Production of Free Amino Acid and Short Peptide Fertilizer from Rapeseed Meal Fermentation Using Bacillus flexus NJNPD41 for Promoting Plant Growth

Free amino acids and short peptides (FAPS) that play an important role in plant nutrition can be extracted from rapeseed meal (RSM) by microbial enzymolysis. The enzymolytic activity of one bacterial strain isolated from RSM for the production of FAPS fertilizer (FAPSF) via solid-state fermentation, as well as its detoxification activity for isothiocyanates and oxazolidinethione, was investigated in this study. The strain NJNPD41 isolated from RSM piled-soil possessed effective proteolytic activity and was identified as Bacillus flexus on the basis of its morphological, physiological, and biochemical properties, as well as 16S rDNA analysis. Compared to the uninoculated control, inoculation with the strain NJNPD41 significantly increased the yield of total free amino acids and short peptides by 115% and decreased the content of isothiocyanates and oxazolidinethione by 53% and 60%, respectively, after solid-state fermentation. The pot and field experiments showed that FAPSF significantly promoted eggplant growth and enhanced the fruit yield and quality of eggplant compared to the control. In conclusion, this study provided a novel method for the high-value utilization of RSM to produce high-quality and low-toxicity FAPSF using the newly isolated strain B. flexus NJNPD41.