Dr. Christopher Sedlacek

Research Interests and Background           

Currently, I’m focused on investigating the ecophysiological and genomic characteristics of microorganisms involved in nitrification (nitrifiers): ammonia-oxidizing bacteria and archaea, nitrite-oxidizing bacteria, and the recently discovered comammox bacteria.

            Nitrifiers play an important role in both natural and engineered environments, transforming ammonia (NH₃) via nitrite (NO₂^-) to nitrate (NO₃^-). For example, nitrification is essential for proper wastewater and drinking water treatment. However, nitrification also contributes to fertilizer loss from agricultural systems through nitrogen leaching, run-off, and greenhouse gas emissions. This loss leads to the excessive application of nitrogen-based fertilizers and the eutrophication of downstream aquatic ecosystems. This puts understanding nitrifiers at the heart of some large ecological questions:

• Can we increase the efficiency of nitrification during water treatment? (Faster, more robust nitrification)
• Can we create nitrifying communities that emit less greenhouse gases? (More environmentally friendly nitrification)
• Can we inhibit nitrification in agricultural soils, where it steals nitrogen from crops? (Slower or inhibited nitrification)

            My goal is to apply my understanding of nitrifier genomics and physiological traits to better inform nitrogen management practices in both engineered and natural ecosystems. In order to do this, I use a variety of culture dependent and independent approaches:

• Cultivation of nitrifiers

            Continuous bioreactors, novel environmental enrichment cultures, and mock community cultures

• Physiological experiments

            Microrespiration, growth rate, and substrate utilization experiments

• Comparative genomics

            Identifying core genomes, essential nitrification genes, and curating currently unknown genes

       These techniques enable me to investigate and characterize nitrifiers from their initial detection in environmental samples to their growth characteristics once isolated and at each stage in between. I’m currently focused on the isolation of several novel nitrifiers, the characterization of substrate kinetics, and the genomic and physiological investigation of alternative metabolisms in nitrifiers.

            In addition to nitrification specific topics, I also have general research interests including the cultivation of currently unculturable or fastidious microbes, microbial community interactions, and microbial adaptations to extreme environments.

Current Projects

I'm currently involved in several on going projects within the framework of the PLAYNICE project.

Select publications from ongoing projects

Kits KD, Sedlacek CJ, Lebedeva EV, Han P, Bulaev A, Pjevac P, Daebeler A, Romano S, Albertsen M, Stein LY, Daims H, Wagner M. 2017. Kinetic analysis of a complete nitrifier reveals an oligotrophic lifestyle. Nature, 549: 269-272.

Sedlacek CJ, Nielsen S, Greis KD, Haffey WD, Revsbech NP, Ticak T, Laanbroek HJ, Bollmann A. 2016. Effects of bacterial community members on the proteome of the AOB Nitrosomonas sp. strain Is79. Applied and Environmental Microbiology, 7(3):469

Sedlacek CJ, McGowan B, Suwa Y, Sayavedra-Soto L, Laanbroek HJ, Stein LY, Norton JM, Klotz MG, Bollmann A. 2019. A Physiological and Genomic Comparison of Nitrosomonas Cluster 6a and 7 Ammonia-Oxidizing Bacteria. Microbial Ecology, 78: 985-994.

Daebeler A, Herbold CW, Vierheilig J, Sedlacek CJ, Pjevac P, Albertsen M, Kirkegaard RH, De La Torre JR, Daims H, Wagner M. 2018. Cultivation and Genomic Analysis of “Candidatus Nitrosocaldus islandicus,” an Obligately Thermophilic, Ammonia-Oxidizing Thaumarchaeon from a Hot Spring Biofilm in Graendalur Valley, Iceland. Front. Microbiol. 9:193.