Bigelow Laboratory for Ocean Sciences

Curriculum Vitae

• Stepanauskas (PDF 148kb)

Education

• Ph.D., Limnology/Ecology, Lund University, Sweden, 2000
• M.A., Limnology, Lund University, Sweden, 1995
• B.A., Limnology, Uppsala University, Sweden, 1993

Research Interests

I am a microbial ecologist exploring the diversity and functioning of aquatic microbial communities. Bacteria and Archea are the most abundant and metabolically diverse forms of cellular life on Earth, greatly impacting global biogeochemical processes and human health and harboring an enormous potential for novel natural product discovery. However, the vast majority of environmental microorganisms do not grow in pure cultures and our knowledge about them is very limited.

I am a believer in the single-cell approach in microbial diversity, ecology, and evolution studies. Although this approach pushes the limits of current cell separation and sequencing technologies, it enables microbiological studies at the most biologically meaningful level - individual organism. Together with collaborators, I use a combination of fluorescence-activated cell sorting (FACS) and subsequent molecular analyses to determine metabolic capabilities of the uncultured microbial taxa in complex communities (see PNAS 104:9052–9057). This methodology can help answer fundamental microbial ecology questions as well as search for novel products for alternative energy production, pharmaceuticals, and other industrial applications. Currently we are developing procedures for single cell genomic sequencing and assembly of the yet uncultured microbial taxa, thus providing a powerful complement to metagenomic studies. In addition, we use single-cell DNA analyses to determine microbial trophic interactions, which form the food basis of aquatic ecosystems. Bigelow Laboratory hosted the first workshop on single cell genomics September 9-14, 2007.

My educational background is in the biogeochemistry of dissolved organic material, which constitutes one the largest global pools of carbon, nitrogen, phosphorus, and sulfur available for biological uptake. As part of a multi-disciplinary project, I collaborated with biologists, chemists, and geologists to understand the effects of the organic matter cycling on microbial community composition, ecosystem productivity, and drinking water quality in the Sacramento-San Joaquin River Delta and in the California State Water Project which delivers drinking water to over 20 million people. I also led a study of natural and anthropogenic inputs and eutrophication potential of organically bound nutrients to the Baltic Sea.

One of my current projects examines the indirect selection for antibiotic resistance by microbial exposure to toxic metals. The spread of antibiotic resistance among pathogenic bacteria is a major threat to public health. Clinical and agricultural uses of antibiotics have clearly increased the frequency of resistant pathogens. However, genes encoding antibiotic resistance are often located on mobile genetic elements, which carry multiple resistance factors. Therefore, it is plausible that exposure to chemically unrelated toxicants, especially heavy metals, may contribute to the maintenance and spread of antibiotic resistance. I am examining the frequency of metal and antibiotic resistant microorganisms, resistance-encoding genes, and horizontal gene transfer rates in pristine and metal-contaminated coastal areas, as well as in laboratory enclosures.

Select Publications

Stepanauskas R, Sieracki ME. 2007. Matching phylogeny and metabolism in the uncultured marine bacteria, one cell at a time. Proceedings of the National Academy of Sciences of the United States of America 104:9052–9057

Stepanauskas R, Glenn TC, Jagoe CH, Tuckfield RC, Lindell AH, King CJ, McArthur JV (2006) Co-selection for microbial resistance to metals and antibiotics in freshwater microcosms. Environmental Microbiology 8:1510-1514.

Baker BJ, Wright MS, Stepanauskas R, McArthur JV (2006) Co-selection of antibiotic and metal resistance. TRENDS In Microbiology 14:176-182

Stepanauskas R, Moran MA, Bergamaschi BA, Hollibaugh JT (2005) Sources, bioavailability, and photoreactivity of dissolved organic carbon in the Sacramento-San Joaquin River Delta. Biogeochemistry 74:131–149

Stepanauskas R, Moran MA, Bergamaschi BA, Hollibaugh JT (2003) Covariance of bacterioplankton composition and environmental variables in a temperate delta system. Aquatic Microbial Ecology 31:85-98

Stepanauskas R, Jorgensen NOG, Eigaard OR, Zvikas A, Tranvik LJ, Leonardson L (2002) Summer inputs of riverine nutrients to the Baltic Sea: Bioavailability and eutrophication relevance. Ecological Monographs 72:579-597

Stepanauskas R, Laudon H, Jorgensen NOG (2000) High DON bioavailability in boreal streams during a spring flood. Limnology and Oceanography 45:1298-1307

Stepanauskas R, Leonardson L, Tranvik LJ (1999) Bioavailability of wetland-derived DON to freshwater and marine bacterioplankton. Limnology and Oceanography 44:1477-1485

Stepanauskas R, Davidsson ET, Leonardson L (1996) Nitrogen transformations in wetland soil cores measured by N-15 isotope pairing and dilution at four infiltration rates. Applied and Environmental Microbiology 62:2345-2351

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