing microbes for cycling of elements in natural and engineered processes. 

Methanococcus maripaludis is approximately one micron in diameter -- one millionth of a meter -- and can only be seen under the microscope. It is difficult to grow in a lab, one reason that researchers have been unable to verify earlier that Archaea organisms swim toward hydrogen gas, Fields said.

To conduct their research, the scientists created an oxygen-free environment in a fragile tube. Creating that environment was challenging, another reason that their discovery didn't occur earlier, Fields said.

After varying lengths of time, they released the cells into a solution to encounter hydrogen gas from the opposite end of the tube. That's where they proved what everyone had suspected – that Archaea swim through liquid toward hydrogen gas.

Every step in their experiments had to be done without breaking the tube or introducing oxygen, Fields said. It also had to be done inside an incubator with microscopes and computers. Computer software tracked the cells, proved they responded to hydrogen gas, and determined their speed.

Considering that speed relates to body length, Fields said the microbes moved faster than cheetahs, the fastest land animal on Earth.

Citation: Kristen A. Brileya, James M. Connolly, Carey Downey, Robin Gerlach& Matthew W. Fields, 'Taxis Toward Hydrogen Gas by Methanococcus maripaludis', Scientific Reports 3, Article number: 3140 doi:10.1038/srep03140