Diatom Growth: East Coast Vs West Coast Challenge

The centric diatom Cyclotella cryptica is a microalga of considerable industrial and scientific value, owing to its metabolic versatility for both autotrophic and heterotrophic growth. Its capacity to produce high levels of lipids and the essential omega-3 fatty acid, eicosapentaenoic acid (EPA), makes it a prime candidate for producing biofuels and advanced nutraceuticals. However, achieving economically viable, large-scale cultivation is currently hindered by the challenge of formulating an optimal growth medium. Our previous work, which aimed to optimize an artificial seawater medium by assessing silicate concentrations from 0.5 to 5 times that of standard Guillard’s f/2 medium, revealed a significant performance gap: cultures grown in natural seawater from Boston Harbor consistently demonstrated superior growth compared to any synthetic formulation.

This performance disparity suggests that current artificial media fail to replicate essential components present in natural marine environments. Our study, therefore, investigates a fundamental question: do the distinct compositional profiles of major ocean basins influence diatom growth? We hypothesize that the nutrient-enriched waters of the Pacific Ocean will foster a higher growth rate and final biomass density for C. cryptica. This hypothesis is based on known oceanographic differences: the Atlantic’s higher salinity (35-37 PSU) versus the Pacific’s (34-36 PSU), and more critically, the Pacific’s nutrient-enriched state resulting from the global ocean conveyor belt. Our experimental design involves a three-week controlled trial where triplicate C. cryptica cultures are grown in three media: Atlantic seawater, Pacific seawater, and an artificial seawater control (28 g/L sea salt in DI water) supplemented with Guillard’s f/2 medium. Weekly water changes will maintain nutrient levels, and growth will be tracked by taking optical density readings every three days.

Building on these findings, future work will focus on optimizing the complete production pipeline. First, to maximize lipid content, we will implement a two-phase cultivation sequence, beginning with a nutrient-replete phase to encourage biomass accumulation, followed by a nutrient-deplete phase under light and 10% CO2 (v/v) bubbling to induce lipid synthesis. Second, we will develop an effective downstream protocol for lipid extraction and purification. This work will evaluate methodologies including liquid-liquid extraction for initial recovery, thin-layer chromatography (TLC) to separate lipids into desired classes, and gas chromatography (GC) to quantify the fatty acid profile and determine the final yield of EPA, a compound known to reduce inflammation and improve cardiovascular and brain health. By systematically optimizing cultivation and extraction protocols, this research aims to unlock the full potential of C. cryptica as a sustainable industrial platform.