PS 81-208
A sustainable method for carbon sequestration using algae (Chlamydomonas reinhardtii) deficient in phosphate and nitrogen uptake

Thursday, August 13, 2015
Exhibit Hall, Baltimore Convention Center
Nikhil S. Gopal, Student, The Lawrenceville School, Lawrenceville, NJ
Background/Question/Methods: Carbon dioxide levels have been rising rapidly. Algae are single celled protists with highly efficient CO2 uptake mechanisms. Algae yield 2-10x more biomass vs terrestrial plants and can grow nearly anywhere. Large scale CO2 sequestration is not yet sustainable due to high amounts of nitrogen (N) and phosphate (P) needed for growth media. Objective: was to see if mutant strains of algae could be created that were deficient in N/P uptake but produced as much biomass as control strains. To conduct the experiment, I created two new mutant strains of C reinhardtii using ultraviolet light (2.2-3K J/m2) and natural selection with lower concentrations of N/P based Sueoka’s media (20-80% normal). Biomass was compared to wild-type control (CC-125) using direct counts, optical density and dry weight. Mean doubling time also was calculated.

Results/Conclusions: Mean doubling time was 20 and 25 hrs in the Low N and Low N/P strains respectively (vs 66 hrs in control). Dry weight and optical density measurements had fair-poor correlation to cell counts (R2 = 0.1 and 0.6) respectively. Using direct counts, growth rates of mutant strains of Low N and Low N/P cultures were not significantly different from control (P = 0.37 and 0.70) respectively. Growth was best in 80%N/80%P and 80%N/60%P media. My new strains of algae were able to grow as well as wild-type control while using 20-40% less N and P. Implications for ecology: it has been estimated that algae could capture 95 million tons CO2/ha/year. Using my strains an extra 19-38 million tons CO2/ha could be captured/year. This may make long-term CO2 sequestration using algae more sustainable.