NOVEL ARCHAEAL LINEAGES UTILIZING RUBISCO IN LAKE SUPERIOR SEDIMENTS

The archaeal tree of life has recently been rapidly expanding, driven primarily due to advancements in metagenomic techniques. To date, much work has been done that explores Archaeal diversity in marine settings, while there is a lack of exploration of freshwater lake sediments. Using sediments from Lake Superior, a large, cold, oligotrophic lake with low sediment carbon and high nitrate, we describe the diversity, metabolic capabilities and transcript activity of Archaea across spatial and depth gradients. Approximately 170 metagenome assembled genomes (MAGs) were recovered that belong to four main clades, Thaumarchaeota, Basal Thaumarchaeota, Thermoplasmata, and Woesarchaeota, along with a member of a deeply branching DPANN Phylum. Ribulose bisphosphate carboxylase/oxygenase (RuBisCO) sequences were detected in the deeply branching DPANN genome, Woesarchaeota, and one Basal Thaumarchaeota. We present evidence that these archaea likely utilize RuBisCO in a regenerative pathway that fixes CO₂ and can scavenge nucleosides, nucleotides, and sugars.