HETEROGENEITY IN SPORULATION-SPECIFIC GENE EXPRESSION REFLECTING DIFFERENT GERMINATION RESPONSES OF BACILLI SPORES
Some gram-positive genera of bacteria, including Bacillus, can enter the sporulation process in response to nutrient limitation. Spores are able to survive severe environmental conditions such as heat, oxidative damage, UV and gamma radiation. Although spores do not have metabolic activity and can remain dormant for years, they have the ability to monitor an environment and respond to nutrient and non-nutrient stimuli via germination and cell outgrowth. Bacillus spores are found in a wide variety of environments, including food stuffs. Both sporulation and germination are heterogeneous processes. Not all cells within one genetically identical population sporulate in response to starvation. Moreover, genetically homogeneous spores differ in resistance properties and germination behaviour. Such heterogeneity is a significant problem within the food industry since it complicates the prediction of spore/cell behaviour and impedes removal of all spores from food products by (mild) preservation techniques. Subsequent germination and outgrowth of remaining spores often leads to food spoilage, shorter shelf-life of food products and, in some cases, food-borne ilnesses. Therefore, elucidation of molecular mechanisms and environmental factors leading to heterogeneous properties of spores is a task of great importance.
In this project we study the heterogenous expression of sporulation- and germination-specific genes during sporulation of B. subtilis and B. cereus. We ultimately try to find correlations between expession profiles of specific genes and the outcome in spore properties and germination behaviour. Our approach includes investigation of transcription patterns of these genes on a single cell level with flow-cytometry and (time-lapse) fluorescence microscopy.