Molecular Soil Biology 2026, Vol.17, No.1, 1-11 http://bioscipublisher.com/index.php/msb 5 Figure 4 Changes in cell viability of microalga SA-2 under different treatments Note: (a) EDTA-Ca at different concentrations; (b) EDTA-Fe at different concentrations. Different lowercase letters indicate a significant difference (P<0.05) 2.4 Effects of EDTA-Fe and EDTA-Ca treatments on microalgal protein content Changes in microalgal protein content on day 12 were measured under different concentrations of EDTA-Ca and EDTA-Fe. The results showed that protein content was highest at an EDTA-Ca concentration of 0.3 mg/L, reaching 0.1 mg/mL (Figure 5a). For EDTA-Fe, the maximum protein synthesis occurred at 0.2 mg/L, with a protein content of 0.14 mg/mL (Figure 5b). These findings indicate that EDTA-Ca at concentrations below 0.3 mg/L and EDTA-Fe at concentrations below 0.2 mg/L promoted protein synthesis in SA-2. Conversely, EDTA-Ca concentrations above 0.3 mg/L and EDTA-Fe concentrations above 0.2 mg/L inhibited protein synthesis. The promotive effect of low-concentration EDTA-Fe (<0.2 mg/L) on protein synthesis was more pronounced than that of low-concentration EDTA-Ca (<0.3 mg/L), whereas the inhibitory effect of high-concentration EDTA-Fe (>0.2 mg/L) was stronger than that of high-concentration EDTA-Ca (>0.3 mg/L). Figure 5 Changes in protein content of microalgae SA-2 Note: (a) treatment groups with different concentrations of EDTA-Ca; (b) treatment groups with different concentrations of EDTA-Fe. Different lowercase letters indicate a significant difference (P<0.05) 2.5 Effects of EDTA-Fe and EDTA-Ca treatments on microalgal lipid content The changes in microalgal lipid content under different concentrations of EDTA-Ca and EDTA-Fe were measured. Lipid content reached its maximum under 0.3 mg/L EDTA-Ca treatment, with a value of 11.83 mg/L (Figure 6b). For EDTA-Fe, the highest lipid content was observed at 0.2 mg/L, reaching 13.45 mg/L (Figure 6c). These results indicate that EDTA-Ca at concentrations below 0.3 mg/L and EDTA-Fe at concentrations below 0.2 mg/L promoted lipid synthesis in SA-2. Conversely, EDTA-Ca concentrations above 0.3 mg/L and EDTA-Fe concentrations above 0.2 mg/L inhibited lipid synthesis. The promotive effect of low-concentration EDTA-Fe (<0.2 mg/L) on lipid accumulation was more pronounced than that of low-concentration EDTA-Ca (<0.3 mg/L), while the inhibitory effect of high-concentration EDTA-Fe (>0.2 mg/L) was stronger than that of high-concentration EDTA-Ca (>0.3 mg/L).
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