A metagenomic window into carbon metabolism at 3 km depth in Precambrian continental crust.
Subsurface microbial communities comprise a significant fraction of the global prokaryotic biomass; however, the carbon metabolisms that support the deep biosphere have been relatively unexplored. In order to determine the predominant carbon metabolisms within a 3-km deep fracture fluid system accessed via the Tau Tona gold mine (Witwatersrand Basin, South Africa), metagenomic and thermodynamic analyses were combined. Within our system of study, the energy-conserving reductive acetyl-CoA (Wood-Ljungdahl) pathway was found to be the most abundant carbon fixation pathway identified in the metagenome. Carbon monoxide dehydrogenase genes that have the potential to participate in (1) both autotrophic and heterotrophic metabolisms through the reversible oxidization of CO and subsequent transfer of electrons for sulfate reduction, (2) direct utilization of H2 and (3) methanogenesis were identified. The most abundant members of the metagenome belonged to Euryarchaeota (22%) and Firmicutes (57%)-by far, the highest relative abundance of Euryarchaeota yet reported from deep fracture fluids in South Africa and one of only five Firmicutes-dominated deep fracture fluids identified in the region. Importantly, by combining the metagenomics data and thermodynamic modeling of this study with previously published isotopic and community composition data from the South African subsurface, we are able to demonstrate that Firmicutes-dominated communities are associated with a particular hydrogeologic environment, specifically the older, more saline and more reducing waters.
Department of Geosciences, Guyot Hall, Princeton University, Princeton, NJ, USA.
Cara
C
Magnabosco
Department of Geosciences, Guyot Hall, Princeton University, Princeton, NJ, USA.
Kathleen
K
Ryan
Department of Geosciences, Guyot Hall, Princeton University, Princeton, NJ, USA.
Maggie C Y
MC
Lau
Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, Bloemfontein, South Africa.
Olukayode
O
Kuloyo
Department of Earth Sciences, University of Toronto, Toronto, Ontario, Canada.
Barbara
B
Sherwood Lollar
Department of Biology, New Mexico Institute of Mining and Technology, Socorro, NM, USA.
Thomas L
TL
Kieft
Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, Bloemfontein, South Africa.
Esta
E
van Heerden
Department of Geosciences, Guyot Hall, Princeton University, Princeton, NJ, USA.
Tullis C
TC
Onstott
D052818:Autotrophic Processes; D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D002244:Carbon / Q000032:analysis / Q000378:metabolism*; D057486:Carbon Cycle; D005618:Fresh Water / Q000382:microbiology*; D019015:Geologic Sediments / Q000382:microbiology*; D052836:Heterotrophic Processes; D054892:Metagenome; D056186:Metagenomics; D008906:Mining; D010802:Phylogeny; D013019:South Africa
D002244:Carbon