Orsi, William D.; Edgcomb, Virginia P.; Christman, Glenn D.; Biddle, Jennifer F.
Scientific ocean drilling has revealed a deep biosphere of widespread microbial life in sub-seafloor sediment. Microbial metabolism in the marine subsurface likely plays an
important role in global biogeochemical cycles1-3 but deep biosphere activities are not well
understood1. Here, we describe and analyze the first subseafloor metatranscriptomes from
anaerobic Peru Margin sediment up to 159 meters below seafloor (mbsf) represented by
over 1 billion cDNA sequence reads. Anaerobic metabolism of amino acids, carbohydrates,
and lipids appear to be dominant metabolic processes, and profiles of dissimilatory sulfite
reductase (Dsr) transcripts are consistent with porewater sulfate concentration profiles1.
Moreover, transcripts involved in cell division increase as a function of microbial cell
concentration, indicating that increases in subseafloor microbial abundance are a function of cell division across all three domains of life. These data support calculations1 and
models4 of subseafloor microbial metabolism and represent the first holistic picture of deep