High-density heterotrophic cultivation of Galdieria sulphuraria for the production of high-stability phycocyanin

Phycocyanin is an important natural blue photosynthetic accessory protein-chromophore complex expressed by classes of cyanobacteria and Rhodophyta. This protein finds significant use in the food manufacturing industry as the only natural blue colour with global regulatory approval, as well as displaying nutritional value as a protein and nutraceutical benefits through its strong antioxidant capability. Despite this, end use in many applications is precluded by its limited stability when exposed to heat and light, a direct consequence of the narrow ecological niche of the organism it is currently produced at scale from, Arthrospira platensis. Our research focuses on production of phycocyanin from the thermoacidophilic Rhodophyte Galderia sulphuraria, which displays much improved stability profiles when exposed to high temperatures and low pH, a direct result of the volcanic hot acidic spring environment which may reach pH 0 and 55°C, and represents G. sulphuraria’s ecological niche. Important process characteristics are exemplified in this research in order to generate very high cell densities and phycocyanin productivities, above 40 g.L-1.day-1 and 1.7 g.L-1.day-1 respectively, more than double the previously reported highs. Oxygen saturation during semi- and continuous heterotrophic cultivations is identified as a key driver for phycocyanin productivity, and a series of specially adapted bioreactors are developed in order to achieve this parameter. New ways of controlling nitrogen in the process and its implications on production are investigated, along with developing sterility into a heterotrophic process without the high cost of autoclaving requirements. These techniques are successfully applied to abundant problematic industrial waste streams – unrefined biodiesel-derived glycerol and lignocellulosic biomass, harnessing the extremophilic nature of G. sulphuraria and its propensity to grow on a diverse range of organic carbon substrates. Learnings from the development and in-house fabrication of specialised equipment for such an extremophile are detailed, including the adaptation of modern engineering plastics, recent availability and suitability of ad hoc microcontroller systems in the context of simple, high-density, high-productivity algal cultivation.