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Research Team
Research Team
Natalie Kiepert
Natalie Kiepert
Microbiology
Tharaka M Alagiyawadu
Tharaka M Alagiyawadu
Microbiology
Introduction
Introduction
About 25 million metric tons of road salt are applied to icy roadways in the United States every year.1
Road salts cause increased chloride levels in ponds and lakes, which scientists have linked to reduced ecosystem diversity and nutrient imbalances.3,4
Green algae are sensitive to high salinity but have mechanisms to protect against reactive oxygen species caused by salt stress.2,5
A previous study showed that photosystem II (PSII), a protein complex of the ‘light reactions of photosynthesis’, had increased protection under mixotrophic conditions where the cell gained energy through both photosynthesis and organic carbon in the form of acetate.5
Figure 1. Simplified model of the light reactions of photosynthesis demonstrating the role of photosystem II (PSII) in splitting water to provide protons and electrons for the remaining steps of the process.
Research Question
Research Question
Growing the freshwater green microalga Chlamydomonas reinhardtii under autotrophic conditions investigated the research question: how does PSII function under high salt stress in C. reinhardtii?
Methods
Methods
Figure 2. C. reinhardtii grown in batch cultures under controlled light and temperature.
Figure 3. Dual-PAM100 chlorophyll fluorometer measuring PSII activity in the algae lab.
Results
Results
Higher concentrations of NaCl correlated with lower optical densities and were soon to reach the death phase compared to cultures at lower salinities.
Fv/Fm generally decreased, Y(II) decreased, qL fluctuated and remained relatively constant, NPQ increased.
As salt concentrations increased, cells became less motile, losing their flagellum and forming aggregates and membrane-bound palmelloid structures.
Figure 4. Growth curve representing optical density at 750 nm of C. reinhardtii culture in media with salt concentrations ranging from 50-100 mM over the number of days grown in batch culture.
Figure 5. Growth rates of batch cultures in BBM with NaCl concentrations from 50-100mM based on optical density measurements at 750nm.
Figure 6. Graph of the four photochemical parameters monitored to assess PSII activity and stress.
Fv/Fm – PSII capacity
Y(II) – PSII activity
qL – Oxidizable PSII
NPQ – non-photochemical quenching
Figure 7. Images of normal mobile C. reinhardtii cells (left) compared to cells under salt stress (right) at 1000x magnification.
Conclusions and Future Study
Conclusions and Future Study
Higher salinity corresponded with reduced growth of C. reinhardtii.
Cultures in increased salt conditions tended to be more stressed and less efficient at performing PSII activity.
Palmelloid formation allowed cells to efficiently exchange nutrients under stress.
NaCl led to lower growth rates and increased stress on PSII; therefore, it would be expected that road salts would decrease PSII function due to stress.
Further investigation would be required to predict possible mechanisms used by C. reinhardtii to protect PSII under long term salt stress.
The following is an image of the poster presented at the 2026 Undergraduate Research Forum.
Acknowledgements
Acknowledgements
Many thanks to my mentors Dr. Rachael Morgan-Kiss, Dr. Devon Popson, and 4th year doctoral candidate Tharaka Alagiyawadu for their excellent guidance on experimental design, equipment operation, and data analysis. Funds from DOE Photosynthetic Systems (DE-SC0019464) and the Undergraduate Research Award 2025 have helped support the ongoing progress of this project.
References
References
Billau, C. (Dec 2021). Study shows critical need to reduce use of road salt in winter, suggests best practices. University of Toledo. Ecological Society of America.
Kalra, I., Wang, X., Zhang, R., and Morgan-Kiss, R. (8 Feb 2023). High salt-induced PSI-supercomplex is associated with high CEF and attenuation of state-transitions. Research Square. https://doi.org/10.21203/rs.3.rs-2557716/v1
Shantal, R. (Winter 2022). As salt coats snowy roadways in winter, freshwater ecosystems pay a heavy price. Audubon Magazine.
Sherwell, S. (Nov 2020). Winter is Coming! And with it, tons of salt on our roads. Southern New England Program (SNEP). United States Environmental Protection Agency. https://www.epa.gov/snep/winter-coming-and-it-tons-salt-our-roads
Wheeless, K.D. (2025). Mixotrophic growth leads to increased resistance of Chlamydomonas reinhardtii to abiotic stress [Master of Science Thesis, Miami University]. The Graduate School Miami University Oxford, OH.
Photo: The salty truth: How road salt affects your vehicle. Integrity Vehicle Production. https://www.integrityautowarranty.com/single-post/the-salty-truth-how-road-salt-affects-your-vehicle
NACE Career Readiness Competencies
NACE Career Readiness Competencies
Career + Self-development – explored the projects and seminars involved in grad school
Communication – grew in the ability to schedule lab time and seek out guidance from mentors on experimental design
Professionalism – respected other lab members by maintaining a safe, orderly lab environment
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