## 4 Discussion  
Previous studies have reported that _Leptolyngbya_ sp. KIOST-1 has a high protein content and no cytotoxicity, cyanotoxin-related genes, or acute toxicity, suggesting that it may be a potential protein source candidate [12; 13; 14]. In this study, we attempted to determine the fundamental physiological characteristics of this species necessary for its cultivation to produce biomass. We experimentally confirmed the growth of _Leptolyngbya_ sp. KIOST-1 in SOT medium and 3 other media (two media based on BG-11 medium and ATCC 1142 medium) among the  
Figure 6: Growth of _Leptolyngbya_ sp. KIOST-1 in modified SOT media containing 10 different concentrations of **(a)** sodium bicarbonate and **(b)** sodium nitrate as carbon and nitrogen sources, respectively (mean \(\pm\) standard error, \(n\) = 3). The control concentrations were 16.8 g L\({}^{-1}\) sodium bicarbonate and 2.5 g L\({}^{-1}\) sodium nitrate, which are similar to those of SOT medium. The y-axis shows the biomass concentration, and the x-axis shows the days of culture. Significant differences are represented using different lowercase letters. “ns” means “there is no significant difference” as determined by one-way analysis of variance (ANOVA) with post hoc Tukey’s test, where \(p\) < 0.05. The black letters on the microscopic images indicate sodium carbonate and sodium nitrate concentrations. Scale bar, 50 \(\mu\)m.  
Figure 7: Growth of _Leptolyngbya_ sp. KIOST-1 cultured in **(a)** six different salinity conditions and **(b)** five different pH conditions (mean \(\pm\) standard error, \(n\) = 3). The salinity and pH values of the control were 15 psu and pH 9.3, respectively, which are similar to those of the SOT medium. The y-axis shows the biomass concentration, and the x-axis shows the days of culture. Significant differences are represented using different lowercase letters. “ns” means “there is no significant difference” as determined by one-way analysis of variance (ANOVA) with post hoc [PERSON]’s test, where \(p\) < 0.05. 11 different culture media. Cells grown in three of the four media contained approximately 67% protein. This protein content was higher than that suggested in a previous study (51-58% dry matter) on candidate microalgae for protein production [10]. In the analysis of the photosynthetic pigments, we found that the chlorophyll-a content in _Leptolyngbya_ sp. KIOST-1 is similar to that of _Arthospira_ biomass [31; 32]. Although the content of C-phyocyanin was lower than that of _Arthospira_[32], it had a phycocyanin content similar to that of another _Leptolyngbya_ sp. which was cultured under field conditions in a previous study (20.2 \(\pm\) 0.4 mg g\({}^{-1}\)) [33]. Over the past few years, _Arthospira_ has been cultivated on a large scale as a valuable source in various industries due to its high protein content and the presence of bioactive compounds, such as C-phycocyanin and chlorophyll-a [34]. Our results suggested that _Leptolyngbya_ sp. KIOST-1 may serve as an alternative to _Arthospira_. One of the main challenges in microalgae biomass production using open raceway ponds (ORPs) is the emergence of other unintended microorganisms, known as contaminants [35]. Contamination by other microalgal species has been widely reported [36; 37]. In practice, contamination by several microalgal species disturbs the growth of cells in _Arthospira_ culture ponds [38]. In previous studies, direct contact, nutrient competition, and allelopathy, which are considered the main biological contamination problems, have been reported in microalgae cultivation [39; 40; 41]. In more severe cases, contamination causes culture failure due to cross-effects. For _Arthospira_ consumers, contamination with cyanotoxins, such as microcystine produced by other microcalga including _Microystis aeruginosa_, is a potentially harmful risk [42; 43]. There were no contaminations by other microalgal species or predators during the two industrial cultivation trials in the ORP (Figure 1).