Europe’s largest meteorite crater is home to deep ancient fungi

Broken rocks from impact craters have been proposed as suitable environments for deep colonization of microbial communities. In a new study published in Communication Earth and environment, a team of researchers shows that fungi have colonized deep parts of the largest impact crater in Europe, the Siljan impact structure, Sweden. Strikingly, it is as if the fungi fueled methane production in the crater.

At the picturesque Swedish lake of Siljan, an impressive impact structure of more than 50 km in diameter formed almost 400 million years ago. In newly discovered core points from drilling sites to deep in the crater, a team of researchers found fossil evidence of fungi.

The researchers examined an intensively fractured rock section at a depth level of 540 in the crater and observed fine filamentous structures in the vuggy rock. Upon closer inspection in the laboratory, it became clear to them that the filaments are petrified remnants of fungi. Fungi that resist the oxygen-free environment at these depths.

The relative abundance of different isotopes of carbon and sulfur in minerals found with respect to fungi, the researchers suggested that the fungi were involved in methane and sulfide formation processes in relationships with other inhabitants of the deep biosphere – bacteria and archeae.

Henrik Drake, from Linnaeus University, Sweden, and lead author of the study, explains the discovery: ‘The findings suggest that fungi may be widespread analysts of organic matter and overlook symbiotic partners to other, more primitive, microorganisms. seen, and thus can improve the production of greenhouse gases in the vast deep biosphere presented by rock. ‘

Radioisotopic dating of small calcite crystals formed after the formation of microbial methane revealed an age of the fungi fossils up to about 39 million years ago, more than 300 million years after the meteorite impact.

“We suggest that the anaerobic fungi decompose organic bituminous material in the fractures and produce hydrogen gas containing methanogens. This would be the first in situ finding ancient anaerobic fungi linked to methanogenesis at great depth in the continental crust, “says Magnus Ivarsson, at the Swedish Museum of Natural History and co-author of the study.

The impact structure, with a ring zone of degraded paleozoic sediments, was optimal for deep colonization of fungi, as energy sources in the form of organic and hydrocarbons migrate from overlying shales through the degraded crater.

“The conserved organic molecules that we were able to detect in the fungal remains give us additional evidence for a fungal origin and also for the proposed path of biological degradation of hydrocarbons derived by shale, which ultimately leads to methane production at depth,” he adds. Christine Heim, co-author, at, of the University of Cologne, Germany.

Henrik Drake says: “Microorganisms and their strategies for survival and colonization of the most hostile environments of the earth continue to amaze and surprise us, and here we add another mushroom piece to the puzzle of the deep biosphere.”

The results are presented in the article “Fossilized anaerobic and possibly methanogenesis-burning fungi identified deep within the Siljan impact structure, Sweden” in the Nature Journal Communication Earth and environment.