Sporulation kinetics of Bacillus subtilis under dynamic temperature conditions: impact on gene expression and spore properties.

Bacillus subtilis forms highly resistant spores that contribute to food spoilage but are also valuable for biotechnological applications. While temperature strongly affects sporulation and spore properties, industrial temperature profiles are often dynamic and remain poorly accounted for in predictive models. In this study, growth and sporulation were monitored under four temperature scenarios. A static 37.0 °C condition was compared with three dynamic profiles: after 16 h at 37.0 °C, cultures were cooled to 10.0 °C, cooled to 10.0 °C for 24 h, then returned to 37.0 °C, or cooled to 20.0 °C. Growth and sporulation were modelled using an adapted version of Gauvry etal. model. RT-qPCR was used to assess transcriptional responses associated with sporulation, stress adaptation, and spore properties. The heat resistance and germination of the resulting spores were also investigated. Cooling to 10.0 °C blocked sporulation and sporulation gene expression, both of which resumed after re-incubation at 37.0 °C. Cooling to 20.0 °C did not stop the process but delayed it. Gene expression was heterogeneous, suggesting that some cells had already initiated sporulation before cooling. Spores formed under this condition showed significantly lower heat resistance and higher germination efficiency in L-alanine than spores formed at 37.0 °C, probably reflecting changes during spore assembly. These results show that dynamic temperature conditions alter both sporulation kinetics and spore properties. The adapted model incorporates temperature kinetics and can therefore predict sporulation under dynamic temperature profiles, improving microbial risk assessment and supporting the optimisation of beneficial spore production for biotechnological applications.