The Diatom - Thalassiosira

By Allison Lee

About Thalassiosira

CLASS: Coscinodiscophyceae

ORDER: Thalassiosirales

FAMILY: Thalassiosiraceae

GENUS: Thalassiosira

Thalassiosira are a genus of centric diatom and primarily grow in marine waters. Most species are cosmopolitan, or able to exist in a variety of marine environments around the world. This genera comprise the largest of the centric diatoms with more than 100 species described.

They can be identified by their characteristic shape: box shaped, cylindrical, drum shaped, discoid, and coin shaped. To a trained microscopist, other readily recognized features such as strutted, occluded, and labiate processes can further distinguish specific Thalassiosira species.

Cells can be found as individual cells or in chains connected by organic threads.

History of Thalassiosira

Thalassiosira first appeared in the geological record 13.82 million years ago.

Thalassiosira pseudonana was chosen as the first eukaryotic marine phytoplankton for whole genome sequencing because of its relatively small genome (34 mega base pairs) and this species has served as a model for many diatom physiology studies. The specific culture that was sequenced came from CCMP 1335 from the Center for Culture of Marine Phytoplankton and was originally collected in 1958 from Moriches Bay (Long Island, New York).

How to grow Thalassiosira

The most important thing to remember for Thalassiosira cultures, is that they need silica to maintain their cell wall (or frustule). Most Thalassiosira cultures do well in a liquid culture medium of f/2-enriched seawater grown in a glass Erlenmeyer flask. They can be grown in plastic tissue culture flasks but a glass vessel increases their ability to scavenge silica off the flask wall.  Your cultures will be happy if they are grown in their preferred temperature range and receive gentle daily mixing.  They grow best under medium light levels (~150-300 μE m−2 s−1), and can photo bleach if exposed to high light or direct sunlight. A healthy culture can reach a carrying capacity between 1×105 and 2 x 106 cells/mL in laboratory cell culture setting.

If you're interested in purchasing a specific strain, look at any of the 89 Thalassiosira species available on the NCMA Bigelow Labs website.

When to harvest Thalassiosira

Depending on your uses, Thalassiosira is best harvested during mid to late exponential phase of growth. This can be estimated visually when cultures take on a golden hugh. This stage can also be measured when cells reach a Photosynthetic efficiency (maximal PSII quantum yield, Fv/Fm) of 0.6 and just before they’ve depleted their nitrogen source.  


Harris, A. S. D., Medlin, L. K., Lewis, J., & Jones, K. J. (1995). Thalassiosira species (Bacillariophyceae) from a Scottish sea-loch. European Journal of Phycology, 30(2), 117-131.

Spaulding, S., and Edlund, M. (2008). Thalassiosira. In Diatoms of the United States. Retrieved April 29, 2017, from

Tomas, C. R. (Ed.). (1997). Identifying marine phytoplankton. Academic press.

Images of Thalassiosira from the Encyclopedia of Life. Retrieved from