Date of Graduation


Document Type


Degree Name

Master of Science in Cell & Molecular Biology (MS)

Degree Level



Biological Sciences


Andrew Alverson

Committee Member

Jeffrey Lewis

Second Committee Member

Andy Pereira


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.

Appendix1.xlsx (24 kB)

Available for download on Wednesday, May 13, 2020