Intracellular Structures of Prokaryotes: Inclusions, Compartments and Assemblages

Discrete structures found within the cytoplasm of the prokaryotic cell (in one case in the periplasm) represent certain aspects of an organism's metabolic capability. The structures, varying in size, shape, content, and architecture, are either naked or surrounded with a barrier, for example, a protein shell or coat, a lipid monolayer, a protein-lipid monolayer, or a lipid-protein bilayer (unit membrane). A brief, up-to-date overview is provided for each of 14 structural types: anammoxosomes, carboxysomes, chlorosomes, gas vesicles, insecticidal proteins, magnetosomes, phycobilisomes, proteasomes, and granules of cyanophycin, glycogen, polyhydroxyalkanoates (PHA), polyphosphate, triacylglycerols (TAG) and wax esters (WE). Each of the structures, based on their primary function, is placed into one of three categories: (1) structures as metabolic machinery, (2) structures as contributors to cell mobility, and (3) structures as metabolic reserves.