From Russia with methane

Microorganisms producing methane are not rare. In fact, the biological production of methane (CH4) is one of the key anaerobic processes in Earth’s biogeochemical carbon cycle. For humans, methane is a valuable source of (relatively clean) energy as well as a powerful greenhouse gas.

Three major pathways of methane production in microorganisms have been established. But the newly discovered methanonatronarcheia adds a whole new, fourth, pathway of methane production. It reduces methyl groups (-CH₃) into CH₄ with electrons it draws from hydrogen (H₂).

And it does so in conditions where other bacteria cannot survive: extreme alkaline (pH 10), extreme salinity (4 mol sodium per litre) and very hot (48-55 degrees Celsius).

Dr. Sorokin on location.

Dr. Dimitry Sorokin, who divides his time between Moscow (Winogradsky Institute of Microbiology) and Delft, has discovered the microbes in soda lakes in Siberia. He has been studying in these extreme surroundings since 2012.

According to Sorokin, “We when performed activity tests with substrates that typically activate methane production, we found some organisms that did not react. A year later, I manipulated the incubation conditions and I found what I was looking for. When I added sediment suspensions from the lakes, an explosive production of methane was the result.”

By filtering minuscule microbial lumps from the solution, Sorokin succeeded in isolating eleven pure cultures from various soda lakes within two years.

Surprise

When lab analyst Ben Abbas, one of the authors of the article, scanned the organism’s genome, the researchers were in for a surprise. The organism was not related to any of the other known methane-producing bacteria. In fact, it was a much earlier offshoot of life, before even bacteria came onto the stage. These so-called archea stem from the earliest days of life on earth and are currently mostly found near volcanic black smokers on the ocean floors.

According to Abbas, the great news is that such an old organism has found a niche in the Siberian soda lakes in which it can survive.

The organisms’ ability to convert organic materials into methane under extreme alkaline conditions and high temperatures may prove useful for biogas production since any CO2 that may arise as a by-product will remain in the solution.

• Dimitry Y. Sorokin, Kira S. Makariva, Ben Abbas et. al., Discovery of extremely halophilic, methyl-reducing euryarchaea provides insights into the evolutionary origin of methanogenesis, Nature microbiology, 25 May 2017, DOI: 10.1038/nmicrobiol.2017.81