Cyanophycin production in turbidostat cultivation of cyanobacteria under phosphorus limitation on synthetic urine media

Abstract

The cyanobacterium Synechocystis sp. PCC6803 is capable of using ammonium as nitrogen source which is the main nitrogen compound present in source-separated urine. Under phosphorus limiting conditions, Synechocystis has the ability to accumulate nitrogen in form of cyanophycin, an interesting polymer for the industry of bioplastics with a wide range of potential applications in biotechnology and agroindustry. We studied the accumulation of cyanophycin in Synechocystis cultivated in nutrient supplemented synthetic urine using ammonium as nitrogen source with different concentrations of phosphorus in batch and turbidostat cultivation. A decrease in biomass yield on light was observed in the turbidostat cultivation under strong phosphorus limitation, accompanied by overproduction of carotenoids and accumulation of cyanophycin. Synechocystis accumulated increasing amounts of cyanophycin reaching 10% of dry weight in form of cyanophycin in batch mode cultivation, and 7% in turbidostat cultivation. Higher accumulation of cyanophycin in both, batch and turbidostat cultivation, occurred at the lowest phosphate availability, biomass productivity decreased under strong phosphorus limitation. Mild phosphorus limitation allowed both cyanophycin and biomass production in turbidostat cultivation, and gave the higher titers in batch cultivation and the highest productivity in turbidostat cultivation. Strong phosphorus limitation decreased productivity of both biomass and cyanophycin as well as the nitrogen content in the biomass.