## 1 Introduction  
According to a recent United Nations (UN) report, the global population is expected to increase from 7.7 billion to 9.7 billion by 2030, requiring a 60% increase in food production [1]. Proteins are an essential part of human nutrition and are expected to increase in demand as the global population grows. However, the present protein resources may not be sufficient to accommodate future consumption levels, and approximately 1 billion people already experience insufficient dietary protein intake [2]. Although animal-based proteins are considered a high-quality source of essential amino acids, concerns over the inefficiency of livestock processes, ethical issues, and environmental impacts make them unsustainable sources [2; 3]. These constraints have prompted the exploration of sustainable and eco-friendly alternatives, particularly protein-rich food sources [4; 5].  
Recently, microalgae have emerged as sustainable non-animal foods as well as protein supplements [6]. They not only play a role in mitigating global warming by acting as natural carbon sinks, but also have the potential to reduce pressure on arable land and freshwater resources required for terrestrial food production [7; 8]. _Arthospira_, a representative cyanobacterium also known as _Spirulina_, is widely consumed as a food supplement and boasts a high protein content, has well-balanced essential amino acids, is low in fat, and possesses essential fatty acids, a high vitamin content, chlorophyll, and phycobilproteins [9; 10; 11]. In addition to _Arthospira_, numerous species of microalgae and cyanobacteria have been evaluated as food supplements [10].  
In 2015, an unknown filamentous cyanobacterium was discovered in _Arthospira_ ponds and was subsequently named _Leptolynghya_ sp. KIOST-1 [12]. This strain demonstrated biomass productivity, a high protein content, and an amino acid composition comparable to _A. maxima_, with no observed cytotoxicity [12]. Moreover, subsequent research identified no putative cyanotoxin genes, and the dried biomass did not exhibit acute toxicity in experimental animals [13; 14]. These results suggest that _Leptolynghya_ sp. KIOST-1 may have potential as a food supplement. Previous studies have confirmed the optimal cultivation temperature (30 \({}^{\circ}\)C) for this strain and conducted a growth comparison between _Leptolynghya_ sp. KIOST-1 and _A. maxima_ cultured in Society of Toxicology (SOT) medium on a laboratory scale [12]. However, this research is insufficient to assess the viability of this strain for industrial production. In the industrial cultivation of microalgae, the key lies in identifying and controlling the cultivation environment to promote the efficient growth of the target species [15]. Furthermore, despite being a cyanobacterium, no analysis of the active photosynthetic pigments (chlorophyll and phycobilproteins) has been performed. Therefore, this study aimed to identify an optimal culture medium for scaling up cultivation to an industrial scale and analyze its proximate and phytochemical compositions. Additionally, we sought to elucidate growth characteristics in response to variations in carbon, nitrogen, salinity, and pH in the optimal culture medium. The findings of this study contribute to the evaluation of the industrial production potential of _Leptolynghya_ sp. KIOST-1 and provide fundamental and advantageous information for the industrial-scale cultivation thereof.