Bacillus atrophaeus Outer Spore Coat Assembly and Ultrastructure

Our previous atomic force microscopy (AFM) studies successfully visualized native Bacillus atrophaeus spore coat ultrastructure and surface morphology. We have shown that the outer spore coat surface is formed by a crystalline array of approximately 11 nm thick rodlets, having a periodicity of approximately 8 nm. We present here further AFM ultrastructural investigations of air-dried and fully hydrated spore surface architecture. In the rodlet layer planar and point defects as well as domain boundaries similar to those described for inorganic and macromolecular crystals were identified. For several Bacillus species rodlet structure assembly and architectural variation appear to be a consequence of species-specific nucleation and crystallization mechanisms that regulate the formation of the outer spore coat. We propose a unifying mechanism for nucleation and self-assembly of this crystalline layer on the outer spore coat surface.