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Prof. Dr. William Orsi

Overarching research theme

Our research focuses on the biological and biochemical mechanisms underlying marine microbial loops: the biogeochemical cycling of carbon and its processing through microbial food webs in the ocean. We use a combination of stable isotope probing, genomic, and gene expression tools. Our research is derived primarily from field observations, as well as DNA and RNA stable isotope labeling experiments.

1) Pelagic microbial loop

We seek to better understand how the metabolic diversity of microbial life is linked to the efficiency of the “biological pump”, the ocean’s biologically driven sequestration of carbon from the atmosphere to the deep sea. A major goal is to better understand how these processes are linked both in the modern ocean and over the last glacial-interglacial cycle in sedimentary records of ancient DNA and paleoclimate.

Selected publications

Orsi W, Smith JM, Liu S, Liu Z, Sakamoto CM, Wilken S, Poirier C, Richards TA, Keeling PJ, Worden AZ, Santoro AE (2016) Diverse, uncultivated bacteria and archaea underlying the cycling of dissolved protein in the ocean. The ISME Journal 10, 2158-2173.

Orsi W, Smith JM, Wilcox HM, Swalwell JE, Carini P, Worden AZ, Santoro AE (2015). Ecophysiology of uncultivated marine euryarchaea is linked to particulate organic matter. The ISME Journal 9: 1747-1763.

Santoro AE, Dupont CL, Richter RA, Craig MT, Carini P, McIlvin MR, Yang Y, Orsi W, Moran D, Saito MA (2015). Genomic and proteomic characterization of ‘Candidatus Nitrosopelagicus brevis’: an ammonia-oxidizing archaeon from the open ocean. PNAS 114:1173-1178.

Coolen MJL, Orsi W, Balkema C, Quince C, Harris K, Sylva S, Filipova-Marinova M, Giosan L. (2013). Evolution of the plankton paleome in the Black Sea from the Deglacial to Anthropocene. PNAS 110(21): 8609-14.

Orsi W, Song Y, Hallam S, Edgcomb V. (2012). Effect of oxygen minimum zone formation on communities of marine protists. The ISME Journal 6: 1586-1601.

Orsi W, Edgcomb V, Jeon S O, Leslin C, Bunge J, Taylor G T, Varela R, Epstein S. (2011). Protistan microbial observatory in the Cariaco Basin, Caribbean. Part II. Habitat specialization. The ISME Journal 5:1344-1356.

2) Subsurface microbial carbon cycling

Organic matter escaping remineralization by the pelagic microbial loop is deposited at the seafloor and slowly buried in the subsurface. A major goal is to link the cycling of detrital compounds with the diverse microbial metabolisms that change in response to energy availability and redox gradients in marine sediments. We are also interested in “dark microbial loops” at deep sea low temperature hydrothermal vents, where chemolithoautotrophic microbes are able to fix CO2 in the absence of sunlight, fueled by geological energy sources. We seek to better understand the evolution of this process throughout the geological record, its role in the origins of life, and the mechanisms by which it supports life and ecosystems.

Selected publications

Orsi W* (2018) Ecology and evolution of seafloor and subseafloor microbial communities. Nature Reviews Microbiology 16, 671-683.


Orsi W*, Richards TA, Francis WR (2018) Predicted microbial secretomes and their target substrates in marine sediments. Nature Microbiology 3: 32-37.

Klein F, Humphris SE, Guo W, Schubotz F, Schwarzenbach EM, Orsi WD (2015) Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin. PNAS 112, 12036-12041.

Orsi W, Edgcomb V, Christman G, Biddle J. (2013). Gene expression in the deep biosphere. Nature 499: 205-208.

Orsi W, Biddle J, Edgcomb, V. (2013). Deep sequencing of subseafloor eukaryotic rRNA reveals active Fungi across multiple subseafloor provinces. PLoS ONE 8(2): e56335.