High CO2 subsurface environment enriches for novel microbial lineages capable of autotrophic carbon fixation

Tuesday, 15 December 2015: 13:55
2008 (Moscone West)
Alexander Josef Probst1, Jessica Jerett2, Cindy J Castelle1, Brian C Thomas1, Itai Sharon1, Christopher T Brown1, Karthik Anantharaman1, Joanne B Emerson3, Alex Whitmore Hernsdorf1, Yuki Amano4, Yohey Suzuki5, Susannah G Tringe2, Tanja Woyke2 and Jillian F Banfield1, (1)University of California Berkeley, Berkeley, CA, United States, (2)Joint Genome Institute, Walnut Creek, CA, United States, (3)Ohio State University Main Campus, Columbus, OH, United States, (4)JAEA Japan Atomic Energy Agency, Toki, Japan, (5)University of Tokyo, 4Department of Earth and Planetary Science, Tokyo, Japan
Subsurface environments span the planet but remain little understood from the perspective of the capacity of the resident organisms to fix CO2. Here we investigated the autotrophic capacity of microbial communities in range of a high-CO2 subsurface environments via analysis of 250 near-complete microbial genomes (151 of them from distinct species) that represent the most abundant organisms over a subsurface depth transect. More than one third of the genomes belonged to the so-called candidate phyla radiation (CPR), which have limited metabolic capabilities. Approximately 30% of the community members are autotrophs that comprise 70% of the microbiome with metabolism likely supported by sulfur and nitrogen respiration. Of the carbon fixation pathways, the Calvin Benson Basham Cycle was most common, but the Wood-Ljungdhal pathway was present in the greatest phylogenetic diversity of organisms. Unexpectedly, one organism from a novel phylum sibling to the CPR is predicted to fix carbon by the reverse TCA cycle. The genome of the most abundant organism, an archaeon designated “Candidatus Altiarchaeum hamiconexum”, was also found in subsurface samples from other continents including Europe and Asia. The archaeon was proven to be a carbon fixer using a novel reductive acetyl-CoA pathway. These results provide evidence that carbon dioxide is the major carbon source in these environments and suggest that autotrophy in the subsurface represents a substantial carbon dioxide sink affecting the global carbon cycle.