Characterization of Chlorella munitissima cell wall under mixotrophic growth conditions

Microalgae have been considered as an alternative fuel source due to their high lipid content, fast growth rates, and ability to be cultivated on wastewater. This study focuses on mixotrophic growth conditions, specifically glucose, glycerol and acetate as carbon sources, which emulate substrates algae may encounter when grown in wastewater systems. In order to recover intracellular products accumulated by algae, such as lipids and polysaccharides, effective cell lysis method need to be developed. Furthermore, if algae are to be considered for biofuel production and since the cell wall can be as much as 16% of biomass by dry weight when grown under mixotrophic growth conditions, products from the cell wall need to be identified. However, the cell wall compositions under these growth conditions were not known, making the identification of resource efficient lysis methods and use of cell wall biomass difficult. The aim of this project was to characterize the complex carbohydrate monomers of Chlorella minutissima cell walls using trimethylsilyl (TMS) derivatization methods. After growth in a mixotrophic batch reactor, the algae were lyophilized, defatted, and enzymatically digested for the removal of starch. The remaining biomass was derivatized by the TMS method and analyzed using a quadrupole gas chromatography/mass spectrometry (GC/MS). TMS derivatization allows detection of neutral, amino, and acidic sugars by GC/MS, mass balance, and identification of novel sugars. Using this method, the cell wall carbohydrate components were identified.   Results will be used to propose cell wall lysis strategies and biomass uses.