Cyanobacterial phycobilins: Production, purification, and regulation

Abstract

The cyanobacteria are a diverse group of prokaryotic organisms that carry out oxygenic photosynthesis and are thought to be responsible for the oxygenation of our atmosphere. Like red algae and cryptomonads, cyanobacteria also contain phycobiliproteins (PBPs) which serve as major accessory pigments during photosynthesis. PBPs are large water-soluble supramolecular protein aggregates involved in light harvesting and can be divided broadly into three classes, viz., phycoerythrin (PE), phycocyanin (PC), and allophycocyanin (APC) based on their spectral properties. PBPs have been extracted and purified from Spirulina spp., Synechococcus sp., Oscillatoria sp., etc., and produced commercially from Spirulina platensis, Anabaena sp., and Galdieria sulphuraria. Since cyanobacteria exhibit wide variations in nutrient availability, light intensity, light quality (wavelength), temperature, water activity, etc., these variations also result in altered metabolic activity of these organisms as a result of differential expression of different genes. The expression of phycobiliprotein coding genes is also accordingly modulated to adapt to a particular condition. Many workers have reported changes in phycobilisome structure and expression of cpc genes in response to light quality, light quantity, and nutrients like nitrogen, sulfur, etc. The composition and function of phycobiliproteins in cyanobacteria have also been reported to change under stress conditions. In the present paper, we have reviewed the production, purification, and regulation of cyanobacterial phycobilins including their importance in the commercial sector, as they have several applications as natural dyes in food and cosmetic industry, immunological assays, healthpromoting properties, and broad range of other pharmaceutical applications.