Application of online spectroscopic techniques for detection of Bacillus spores in cultivations with complex medium

Bacillus spores are important in a range of biotechnological applications. Real-time spore detection methods are advantageous for effectively characterizing and optimizing the spore production processes. In this study, a qualitative high-throughput method for online monitoring of Bacillus spore formation using spectroscopic techniques is presented. An increase in specific fluorescence at an excitation wavelength of 390 nm and an emission wavelength of 460 nm was observed during the cultivation of the spore-forming Bacillus subtilis PY79 strain in a BioLector device, which correlated with the release of spores from the mother cells in a complex medium. Therefore, spore release can be monitored in high-throughput experiments by real-time measurement of this fluorescence wavelength combination. Additionally, the applicability of this method to Bacillus strains other than B. subtilis highlights its broad relevance in industrial processes. This method has the potential to detect spores more reliably and efficiently than conventional methods such as plating techniques. Finally, quenching experiments with iron ions indicated that a siderophore causes the characteristic fluorescence signal, demonstrating the usefulness of this method also in research areas focused on siderophores.