What makes algae reproduce sexually?
Microbiologist Kimberly Halsey discusses the accidental discovery of sexually reproducing diatoms in her lab.
Vocabulary: diatom, asexual reproduction, sexual reproduction, cell division
Next Generation Science Standards: SEP1- Asking Questions and Defining Problems, CC2- Cause and Effect: Mechanism and Explanation, LS1.B: Growth and Development of Organisms, and LS3.A: Inheritance of Traits.

Diatoms are a type of single-celled algae found all over the world. Considered model organisms, they’re a staple in labs studying ocean water quality. Indeed, they’re as ubiquitous in microbiology research as lab mice are in human-health studies.
Diatoms are so well-studied that some facts about them seem irrefutable, like their asexual method of reproduction by cell division. But by happy accident, researchers at Oregon State University recently discovered a group of centric diatoms that reproduce sexually when stimulated by the presence ammonium in the surrounding water. Kimberly Halsey, an assistant professor in the Department of Microbiology at Oregon State University, joins Ira to discuss how scientists overlooked something so fundamental about an organism they thought they knew so well.
Print this segment transcript.
Questions
- These particular diatoms usually reproduce asexually, through cell division. Describe the difference between the genes of the offspring of sexual versus asexual diatom reproduction.
- There were already rare glimpses of diatom sexual reproduction in the wild. How does this discovery further the field of study into diatom sexual reproduction?
- Why are diatoms such an important part of the ocean ecosystem?
- Based on the interview, create an illustration that depicts the process of discovery for Eric Moore and Kimberly Halsey. Be sure to depict the whole process from the diatom culture media to triggering sexual reproduction with ammonium.
“The most exciting phrase to hear in science, the one that heralds the most discoveries, is not “Eureka!” (I found it!) but “That’s funny…” — Isaac Asimov
- Explain how the phrase above relates to Kimberley Halsey and Eric Moore’s research on diatoms.
Activity Suggestions
- Explore the biology of aquatic plants like diatoms with this activity where you grow algae in a bottle and look at the effect of nutrients and light levels on growth. Have students go further by relating this experiment back to the one done in the interview. Can they create a new experiment by incorporating the variable they investigated with their bottle(light and/or nutrients) into the research on diatom sexual reproduction done by Kimberly Halsey’s lab?
- Have students take a deeper look at the role of diatoms in the ecosystem with this activity focused on Great Lakes ecology. You can also have students use the Food Chain Checkers activity to model the dynamics of a simple food chain that includes orca, herring, copepods, and diatoms.
Additional Resources
Check out this sand under a microscope. Can you spot the diatoms in the sand?
Check out the original paper! Moore ER, Bullington BS, Weisberg AJ, Jiang Y, Chang J, Halsey KH (2017) Morphological and transcriptomic evidence for ammonium induction of sexual reproduction in Thalassiosira pseudonana and other centric diatoms. PLoS ONE 12(7): e0181098.


