Effect of organic carbon source and nutrient depletion on the simultaneous production of a high value bioplastic and a specialty pigment by Arthrospira platensis

Abstract

Many studies have shown enhanced production of single high value products from microalgal cultivation can be achieved by employing nutrient limitation and/or organic carbon supplementation. The possibility of exploiting multiple high value microalgal biosynthetic products has rarely been examined, even though it is widely acknowledged that such systems are likely to improve the economics of chemical production from this source. The co-production of two high value microalgal products, phycocyanin and polyhydroxybutyrate (PHB), was investigated under photoautotrophic and mixotrophic conditions, with and without nutrient limitation, in Arthrospira (Spirulina) platensis MUR126 cultures. Cultures accumulated PHB under nutrient replete phototrophic conditions while maintaining phycocyanin levels. Supplementing Arthrospira platensis cultures with additional CO2 increased PHB (33% at day 14), biomass (23 %) and phycocyanin productivity (30%). The results from cultures grown mixotrophically using organic carbon sources commonly found in agricultural and industrial waste streams (acetate, formate, glycerol and oxalate), and under nutrient limitation, did not show a definitive trend. When Arthrospira platensis was cultured in media devoid of both N and P, supplementing with glycerol and acetate led to a significant increase in biomass productivity compared to a photoautotrophic reference culture, but negatively affected both phycocyanin and PHB production. The poor co-production results for Arthrospira platensis under mixotrophic conditions suggest that a minimum level of N is required to maintain phycocyanin levels and a greater concentration of the organic C source is needed to create a redox balance within the cells that enhances PHB production.