<i>Arthrospira platensis</i> Variants: A Comparative Study Based on C-phycocyanin Gene and Protein, Habitat, and Growth Conditions

This study aimed to map the differences between <i>Arthrospira</i> sp. and <i>Arthrospira platensis</i> strains and variants from the order Oscillatoriales at the gene and protein levels of C-phycocyanin alpha chain via multiple alignment, phylogenetic trees of species, and analysis of the nucleotide and amino acid composition of the studied sequences. The links between gene/protein and environmental features of the habitat or source of isolation were also investigated. Phycocyanin was extracted from three <i>A. platensis</i> strains: an Egyptian isolate cultivated in the laboratory under static conditions in a highly saline medium and two commercial products. The French commercial strain showed the highest extraction yield but the lowest C-phycocyanin purity, and the color intensity of the extracted pigment from the Egyptian isolate was significantly weaker than those of the two commercial strains. All the analyzed species and strains had GC content of more than 54.5% in C-phycocyanin alpha chain gene and showed high abundance of alanine, an amino acid encoded exclusively by GC-biased codons, in their protein. The frequencies of the acidic amino acids aspartic acid and glutamic acid were 5.2% and 5.0% on average, respectively, which were slightly higher than those of the basic residues (4.3% arginine, 0.6% histidine, and 5.0% lysine). Data relating to the isolation source of most of the analyzed species revealed harsh conditions, such as high alkalinity, salinity, CO₂ saturation, and/or temperature. These findings may link the gene/protein of C-phycocyanin, which is one of the most important bioactive proteins of <i>A. platensis</i>, to the adaptation of this organism to harsh environmental conditions and associate the color of the pigment to cultivation conditions and/or isolation source.