# The Effect of LEDs on Biomass and Phycobiliproteins Production in Thermotolerant _Oscillatoria_ sp.
## 1 Introduction  
Cyanobacteria are potential producers of value-added bioactive compounds such as chlorophyll a, b and c; \(\beta\)-carotene; astaxanthin; xanthophyll; and phycobiliprotein [1]. Most of the bioactive compounds isolated from cyanobacteria consist of amino acids and fatty acids and antibacterial, antifungal, anti-algal, antiprotozoan, and antiviral agents [2, 3, 4, 5, 6]. Phycobiliproteins (PBPs) are a group of brilliant water-soluble pigment proteins found in cyanobacteria and red algae [7]. These proteins are divided according to their color into blue (phycocyanin or C-PC), blue-green (allophycocyanin, or APC), and pink-purple (phycoverthrin, or PE) [8]. This group of proteins is exploited as colorants for the food industry (desserts, gums, gelatins, ice cream), pharmaceuticals (eyeliners, lipsticks, and makeup), and even in the development of anticancer agents [9, 10]--with a market price of up to 1500 USD per mg (highly purified phycobiliprotein) [11]. The number of strains that are industrially produced is limited to a handful of genera (such as _Anabaena_ sp., _Nostoc_ sp., _Plormidium valderianum, Porphyridium cruentum, Spirulina platensis_, and _Galdieria sulphuraria_) [12, 13, 14], with only one strain (_G. sulphuraria_) isolated from a thermophilic environment [15, 16, 17]. Thermal environments are the new frontier for isolating novelcyanobacterial strains with unique characteristics [18]; however, several culture parameters must be defined before exploiting novel strains [19; 20; 21; 22]. As photosynthetic microorganisms, light is one of the most critical factors during microalgae and cyanobacteria production [23]. Light wavelength and light intensity affect cell growth and pigment composition [24; 25; 26; 27; 28]. In the case of cyanobacteria, they are known for arranging their pigmentation to a specific light source to optimize light harvest [29]. Therefore, the understanding of light on the growth and deposition of metabolites is crucial for improving their production [30]. Most microalgal and cyanobacterial cultures employ sunlight; however, to produce specific metabolites (astaxanthin, lutein, and phycobiliproteins), most companies prefer controlled environments to maximize the synthesis of those metabolites [23; 31]. Typically, those specialized environments employ fluorescent lamps, but the companies have switched to light-emitting diodes (LEDs) [32]. LEDs are a sustainable alternative since they consume less energy, have a higher energy conversion efficiency, and last longer than traditional fluorescent lamps [33; 34; 35]. Unlike fluorescent lamps, LEDs can produce a specific wavelength with better quality, favoring the synthesis of specific metabolites such as photosynthetic colorants (carotenoids, chlorophylls, and phycobiliproteins) [30]. Worldwide, most algal production facilities use sunlight as the main light source; however, to improve production efficiency and avoid negative environmental conditions (such as winter), several companies are using LEDs as a more viable light source. Over the years, evaluating LEDs in phycocyanin production has gained momentum as an interesting tool for improving their synthesis [36; 37; 38; 39; 40; 41; 42; 43; 44; 45]. Several wavelengths (colors) such as white [46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 63], red [23; 25; 26; 26; 27; 28; 29; 30; 51; 52; 53; 54; 57; 58; 59; 63], and blue [59; 53; 57; 58; 59; 40; 53; 57; 59] have been studied. In the last ten years several strains have been studied using LEDs, including _Arthorspira_ sp [23; 47; 48], _A. maxima_[30; 49; 50], _A. platensis_[50; 51; 52; 53; 54; 56; 57; 58; 59; 60; 61], _Chlorogoelopsis fritschii_[62], _Cyanobium_ sp. [45], _Gracilaria tikuhaie_[63], _Porphyridium purpureum_[64], and _Synchococcus_ PCC 6715 [25].