Storage Granule Variety
Some types of storage granules, like poly-phosphate and poly-hydroxybutyrate, are very densely packed and clearly delineated from the rest of the cytoplasm. Others are less tightly packed and more amorphous, like the ones in this Agrobacterium tumefaciens cell. We do not yet know what these contain.
In some species, like the Cupriavidus necator on the last page, storage granules seem to be positioned randomly in the cell. Other species have more regulated arrangements. A. tumefaciens cells always have one poly-phosphate storage granule, located near a cell pole. Other species have one at each end of the cell. As we will discuss in Chapter 5, this arrangement can help mother cells deliver a storage granule to each of their daughters during division.
You might expect a close relationship between cellular factories and storage depots. In fact, there does seem to be a relationship between carboxysomes and storage granules, although the details remain unclear (⇩).