Manipulating differentiation of Bacillus spp. to minimize spoilage of dairy products
Bacillus spp. form inert resting states, called endospores, which are extremely resistant to a wide range of environmental insults including radiation, high temperature and chemicals. The biochemical processes leading to the spore state involve the co-ordinated regulation of hundreds of genes, and sporulation in Bacillus subtilis has become a model system for study of processes of cellular differentiation. More recently the phenotypic plasticity of Bacillus spp. has been shown to extend to numerous distinct cell types in genetically identical populations. Some of these differentiated states, e.g. cells that are motile, that have sporulated, that produce degradative enzymes, or secrete toxins that allow them to cannibalize their neighbours, are mutually exclusive.
Recent research has unraveled much about the (sigma) factors, genea, kinases etc. involved in regulation of Bacillus spp. into these differentiated states, but much remains to be learned about the specific triggers of the hypersensitive gene expression systems that lead to 'bistability' in phenotype among genetically identical populations.
Bacillus spp. also cause spoilage of a range of high-value, heat processed, dairy products. Were it possible to induce such cells into differentiated states other than spores, they would be more easily eliminated by standard thermal processes (e.g. pasteurization). Conversely, if spores could be discouraged from germinating, or if vegetative cells could be induced to be motile rather than excrete degradative enzymes, their potential to cause spoilage would be greatly reduced.
The proposed PhD project will be linked to a recently-awarded collaborative project involving the Food Safety Centre, Dairy Innovation Australia Limited, CSIRO (Division of Food and Nutritional Sciences) and University of Queensland, in which we will identify Bacillus species of relevance to processed dairy products and characterize their ecology in the natural and food and food processing environments. The PhD project specifically will study physiological triggers of sporulation, exoprotease/exopolysaccharase production, and motility to explore whether these differentiated states can be reliably induced as a means to limit the effects of Bacillus spp. responsible for spoilage in processed dairy products. The project will build on proteomic and genomic capacity and expertise being built within the group.
Supervisors: Assoc Professors Tom Ross, John Bowman and Professor Mark Tamplin
|Contact:||Assoc Prof Tom Ross |