# Indole-3-Acetic Acid Action in Outdoor and Indoor Cultures of _Spirulina_ in Open Raceway Reactors
## 4 Discussion
Nevertheless, notwithstanding the diminished protein concentration observed in the IAA-supplemented conditions compared to the control conditions, the protein productivity exhibited a contrary outcome. This divergence is attributed to the augmented biomass productivity facilitated by the presence of the phytohormone in the culture, which offsets the lower protein content. Similarly, in line with the investigations by [PERSON] [54] and [PERSON] et al. [61], variations in the experimental conditions did not induce alterations in the lipid content of the microalgal biomass. These authors substantiate that while temperature and illuminance exert a substantial impact on protein and carbohydrate composition, they do not exert a discernible influence on lipid production in _Spirulina_ biomass. Additionally, it is worth noting that supplementation with IAA at a concentration of 0.1 mg L\({}^{-1}\) did not yield a significant increase in lipid content in _Spirulina_ sp. LEB 18, as evidenced by the findings of [PERSON] et al. [16]. In contrast to findings reported in the prevailing literature, the introduction of phytohormone supplementation did not yield an observable enhancement in the production of the pigment phycocyanin [63; 64; 65; 66; 67]. Nevertheless, experiments conducted under outdoor conditions demonstrated higher phycocyanin yields than their indoor counterparts. Hence, the confluence of environmental factors may engender shifts in the microalgae's biochemical composition, potentially augmenting or diminishing the proportion of phycocyanin [68]. Moreover, there is a suggestion of a total or partial correlation between maximum biomass concentration values and phycocyanin content in _Spirulina_ cultures, as observed by [PERSON] et al. [69], [PERSON] et al. [70], and [PERSON] et al. [61]. This further underscores the ability of cyanobacterial cells to modulate their photosynthetic efficacy by modulating pigment production levels [71]. Despite the augmented expenses incurred by the incorporation of phytohormones into the growth medium for microalgal cultures, extant research posts that judicious adjustments in supplementation and cultivation methodologies may yield cost savings while concurrently augmenting biomass and biomolecule output [15; 16; 24; 38; 72]. The accomplishment of a cost reduction exceeding fifty percent in the production of biomass and biomolecules constitutes a significant milestone. Notably, the available data indicate that numerous global companies are actively conducting experiments aimed at cost reduction while maintaining the photosynthetic efficiency in _Spirulina_[3]. Furthermore, cultivating microalgae in an outdoor environment utilizing raceway-type reactors confers the advantage of obviating the need for artificial lighting and aeration. This strategic choice aligns with sustainability principles and reduces energy consumption, making microalgal cultivation more economically viable and environmentally sustainable. Although IAA is considered a high input, the increased production of biomass and biomolecules generated by supplementation makes its use advantageous. In this study, we used a small concentration to stimulate these effects. Thus, the cost of the cultivation medium was not increased significantly. It is essential to highlight that the microalgae, type of phytohormone used, supplementation concentration, and cultivation method, among other parameters, must be considered for the best cost-benefit of using the strategy. An additional noteworthy aspect is that adopting phytohormones as a strategy does not necessitate structural overhauls within the industry. Reactors like those employed in this study, specifically raceway-type open reactors, are extensively utilized for commercial microalgae production due to their lower construction and operational expenses than enclosed systems [26]. This approach aligns well with industry practices and can be readily integrated without significant modifications.