Use of Bicarbonate Salts in Algal Growth for Enhancement of Lipid Content
Production of biofuel from microalgae has thus far been cost prohibitive due in part to expenses
associated with providing the necessary algal feedstock. In particular, inorganic carbon must be supplied
in higher concentrations than available atmospherically to achieve high density cultures necessary for
biofuel production strategies. Cost of algal biomass as a feedstock will be the most limiting factor to
realization of algal biofuels moving forward. Research has demonstrated bicarbonate supplementation
can enhance lipid content in select algal cultures when paired with stress conditions, such as nitrogen
limitation. This phenomenon is known as bicarbonate induced lipid accumulation and has unrealized
potential in executing economical algal biofuel production. Still, this method has only been demonstrated
in select microalgal species and relatively little metabolic information is available regarding its use. Here,
two species were investigated with the use of bicarbonate salts for algal growth and lipid accumulation.
Nannochloropsis gaditana is a marine microalga which produces high lipid content under nutrient stressed
conditions and has not been thoroughly studied with use of bicarbonate. This organism was studied under
bicarbonate supplementation in batch photobioreactor systems. Chlorella vulgaris is a fresh water green
alga which has received attention as a biofuel candidate due to high growth rates and lipid content. This
organism was investigated under bicarbonate supplementation during nitrogen depletion with the use of
high-resolution magic angle spinning (HR-MAS) 1H NMR spectroscopy over a 38-hour diel cycle. N.
gaditana showed highest growth rates under pH controlled growth during nitrogen replete conditions,
and bicarbonate amendments were seen to increase lipid content following nitrogen depletion when
paired with this growth strategy. However, N. gaditana demonstrated low productivity in batch systems
and may not be an ideal candidate for biofuel production as it has relatively low growth rates compared
to other industrially relevant organisms. NMR metabolite investigation in C. vulgaris revealed large
incorporation of inorganic carbon from bicarbonate amendments into biomass, observed as increases in
the biological sucrose pool and subsequent synthesis of fatty acid chains.
Use of Bicarbonate Salts in Algal Growth for Enhancement of Lipid Content, Thesis Defense by Todd
Pedersen, MS Candidate, Chemical and Biological Engineering, Montana State University, August 25,
2016.