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Abstract
The microalga Botryococcus braunii is widely regarded as a potential renewable and sustainable source for industrial applications because of its capability to produce large amounts of metabolically expensive (exo-) polysaccharides and lipids, notably hydrocarbons. A comprehensive and systematic metabolic characterization of the Botryococcus braunii race A strain CCAP 807/2 was conducted within the present study, including the detailed analysis of growth-associated and physiological parameters. In addition, the intracellular metabolome was profiled for the first time and showed growth- and product-specific fluctuations in response to the different availability of medium resources during the cultivation course. Among the identified metabolites, a constant expression of raffinose was observed for the first time under standard conditions, which has until now only been described for higher plants. Overall, the multilayered analysis during the cultivation of strain CCAP 807/2 allowed the differentiation of four distinct physiological growth phases and revealed differences in the production profiles and content of liquid hydrocarbons and carbohydrates with up to 84% of organic dry weight (oDW). In the process, an enhanced production of carbohydrates with up to 63% of oDW (1.36±0.03 g L-1) could be observed during the late linear growth phase, whereas the highest accumulation of extracellular hydrocarbons with up to 24% of oDW (0.66±0.12 g L-1) occurred mainly during the stationary growth phase. Altogether, the knowledge obtained is potentially useful for the general understanding of the overall physiology of Botryococcus braunii and provide important insights into the growth behavior and product formation of this microalga, and is thus relevant for large scale biofuel production and industrial applications.
Highlights
Renewable and sustainable energy sources from photosynthetic microalgae are gaining increasing attention in recent years [1,2]
The measurement of total elemental carbon and nitrogen content in B. braunii CCAP 807/2 cell biomass revealed that the C/N ratio remained constant with a value of up to 10 between days 3–9 (Fig 1D), indicating that the cells did not suffer any nitrogen limitation [45]
The concentration measurements of the nitrogen source (KNO3) in the culture supernatant during the cultivation revealed that the major portion of nitrogen in the culture media was absorbed by the cells already after 9 days (Fig 1D)
Summary
Renewable and sustainable energy sources from photosynthetic microalgae are gaining increasing attention in recent years [1,2]. Because of its almost unique ability to synthesize large quantities of (exo-)polysaccharides and hydrocarbons and to secrete the latter [3,4,5], this colony forming green microalga represents a potential source for industrial applications like biofuels and other valuable chemicals [6,7]. B. braunii is well known to synthesize large amounts of polysaccharides, which represent the components of the cell wall and the retaining wall/ fibrillar sheath [8,18]. During the growth of B. braunii cultures, uniform cup-shaped structures, called “shells”, which represent excised segments of the retaining wall and its fibril sheath, are accumulating in the surrounding media and causing viscosity increase of the culture [3,8,19]
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