Understanding the metabolic pathways that microalgae undergo in photobioreactors to produce metabolites and biofuels is achieved by specific feeding regimes. Diatoms need silicic acid to create their silica cell wall, which is made during cell division. The deliberate addition of silicic acid controls cell division, henceforth the production of stress-induced metabolites. Nitrate is used by diatoms to produce cellular material and nitrogen bearing metabolites, such as chitin. Lipid production by diatoms is a way of energy storage.  Cell biomass, lipid and chitin productivity  by the marine diatom Cyclotella sp was studied in batch and perfusion feeding under sequential co-limitation of two macronutrients, silicon and nitrogen in a bubble column photobioreactor. During the cultivation  in the photobioreactors, the cell suspension was assayed for cell number density, dissolved silicon and nitrate concentrations in the media. In specific points of the experiment, biomass samples were analysed for lipid and chitin content.<br/>In the batch experiments, the co-limitation was carried out by increasing the initial nitrate concentration from 0.5 to 5.0 mM at a constant dissolved silicon concentration of 0.8 mM. In the perfusion feeding experiments, the initial silicon to nitrate concentration ratio (Si/N) is 0.7, and it is maintained throughout the perfusion, in silicon and nitrate starved environments.  The perfusion is carried out through sequential periods of time ranging from 2 to 21 days. In batch cultures, chitin is produced at Si depletion within the first 48 hours of stationary phase. The range of chitin production is 2 to 10 mg/ 100 mL of culture. Lipids production is induced at silicon depletion, and ranged from 10-15 wt% lipid in dry biomass. In the perfusion experiments, lipid production is stimulated to achieve 20 wt% lipid, and is turned off as the perfusion is extended to periods longer than 14 days. These results show that nitrate delivery at silicon limitation is the primary variable for the metabolic flux of chitin and silicon-nitrogen delivery in a silicon-nitrogen starved regimes through extended periods of time inhibits the metabolic production of lipids.

Stimulation of lipid and chitin production in the photosynthetic diatom <i>Cyclotella</i> by co-limitation of silicon and nitrate in batch and perfusion cultivation

249th National Meeting (2015)

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Stimulation of lipid and chitin production in the photosynthetic diatom Cyclotella by co-limitation of silicon and nitrate in batch and perfusion cultivation