Carbon source-mediated metabolic and bioprocess optimization for C-phycocyanin enrichment in Phormidium sp. A02 under two-phase static mixotrophic culture.

Abstract

C-Phycocyanin (C-PC), a fluorescent photosynthetic protein derived from cyanobacteria, is used in the food, cosmetic, pharmaceutical, and biotechnology industries. Various cyanobacterial sources of C-PC have been studied to harness its biological functions such as antimicrobial, antioxidant, anticancer, and anti-inflammatory properties. Phormidium sp. A02 isolate from the Indian coast was cultured in a mixotrophic static environment to determine the effect of various bioprocess parameters like culture medium and light (photoperiod, light intensity, and light color) on biomass productivity and C-PC content. The C-PC from Phormidium sp. A02 can be used in the food and cosmetic industry as an alternative to synthetic chemical colorants. Carbon-mediated metabolic engineering of C-PC in Phormidium sp. A02 using Guillard's F/2 seawater medium supplemented with carbon sources like glucose, sucrose, glucose + peptone, and sucrose + peptone was carried out to determine its growth and C-PC enhancement efficiency. Sucrose + peptone with C/N ratio 4.76 increased Phormidium sp. A02 biomass productivity (0.197 ± 0.02 g dry weight L^-1 day^-1) by twofold compared to the autotrophic control (0.105 ± 0.01 g dry weight L^-1 day^-1). An analysis of C-PC content enhancement with glycerol supplementation showed that 0.9 g of glycerol L-1 was the optimal concentration. Higher biomass productivity (0.176 ± 0.01 g L^-1 day ^-1) was observed in photoperiods of 8/16 h light/dark and higher C-PC content (69.91 ± 4.86 mg g^-1) at lower light intensity in Phormidium sp. A02 under mixotrophic conditions. A two-phase static culture strategy was developed, beginning with 5 days of initial biomass production under white light, followed by 3 days of C-PC enhancement under monochromatic light. The dry biomass production in sucrose + peptone under white, green, and red light was similar in our two-phase static culture strategy, averaging 0.27 g L^-1. In contrast, red light induction increased C-PC more than other lights and by 6.5-fold (52.30 ± 0.002 mg g^-1) over a control with white light (7.76 ± 0.58 mg g^-1). C-PC had thermal stability up to 55 °C, pH stability up to 4.00 and a purity of 0.69. Phormidium sp. A02 cultured in a closed system under bioprocess strategies such as red-light induction, glycerol supplementation, and metabolism switchover could enhance C-PC and make it a viable culture technique.