Diversity in sporulation and spore properties of foodborne Bacillus strains
The findings presented in the study of Antonina Krawczyk have important implications for practices in the food industry as they argue against standardization of risk assessment and preservation techniques and provide means for the detection of problematic spore-formers.
Bacterial sporulation is a last resort adaptive strategy against starvation, resulting in the formation of dormant and extremely resistant (endo)spores. Spores pose major problems for the food industry, as food processing treatments often fail to completely inactivate these contaminating agents. Consequently, revival of the vegetative growth by surviving spores via germination and outgrowth can lead to food spoilage. Significant heterogeneity on a single-cell/spore level and inter-strain variation is spore properties hinder prediction and control over spores in the food industry. In this thesis, we described an extent of these two phenomena in model laboratory strains and industrially relevant, foodborne Bacillus isolates. First, using time-lapse fluorescent microscopy, we showed the occurrence of “the sporulation lysis” phenotype in sporulating genetically-identical cells of B. subtilis, demonstrating another aspect of the sporulation-related heterogeneity. Secondly, the RNA-Seq analysis revealed conservation of sporulation gene expression programs in B. subtilis and B. amyloliquefaciens strains, suggesting that distinct phenotypic traits of their spores result rather from differences in the gene presence and sequences than from the strains’ transcriptional behavior. Finally, associating germination phenotypes with the genomic content of B. subtilis and B. thermoamylovorans strains allowed for the identification of genetic factors responsible for the inter-strain variation in germination, such as the spoVA2mob operon or sequences of ger genes. Overall, the findings presented in this study have important implications for practices in the food industry as they argue against standardization of risk assessment and preservation techniques and provide means for the detection of problematic spore-formers.