Improved Production of Spores and Bioactive Metabolites from Bacillus amyloliquefaciens in Solid-state Fermentation by a Rapid Optimization Process

A dipicolonic acid fluorimetry assay was used instead of plate counting for the assessment of spore yields for enhanced optimization efficiency. The associated parameters, including the ratio of solid substrates, composition of liquid substrates, and cultivation conditions, were systematically optimized in a shake-flask culture. The maximum spore yield of 7.24 × 1010 CFU/g of wet substrate was achieved. The optimization process produced a 25.7-fold increase in spore yields compared with those before optimization. In addition, the maximum release of bioactive metabolites during spore accumulation was subsequently obtained with 573.0 U/g of protease, 188.8 U/g of amylase, 186.8 U/g of cellulase, and 3.45 mg/g of acid-soluble protein. The experiment provides a methodological basis for the rapidly optimized production of Bacillus spores in pure solid-state fermentation.