Effect of dilution rate in continuous cultures of Arthrospira (Spirulina) platensis C1 on nutrient use efficiency and macromolecular- and elemental compositions

Abstract

Arthrospira (Spirulina) has potential applications as food supplements, feeds, pharmaceuticals, and biofuels; but its production process is inefficient. To maximise biomass production and nutrient use efficiency of Arthrospira, steady-state data from continuous cultures provides a unique means of productivity optimisation. In this study we cultivated the cyanobacterium Arthrospira (Spirulina) platensis C1 in a helical tubular photobioreactor initially in batch cultures, by independently investigating pH control, light intensity, and temperature, to optimise specific growth rate (μ) and biomass productivity. Optimal growth was achieved at 200 μmol photons m−2 s−1, 35 °C, and without pH control. Arthrospira was then grown in continuous culture at four different dilution rates (D: 0.0087, 0.0173, 0.0287, and 0.0324 h−1). Macromolecular and elemental compositions of biomass were determined, and both nutrient consumption rates and biomass yields at each D were calculated. Protein composition of the biomass was found to be highest (62.21%) at the lowest D, while the compositions of lipid, RNA, and DNA increased with the increasing D. Results from the continuous culture experiments also suggested that nutrient utilisation was best at lowest D, but cells grown at intermediate D had the greatest biomass yields and highest biomass productivity. Nutrient use efficiency analysis confirmed that cells converted nutrients into biomass most efficiently when cultivated at intermediate D. Results from the continuous culture experiments provide much-needed fine-tuned growth and productivity optimisation of Arthrospira cultures and may be used for a refinement of a genome-scale metabolic model of Arthrospira and flux balance analysis research in the future.