PhD study trip
Spore sublethal damage repair mechanisms
Spores are ubiquitously present in the environment and can lead to food spoilage and food-borne illnesses.
The spores’ high resistance to food processing treatments is a major challenge for the food industry. Currently applied treatments are sufficient to kill spores. However, food industry is looking for milder preservation and processing strategies, which would provide better products with higher sensory quality and nutritious values without diminishing safety level. Attempts are mainly directed towards the use of milder heat treatments and combinations of treatments. However, reducing the treatment intensity may lead to a fraction of spores that are damaged rather than inactivated (1) and that may resume germination after the damage has been repaired.
Aim
In our project we are interested in whether mild preservation treatments lead to spore damage and whether this damage can be repaired so that the spores can continue germination and outgrowth process.
Research
The objective of our research is to gain insight in the amount of damage and repair that occur during sublethal (heat) treatment of spores derived from Bacillus subtilis and Bacillus cereus, a food-borne pathogen. Heat treatment and recovery conditions have been established. Selective plating and monitoring OD changes during germination and outgrowth (2) showed a high fraction of damaged spores and delayed germination/outgrowth at the population level. Our methodology includes investigation and comparison of two conditions, an untreated one and treated one, by comparative transcriptome analysis, followed by construction of targeted deletion mutants for differently expressed genes. Phenotypic analysis of mutants will allow for identification of the role of candidate genes in repair mechanisms, and lead to identification of the biomarkers for spore damage repair. Studying outgrowth behaviour at single spore level is possible with flow-cytometry, a powerful tool allowing for assessment of germination and outgrowth stages and simultaneous spore sorting (3), allowing for e.g. comparison of (heat) treated single germinated spores in various recovery conditions.
Conclusion
Gaining knowledge on spore damage and repair, identification of the mechanisms involved in repair of sublethally damaged spores, and finally selection of biomarkers for prediction of the capacity of spores to repair the damage and to grow out can allow for improved food safety and quality particularly in case of minimally processed foods and ambient stable foods.