Networked Speaker Series #15

May 11, 2017

Dr. Drew Steen, University of Tennessee Knoxville

What Heterotrophs Want: Using extracellular enzyme assays to probe the lifestyle of heterotrophic microorganisms in subsurface sediments


A large fraction of cells in subsurface sediments are heterotrophs, and many of those are only distantly related to taxa that have been grown in culture. Because the enzymes involved in organic carbon metabolism are structurally diverse, it is difficult to determine the precise environmental function of heterotrophic microorganisms from genomic/transcriptomic data alone. In this talk, I will describe my and my collaborators’ recent efforts to use the activities of extracellular enzymes to better understand how heterotrophic microorganisms in subsurface sediments access their food. In sediments of the White Oak River estuary in North Carolina, activities of extracellular peptidases (protein-degrading enzymes) suggest that subsurface heterotrophic microorganisms are adapted to consume old, recalcitrant organic matter. Assays from deep sediments of the Baltic Sea Basin collected during IODP Expedition 347 show that cells in sediments up to 50 m deep use extracellular enzymes to access complex organic matter, but that the scope for adaptation to subsurface conditions is limited. These results yield insight into the mechanisms by which subsurface heterotrophic microorganisms stay alive, and put some constraints on the range of conditions in which heterotrophy based on detrital organic matter is a viable metabolic strategy. 

Speaker Biography

Drew Steen is assistant professor of Earth and Planetary Sciences at the University of Tennessee, Knoxville. He studies interactions between microorganisms and complex organic matter in environments ranging from small mountain streams to the marine subsurface. He gets excited about environmental organic chemistry, microbial ecology, and reproducible data analysis. Check his website at, or his twitter feed at @drdrewsteen.