# The Effect of LEDs on Biomass and Phycobiliproteins Production in Thermotolerant _Oscillatoria_ sp.
## 4 Discussion
In this case, the purity for C-PC, APC, and PE is statistically higher than the control (fluorescent lamps), indicating a balance between biomass building up and synthesis of PBPs; moreover, there are few cases reported in the literature that can support these results. [PERSON] et al. [59] found that biomass and C-PC content can be improved when _A. platensis_ is grown in a two-stage process. In this case, they tested red/blue LEDs (1:1) for biomass production, followed by a second stage using blue LEDs to increase the synthesis of C-PC; however, there was no evidence of the effect of mixing white light with other LEDs. Other factors such as light intensity and photoperiod (also known as light:dark cycle) are as important as the quality of light [53]. [PERSON] et al. [72] found out in their preliminary experiments that a thermotolerant _Leptolyngbyu_ sp. strain could not grow normally at high radiations (up to 2800 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\)) due to their lack of adaptation. Therefore, the low biomass concentration of _Oscillatoria_ sp. at elevated radiation requires acclimization since this strain was isolated from a hot spring in Colombia with high radiation. For the case of the photoperiod, longer light times favor photosynthesis, and by adjusting the intensity and wavelength, it is possible to increase biomass concentration; however, this interaction between the light cycle and intensity may depend on the strain evaluated. In the case of _A. maxima_, when growing under medium intensities (80 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\)) with white LED lights and complete exposure to light (24 h), it is possible to obtain more biomass compared to blue or orange LED lights [50]; for the case of _A. platensis_, blue light with the same conditions mentioned above are the ones that favor its growth. In another work, [PERSON] et al. [55] demonstrated yellow LEDs lights with an intensity of 250 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\). A cycle of 12 h light and 12 h dark can maximize the biomass of _A. platensis_ by up to 6.6 g/L, which is much higher than that found by [PERSON] et al. [39] (0.59 g/L) or [PERSON] et al. [54] (8.95 g/L). Another example of this is the results achieved by [PERSON] et al. [25] by using _Synechococcus_ PCC 6715 (red LEDs, 100 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\), and 16 h of light and 8 h of dark), which achieved the highest concentration reported for research of this type (8.6 g/L) and is even more interesting since no inorganic carbon sources were used in the BG11 medium. According to different articles published internationally in recent years, the effect of the parameters mentioned above on the synthesis of phycobiliproteins does not follow a fixed pattern [73; 74; 75]. Therefore, strains of the same species may have different light requirements. This can be explained by the unique composition of PBPs of each cyanobacterial strain. This would explain the unusual behavior of _Oscillatoria_ sp., which not only has high concentrations of C-PC but, under certain conditions, the concentration of PE increased significantly compared to the control. It is worth mentioning that the short distance between the light source and the small diameter of the flask is a variable that must be considered in the selection of the culture method (raceways, column, or tubular PBR) for a scaling process.