Fungi have colonized many parts of the world, including the impact craters of ancient meteors. New research reported in Communications Earth & Environment has shown that fungi were once growing deep within the the Siljan impact structure in Sweden, which is the largest impact crater in Europe. The fungi seem to have fueled methane production deep in the earth, possibly in partnership with other microorganisms.
It's thought that this impact crater formed around 400 million years ago, and scientists assessed samples from drills that went deep within the crater. Filamentous structures were observed in a section of very fractured rock. Close study suggested that these filaments were the fossilized remains of fungi, which are able to grow without oxygen at these depths. Other samples of ancient fungi fossils have recently been observed elsewhere.
The researchers assessed the samples to measure the abundance of various isotopes of carbon and sulfur in minerals that are related to fungi; the scientists suggested that this data may indicate that these fungi were involved in methane production. These fungi may have been working with microbes like bacteria and archaea and forming sulfides or methane in this process.
"The findings suggest that fungi may be widespread decomposers of organic matter and overlooked symbiotic partners to other, more primitive, microorganisms, thereby capable of enhancing the production of greenhouse gases in the vast rock-hosted deep biosphere," explained lead study author Henrik Drake of the Linnaeus University.
Radioisotopic dating of Calcite crystals that were probably formed by methane emitted from microbes revealed that the fungi fossils are about 39 million years old, from around 300 million years after the meteorite hit - so they are not extraterrestrial.
"We propose that the anaerobic fungi decomposed organic bituminous material in the fractures and produced hydrogen gas that fueled methanogens. This would be the first in situ finding of ancient anaerobic fungi linked to methanogenesis at great depth in the continental crust," said study co-author Magnus Ivarsson of the Swedish Museum of Natural History and co-author of the study.
Fungi have been able to grow in the impact crater because the fractures that were created opened up energy sources for these fungal organisms. The hydrocarbons in the sedimentary rock could be metabolized by fungi in a way that would explain the production of methane, noted the researchers.
"The preserved organic molecules that we could detect in the fungal remains give us additional evidence for a fungal origin and also for the proposed biodegradation pathway of shale-derived hydrocarbons, ultimately leading to production of methane at depth," added study co-author Professor Christine Heim, of University of Cologne, Germany.
"Microorganisms and their strategies for survival and colonization of Earth's most hostile environments continue to amaze and surprise us, and here we add another fungal piece to the deep biosphere jigsaw puzzle," said Drake.