Tanja Bosak, Ph.D.

Associate Professor of Geobiology, Massachusetts Institute of TechnologyTanja Bosak, Ph.D.’s Website

Project: Record of Microbial and Geochemical Co-evolution in Cyanobacterial Genomes

Cyanobacteria have the longest and most continuous fossil record of all organisms. This fossil record is used to time events in the evolution of different cyanobacterial groups, as encoded by the genomes of modern cyanobacteria, and reveal links between ecological, evolutionary and geochemical changes on Earth’s surface. However, current time-calibrated models of cyanobacterial evolution (molecular clocks) rely on a simple fossil morphology whose cyanobacterial origin and taxonomic associations have been questioned. Furthermore, most taxonomically diagnostic cyanobacterial fossils represent benthic organisms, but the sampling of modern cyanobacterial genomes is biased toward unicellular planktonic taxa.

The work proposed here will improve the sampling of the cyanobacterial phylum and the understanding of its evolution through three major aims:

  1. To sequence and annotate the genomes of 40-60 undersampled, but geologically and environmentally relevant cyanobacterial taxa;
  2. To reconstruct major genomic events (gene additions, duplications and losses) in cyanobacterial history;
  3. To correlate these data with major events in Earth history and correlate events in cyanobacterial evolution with the evolution of other organismal groups which may lack a fossil record.

Sequencing efforts will use pure cultures from existing collections, or sorted cells/filaments from enrichment cultures and field samples. Modern homologs of the most taxonomically diagnostic and oldest unambiguous cyanobacterial fossils are not well represented in culture collections, so these samples will be obtained in the field. The newly sequenced genomes will be used to re-estimate divergence times using a relaxed molecular clock and new calibration points will be provided. Based on this analysis, genome reconciliation will be performed. The new cyanobacterial molecular clock will be used to correlate major gene acquisitions, losses and duplications with known events in Earth history or to hypothesize currently unknown events based on genomic data.


Tanja Bosak was born in Croatia and graduated from the Zagreb University with a degree in Geophysics. After a summer of research at JPL and a short stint as a meteorologist at the Zagreb Airport, she moved to the California Institute of Technology in Pasadena, where she studied signatures of microbial processes in ancient sedimentary rocks and earned a Ph.D. in Geobiology. She spent two years at Harvard as a Microbial Initiative Postdoctoral Fellow, joined the Department of Earth, Atmospheric and Planetary Sciences at MIT in 2007 and is now an associate professor of Geobiology. Tanja’s work integrates microbiology, sedimentology and stable isotope geochemistry into experimental geobiology to ask how microbes shape sedimentary rocks, how organisms fossilize and how microbial metabolisms leave biogeochemical patterns in sediments. Her lab uses this approach to explore modern biogeochemical and sedimentological processes and interpret the record of life on the Early Earth. For this work, and her work with graduate students and undergraduates, Bosak received the Subaru Outstanding Woman in Science award by the Geological Society of America (2007), the Macelwane Medal from the American Geophysical Union (2011), the Edgerton Award for young faculty at MIT (2012) and the Undergraduate Research Opportunities for Undergraduates Mentor of the Year award by MIT (2012). Bosak is a fellow of the American Geophysical Union (2011) and one of the subject editors of Geobiology.


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