Date of Graduation
Master of Science in Cell & Molecular Biology (MS)
Second Committee Member
Carbon, Diatoms, Evolution, Nitzschia, Nonphotosynthetic
Diatoms are prolific photosynthesizers responsible for some 20% of global primary production.
In real terms, the oxygen in one of every five breaths traces back to photosynthesis by marine
diatoms. Among the tens of thousands of diatom species, a small handful of colorless diatom
species in the genus Nitzschia have lost photosynthesis altogether and rely exclusively on
extracellular organic carbon for growth. I used DNA sequence data to reconstruct the phylogeny
of this group, and found that nonphotosynthetic diatoms are monophyletic, indicating that
photosynthesis was lost just one time over the course of some 200 million years of diatom
evolution. Carbon metabolism in nonphotosynthetic diatoms, including the exact source of
carbon used by these species, has not been fully characterized. We sequenced the nuclear genome
of one species and used it to develop a comprehensive model of central carbon metabolism.
Preliminary analysis of Nitzschia metabolism showed that it generally matches to the pattern of
previously reported diatom metabolic networks. As well we found some hints regarding
Nitzschia external carbon acquisition which possibly can help to explain its heterotrophic mode
of life. Overall, this study has provided novel insights into the evolutionary origin and
metabolism of non-photosynthetic diatoms, which are unique among diatoms in their ability to
sustain their growth solely from extracellular carbon.
Onyshchenko, Anastasiia, "Phylogeny and Evolutionary Genomics of Non-Photosynthetic Diatoms" (2018). Theses and Dissertations. 2695.
Available for download on Wednesday, May 13, 2020