Understanding How Varying Conditions Affect Growth Rates of an Unidentified Diatom-Diazotroph Association Symbiosis
Major
Marine Biology
Minor(s)
Chemistry
Advisor
Tatiana Rynearson
Advisor Department
Oceanography, Graduate School of
Date
5-2025
Keywords
Biological Oceanography; Diazotroph; Symbiosis; Phytoplankton; Temperature
Abstract
In the ocean, bacterial diazotrophs can exist in symbiosis with eukaryotic phytoplankton called diatoms. These Diatom-Diazotroph Associations (DDAs) are important due to their niche expansion of diatoms that allows for more carbon export in oligotrophic regions, but little is known about their biology because they are rarely brought into culture. This project investigated a diatom collected in the summer of 2023 from the Northeast US Shelf that is able to grow in nitrogen free media, leading us to believe that it must be living in association with a diazotroph. The goals of this project were to understand how temperature and presence of the fixed form of nitrogen nitrate affect the growth rate of this DDA, and to identify the diatom species in culture. From March to May 2025 growth rates were calculated across varying temperatures and nitrogen availability using cell counts on an inverted microscope and in vivo chlorophyll fluorescence using a fluorometer. In addition, DNA extraction and sequencing were utilized to determine the identity of the diatom. In general, growth rates were slow (0.13 day-1) and varied slightly across temperature and nutrient source. Based on our results thus far, the cells have faster growth rates in nitrogen free media. This project was able to identify the diatom species and has expanded our knowledge of the types of diatoms that grow in a symbiotic relationship with nitrogen fixing organisms.