The unconventional adverse effects of fungal pretreatment on iturin A fermentation by Bacillus amyloliquefaciens CX‐20

Abstract

Fungal pretreatment is the most common strategy for improving the conversion of rapeseed meal (RSM) into value-added microbial products. It was demonstrated that Bacillus amyloliquefaciens CX-20 could directly use RSM as the sole source of all nutrients except the carbon source for iturin A fermentation with high productivity. However, whether fungal pretreatment has an impact on iturin A production is still unknown. In this study, the effects of fungal pretreatment and direct bio-utilization of RSM for iturin A fermentation were comparatively analysed through screening suitable fungal species, and evaluating the relationships between iturin A production and the composition of solid fermented RSM and liquid hydrolysates. Three main unconventional adverse effects were identified. (1) Solid-state fermentation by fungi resulted in a decrease of the total nitrogen for B. amyloliquefaciens CX-20 growth and metabolism, which caused nitrogen waste from RSM. (2) The released free ammonium nitrogen in liquid hydrolysates by fungal pretreatment led to the reduction of iturin A. (3) The insoluble precipitates of hydrolysates, which were mostly ignored and wasted in previous studies, were found to have beneficial effects on producing iturin A. In conclusion, our study verifies the unconventional adverse effects of fungal pretreatment on iturin A production by B. amyloliquefaciens CX-20 compared with direct bioutilization of RSM.

A Two-step Strategy for High-Value-Added Utilization of Rapeseed Meal by Concurrent Improvement of Phenolic Extraction and Protein Conversion for Microbial Iturin A Production

“…Trametes sp. 48,424 was obtained from the School of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China ( Chen et al, 2021 ). The strains were maintained in the form of spores, in dry sand at 4°C.…”

“…Pretreatment with A. oryzae 92,011 and Trametes sp. 48,424 increased the proteins content in 92011F and 48424F by about 13% as compared to untreated RSM (from 39.48 to 45.51% and 44.54%, respectively), mainly due to the decreased carbohydrate content after fermentation (Chen et al, 2021). The extraction residues derived from untreated RSM, 92011F and 48424F were designated as RSMeR, 92011eR and 48424eR.…”

“…We also previously showed that fungal pretreatment of RSM had an unconventional inhibitory effects on iturin A production by B. amyloliquefaciens CX-20 compared with direct bio-utilization of RSM as the nitrogen source. We argued that this inhibitory effect was due to the presence of compounds such as phenolics with antibacterial effect released by fungal pretreatment ( Chen et al, 2021 ). Therefore, removing as much as possible these antibacterial compounds from RSM should improve its exploitation as valuable protein feedstock substrate for production of iturin A by microbial fermentation.…”

“…Aspergillus oryzae 92,011 and Trametes sp. 48,424 were selected for fungal source to carry out these pretreatments, due to their ability to produce various glycosylhydrolase enzymes that degrade plant cell wall ( Chen et al, 2021 ). Following this first step, we examined whether ethanol under acidic condition could be an efficient extraction condition to extract as much as antioxidant phenolic compounds from RSM while minimize protein loss.…”

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“…Although the single fungal pretreatment procedure was beneficial to increase the protein content and to release antioxidant phenolic compounds from RSM likely by degrading or breaking complex matrix compounds such as polysaccharides and lignin (Shi et al, 2015(Shi et al, , 2016Bhanja Dey et al, 2016;Salakkam et al, 2017;Salakkam and Webb, 2018;Zhu et al, 2018;Wang et al, 2020;Chen et al, 2021), the antibacterial property of the obtained treated RSM was still important. At the same time, the single ethanolic extraction procedure has been shown to be effective in removing most of the antibacterial and antioxidant components from RSM, but its drawback was to reduce the protein content present in the final residue.…”