Two new microbes have been discovered that will force a rewrite of how we think the biological capacity to produce and consume methane evolved. The pair may have a role to play in the global methane cycle, but a member of the team who discovered them says the main significance of the discovery is for our understanding of early evolution.
“Methanogenic archaea are estimated to produce one billion tons of methane per year, with an equal amount estimated to be oxidized by archaeal methanotrophs,” the authors write in the paper announcing the discoveries, which is published in Science. However, all previous microorganisms with the capacity to metabolize methane are part of the Euryarchaeota phylum. The new discoveries are from the Bathyarchaeota, until recently known as the Miscellaneous Crenarchaeotal Group.
“The finding is like knowing about black and brown bears, and then coming across a giant panda,” said senior author Gene Tyson of the University of Queensland in a statement. “They have some basic characteristics in common, but in other ways these are fundamentally different.”
Speaking to IFLScience, Tyson added: “In some ways [methane processors] are even more diverse than bears, which are all mammals after all. These are different phylum so it changes our understanding of how methane metabolism evolved.”
Tyson explained that, like approximately 99% of microorganisms, we don’t know how to culture (grow) the new discoveries. “So we only know about them from their DNA sequences,” he said. These reveal that the new species, designated BA1 and BA2 until properly named, have genes that match those of known methane metabolisers, despite their enormously different place in the tree of life.
“The pathway can run in both directions, it can produce or consume methane depending on the species it is in,” Tyson said. Since we cannot culture either BA1 or BA2, we can’t see which one they do, but Tyson said that production seemed more likely, since both appear to lack an electron acceptor equivalent to the role oxygen performs for animals metabolising glucose.
Without this information it is impossible to know what role BA1 and BA2 play in the global methane cycle. Both were initially found in samples taken from a coal seam aquifer 600 meters (2,000 feet) beneath the Surat Basin in Queensland. However, Tyson told IFLScience: “Once we found them we screened lots of other locations, generally high methane environments at depths, such as Canadian tar sands.”
The genes detected are too similar to those in other methane-metabolizing species to be a case of convergent evolution, the authors believe, indicating conservation from an extraordinarily ancient common ancestor.
The Bathyarchaeota live in environments without oxygen, and usually also low in sulfur, often far beneath the sea. BA1 also carries genes for fermentation, while BA2 can break down fatty acids through β-oxidation. “Genes for fermentation are fairly common,” Tyson said. “What is unique is the ability to do fermentation and metabolize methane in the same organism.” Despite this party trick, Tyson does not expect either organism to prove industrially useful in the near future.
However, with methane detection considered one of the key possible signs of life on Mars, the findings may be of interest to astrobiologists.
3