Optimization of iturin A production from Bacillus subtilis ZK-H2 in submerge fermentation by response surface methodology

In this research, single-factor and response surface experiments were conducted in the fed-batch fermentation process to improve the yield of iturin A. The effect of adding various concentrations of precursor amino acids l-asparagine (Asn), l-aspartic acid (Asp), l-glutamic acid (Glu), l-glutamine (Gln), l-Serine (Ser) and l-proline (Pro) at different adding times (3 and 12 h) on iturin A production and cell growth was studied. The respective addition of amino acids (Asp 0.28 g/L; Asn 0.36 g/L; Glu 0.20, 0.28 and 0.360 g/L; Gln 0.20, 0.28 and 0.36 g/L; Pro 0.12, 0.20, 0.28 and 0.36 g/L) at 3 h was shown to improve cell growth but did not affect the yield of iturin A. Meanwhile, the individual addition of the same amino acids at 12 h improved cell growth and increased the yield of iturin A. Excellent correlation was obtained between the predicted and measured values, suggesting that the regression model was accurate and reliable; highly significant (P < 0.0001), and the determination coefficient (R-2 = 0.975). When 0.0752 g/L Asn; 0.1992 g/L Gln and 0.1464 g/L Pro were added at 12 h, the yield of iturin A reached 0.85 g/L, which is 32.81%-fold higher than that of the initial process. Therefore, this study obtained optimal parameters for iturin A production by the experimental method, and process validation gave high iturin A yields (0.85 g/L) during a 60 h fermentation. These findings could guide an up-scaling of the fermentation process.