Ultrastructure of exospore formation in Streptomyces revealed by cryo-electron tomography

Many bacteria form spores in response to adverse environmental conditions. Several sporulation pathways have evolved independently and occur through distinctive mechanisms. Here, using cryo-electron tomography (cryo-ET), we examine all stages of growth and exospore formation in the model organism Streptomyces albus. Our data reveal the native ultrastructure of vegetative hyphae, including the polarisome and filaments of ParA or FilP. In addition, we observed septal junctions in vegetative septa, likely involved in effector translocation between neighbouring cells. During sporulation, the cell envelope undergoes dramatic remodeling, including the formation of a spore cortex and two protective proteinaceous layers. Mature spores reveal the presence of a continuous spore coat and an irregular rodlet sheet. Together, these results provide an unprecedented examination of the ultrastructure in Streptomyces and further our understanding of the structural complexity of exospore formation.Competing Interest StatementThe authors have declared no competing interest.View Full Text