Morphology of poly-β-hydroxybutyrate granules

Electron microscopy and methods of polymer physics were used to investigate the texture of bacterial storage granules, namely, poly-β-hydroxybutyrate. The first level of native granule morphology is 100 to 150 Å fibrils, involving extended polymeric chains. Fibrils are believed to represent a unique morphology which develops because of the simultaneous synthesis and crystallization which occurs during some stage of formation. It is assumed that fibrillar aggregates are important in the internal organization of the granule, based on differences both in response to temperature and in small-angle scattering of native poly-β-hydroxybutyrate granules compared to single-crystal poly-β-hydroxybutyrate. The fibrils can re-organize into 50 Å thick ribbons when in aqueous acetone, and are further transformed into single-crystal lamellae with folded chains. Polymer synthesis and crystallization are discussed and a model is presented to explain how these events might occur on the surface of the polymerizing enzyme.