Establishment of a rapeseed meal fermentation model for iturin A production by Bacillus amyloliquefaciens CX-20.

Iturin A is an important broad-spectrum antifungal cyclic lipopeptide used as an ideal potential biological control agent. However, its application is limited mainly due to the producer strains' low productivity and the high production costs. Here, a potentially industrial strain Bacillus amyloliquefaciens CX-20 was proved to use low-cost rapeseed meal (RSM) as the sole source of all nutrients except the carbon source for the high productivity of iturin A. A fermentation model was first established to analyse the specific roles of different RSM components on iturin A production. Proteins and minerals in RSM were confirmed to play positive role, whereas fibre had negative effect. And the maximal concentration of iturin A was predicted to be more than 1.64 g l by the established evaluation model. Moreover, submerged fermentation of B. amyloliquefaciens CX-20 demonstrated a strong ability to hydrolyse RSM and release water-soluble nutrients. This fermentation broth, a mixture of Bacillus, iturin A and RSM hydrolysate, could simultaneously combat clubroot disease and promote the growth of Brassica napus. In conclusion, this study provides a promising strategy to achieve full utilization of RSM for the production of a combination of value-added biological control agent and biofertilizer.