**4.1 Color sensing by Cphs and CBCRS**

Cyanobacterial proteins contain the accompanying regions PAS-GAF-PHY [48]. Entire genome sequencing of cyanobacterial species, for example, *Microcoleus* IPAS B373 [49], *Euhalothece* Z-M001 [44], and *Tolypothrix* PCC7910 [50] are devoid of gene HY2, for phytochromobilin (PФB) synthase. Further, these cyanobacteria have pcyA gene that encodes phycocyanobilin (PCB): ferredoxin oxidoreductase that catalyzes the conversion of biliverdin (BV) to PCB, a significant cofactor of Cphs and CBCRs [32, 51]. The quantity of Cphs and CBCRs differ among cyanobacteria, *Euhalothece* has 3 numbers, *Synechocystis* (8), *Microcoleus* IPAS B353 (9), *Acaryochloris marina* (12), *N. punctiforme* (18), and *Tolypothrix* PCC 7910 (36). In cyanobacterium, the complete number of bilin photoreceptors relies upon the size of its genome [49]. Besides, CBCRs are more plentiful in cyanobacteria, than Cphs, and the proportion of CBCRs for blue to red is corresponding to the environmental light conditions. For example, *Microcoleus* IPAS B353 grown in UV light developed only violet CBCRs than red/green and green/red CBCRs. Generally, UV light is recommended to develop and improve the quantity of short wavelength responsive CBCR [49].
