Studies of Earth’s deep biosphere tend to focus on microbial life, primarily prokaryotic single-celled organisms. However, in 2011, DCO researchers Gaetan Borgonie (Extreme Life Isyensya in Gentbrugge, Belgium) and colleagues showed that nematode worms could survive several kilometers underground. Now the team reports other multicellular animals are also thriving at depth. Their most recent work is published in Nature Communications .
To access the deep crustal biosphere, Borgonie travelled to the deep mines of South Africa. There, in some of the deepest mines on Earth, he and his colleagues sampled fissure fluids, which had been trapped underground for up to 12,300 years. The samples they collected are the result of an extensive two-year campaign, with much of the analysis conducted in Esta van Heerden’s lab at the University of the Free State in Bloemfontein, South Africa.
The authors show that several eukaryotic species, in addition to the nematode worms previously described , are living in these deep fissures. Borgonie et al. show evidence for Platyhelminthes, Rotifera, Annelida, and Arthropoda, as well as an additional species of Nemotoda, thriving up to 1.4 km deep.
“It is very crowded in some places down under,” said Gaetan Borgonie. “It’s a veritable zoo!”
By comparing the genomes of these deep-dwelling species with their surface relatives, the authors also provide hypotheses for how the animals survive in low oxygen, high pressure, and high temperature environments. For several species, their closest ancestors were already adapted to living in a variety of habitats, thus they possess an inherent genetic plasticity. Others are smaller than their surface counterparts, and can better withstand high pressures. Additional adaptation mechanisms include changes in reproductive behavior and an increased propensity to form biofilms.
With such a surprisingly diverse deep biosphere here on Earth, this research not only transforms our understanding of our own planet, but also how we think about potential subterranean habitats on other planetary bodies.
Click the image to the left for a video of nematodes courtesy of the BBC, which originally appeared in this news article on 24 November 2015.
Image: A scanning electron microscopy image shows a nematode moving amid a filmy structure called biofilm. The scale bar at the left is 20 micrometers long. (Courtesy of Gaetan Borgonie, Extreme Life Isyensya, Belgium)