Effect of a dark-colored substrate on the production of phycocyanin by the cyanobacterium Phormidium sp

As the biotechnological production of valuable compounds has recently gathered research interest, more and more photosynthetic microorganisms are being examined for the synthesis of proteins, fatty acids, pigments, and other biopolymers. In this work, a local isolate (lagoons of Western Greece), of the blue-green cyanobacterium Phormidium sp., was evaluated. Its cultures were considered to be promising for the recovery of the phycobiliprotein, called phycocyanin, even during mixotrophic growth. Interestingly, phycocyanin accumulation was favored by substrates with a low organic load. In order to minimize substrate cost, anaerobic digestion effluent was used as a nutrient and organic carbon source, replacing a synthetic medium containing glucose, to meet the cyanobacterium's nutrient needs. The results from the cultures containing liquid digestate were surprising, as its addition at low concentrations not only allowed Phormidium sp. to grow but also enhanced the phycocyanin synthesis. The experiments that exhibited a notable phycocyanin production showed a final biomass concentration that barely exceeded 0.7 g L-1 regardless of the nature of the substrate. When Phormidium sp. was inoculated in a pure synthetic medium with 1 g L-1 of glucose, phycocyanin concentration approached 10 mg L-1, while it was measured being 1.75 times higher in the culture containing 10% v/v anaerobic effluent, due to greater cellular accumulation. The present work comes as evidence of the successful bioremediation of digestate accompanied by the production of a high added-value pigment, leading to the removal of organic carbon, total nitrogen, and phosphorous in percentages of 60%, 90%, and 40% respectively.