In
addition to the life on the surface of Earth and in its oceans, ecosystems have
evolved deep under us in a realm coined the "deep biosphere" which
stretches several kilometers down into the bedrock. Down there, the conditions
are harsh and life is forced to adjust to a lifestyle that we at the surface
would call extreme. One major difference to surface conditions is the lack of
oxygen; a compound we take for granted and consider to be a prerequisite for
survival but which subsurface life has to cope without.
The
knowledge about ancient life in this deep environment is extremely scarce and
most studies so far have focused on the prokaryotes. A new study by an
international team of researchers led by Dr Henrik Drake of the Linnaeus
University and Dr Magnus Ivarsson of the Swedish Museum of Natural History sheds
light on eukaryotes in this deep setting. They present the first in situ
finding of fungi at great depth in the bedrock. This ancient life is found at
740 m below the ground surface. It represents a new piece in the deep biosphere
puzzle.
High
spatial resolution isotope analysis within the minerals that occur along with
the fungi revealed that a variety of microbial processes had occurred in the
caveat, including methane consumption and sulfate reduction. The fungi could
not be dated precisely but there are proxies pointing to an age of tens of
millions of years.
The
study confirms a previously hypothesized consortium between fungi and sulfate
reducing bacteria, a coupling that has yet been unsupported by direct evidence
in nature. As fungi provide hydrogen gas that fuel prokaryotes, the findings
suggest a re-evaluation of the energy cycling within the energy-poor deep
continental biosphere. Eukaryotes have been neglected in the deep biosphere
research. This new finding proposes that they may be key players in this
globally vast realm.
Studies
of subterranean life-forms have implications for early life on our planet and
for life on other planets, where hostile conditions may have inhibited
colonization of the surface.
See:
Henrik Drake, Magnus Ivarsson, Stefan
Bengtson, Christine Heim, Sandra Siljeström, Martin J. Whitehouse, Curt Broman,
Veneta Belivanova, Mats E. Åström. Anaerobic consortia of fungi
and sulfate reducing bacteria in deep granite fractures. Nature
Communications, 2017; 8 (1) DOI: 10.1038/s41467-017-00094-6
Posted by Dr. Tim Sandle