Bacillus subtilis is a well-studied model organism that is able to form dormant endospores. These spores can survive harsh environmental conditions and therefore are a major concern to the food industry.
In this research the focus lies on food isolates of B. subtilis that produce spores with very high heat resistance. Heat treatment is commonly applied in the food industry to reduce the bacterial content in products resulting in the prevention of spoilage and a longer product shelf life. Clearly, there is large variation between heat resistances of spores between different strains, and it has also been established that sporulation conditions are important in determining the final heat resistance properties of spores [1,2].
This project aims at identifying the molecular mechanisms underlying spore heat resistance. After establishing the differences in spore heat resistance between strains, phenotypic and genotypic characterization of extreme heat resistant strains will be performed.
In this study we characterized 15 aerobic mesophilic spore formers belonging to the species Bacillus subtilis which were isolated from food products. The thermal inactivation kinetics of the different strains were determined by batch inactivation using capillary tubes and for a selection of 5 strains the inactivation kinetics were determined in a continuous flow microheater, thereby mimicking UHT treatment. Based on the inactivation kinetics strains were selected for whole genome sequencing to identify genetic differences that might be at the basis of increased spore heat resistance.
To identify genetic differences that are at the basis of increased spore heat resistance the genome sequences of 15 strains were analyzed against the background of their spore heat resistances. Further investigation will be required to validate the influence of the identified genetic markers on the spore heat resistance properties.
The heat resistance of spores varies greatly amongst different strains of B. subtilis that were isolated from different sources. The data generated in this study can be used for an improved control of bacterial spores in food.
1. Brul, S., van Beilen, J., Caspers, M., O'Brien, A., de Koster, C., Oomes, S., Smelt, J., Kort, R., and Ter Beek, A. (2011). Challenges and advances in systems biology analysis of Bacillus spore physiology; molecular differences between an extreme heat resistant spore forming Bacillus subtilis food isolate and a laboratory strain. Food Microbiology 28, 221-227.
2. Lima, L.J.R., Kamphuis, H.J., Nout, M.J.R., and Zwietering, M.H. (2011). Microbiota of cocoa powder with particular reference to aerobic thermoresistant spore-formers. Food Microbiology 28, 573-582.