High yield of heat-resistant spores of Bacillus megaterium in bioreactors

Microbial inoculants have been proposed as a sustainable and cost-effective alternative to conventional agricultural practices. However, the effectiveness of these bio-based products can be negatively impacted by reduced cell viability during product development, storage, and commercialization. To address these limitations, it is critical to identify and optimize the cultivation conditions that can lead to the production of highly resistant spores for use as inoculants. In this study, optimal cultivation conditions for obtaining Bacillus megaterium B119 spores in bioreactors were reached, with increases in the sporulation efficiency and heat resistance. The best nutrient medium and optimal temperature and initial pH conditions were obtained on shake flask experiments and subsequently validated in two bench-scale bioreactor models (stirred and aerated tank and the bubble column). The optimized temperature and initial pH were found to be 37 °C and 5.6. The highest concentration of heat-resistant Bacillus spores of 1.31·1012 CFU/mL was obtained in the bubble column bioreactor with a sporulation efficiency of 100.0%, a heat resistance of 78.4%, and an energetic efficiency on spores production of 4.83·1010 CFU/J. The production of highly resistant spores can significantly improve the survival rate of microorganisms during inoculant production and application, thereby enhancing their effectiveness in the field.