Process Regulation Of Effective Iturin A Fermentation By Bacillus Subtilis Based On Rapeseed Meal As The Nitrogen Source

Iturin A is a cyclic lipopeptide antibiotic with strong antifungal action. It is a potential weapon for controlling plant diseases caused by phytopathogenic fungi. However, a significant obstacle to large-scale industrial application of cyclic antibiotics such as iturin A is the high production cost coupled with a low production rate.To improve the iturin A fermentation and decrease its production cost, the feasibility of using untreated low cost rapeseed meal as a nitrogen source to produce valuable iturin A by Bacillus subtilis 3-10 in submerged fermentation was investigated. A series of process optimization and control strategies have been proposed to improve iturin A production based on the relationship of nutritional components, cell growth, iturin A synthesis characteristics, as well as the transmission electron microscopy analysis (TEM). The final iturin A production was improved notably compared with its initial production level. The main results of this study are as follows:(1) The influence of different nitrogen sources on iturin A production was investigated. We proved the effectiveness of low cost rapeseed meal as a nitrogen source to produce valuable iturin A. The highest iturin A concentration in batch bioreactor culture reached 0.60 g/L, which was significantly higher than that produced with peptone (0.5 g/L) and ammonium nitrate (0.067 g/L) as nitrogen sources.(2) The effect of different glucose feeding rates on iturin A production was investigated. A stepwise two-stage glucose feeding strategy was proposed based on the relationship of cellular metabolic characteristic and iturin A production with different constant feeding rates. With this novel feeding strategy, the ratio of spores to total cells could be maintained at a desirable/stable level of 0.80-0.86, the maximum iturin A concentration reached 1.12 g/L, which was about two-fold higher than that of batch culture.(3) The effect of different carbon sources on iturin A production was investigated. Wheat bran was proved to be the optimal carbon source for iturin A production. By comparing the differences of cell growth and iturin A production under glucose and wheat bran as carbon sources, a mixed carbon sources fermentation strategy of glucose and wheat bran was proposed. The highest iturin A concentration reached 2.02 g/L, which was 3.4 and 1.7 fold higher than that using single glucose and wheat bran as carbon sources.(4) Transmission electron microscopy analysis shows that the structure of rapeseed meal protein bodies after fermentation was smaller than that before fermentation. Moreover, when using wheat bran or mixed carbon sources of wheat bran and glucose, the rapeseed meal protein bodies became smaller and less than that using single glucose as a carbon source, suggesting that the rapeseed meal protein was used more thorough by Bacillus subtilis and more suitable for iturin A production when using wheat bran or mixed wheat and glucose as carbon sources.