Bacterial and Archaeal Inclusions

Bacterial inclusions can be defined as discrete structures seen within the confines of prokaryotic cells, generally intracytoplasmic, but in some instances in the periplasmic region of the cell. Inclusions function as metabolic reserves, cell positioners, or as metabolic organelles. Some inclusions may contribute to more than one of these functions. Those that function as metabolic reserves are glycogen, polyhydroxyalkanoate, wax ester, triacylglycerol, cyanophycin, and polyphosphate granules, and sulfur globules. These reserves are commonly accumulated in response to a nutrient imbalance, for example, under conditions of excess carbon/energy. Magnetosomes and gas vesicles contribute to cell mobility thereby assisting the cells in attaining nutrient and/or redox needs. Carboxysomes, containing the enzyme ribulose bisphosphate carboxylase/oxygenase, and chlorosomes, sacs of self-aggregated bacterriochlorophyll are carbon-fixing and light-harvesting organelles, respectively. Key Concepts: The cytoplasmic region of prokaryotic cells can be much more complex than originally thought. In addition to flagella, many prokaryotes have developed mechanisms whereby they are capable of positioning/orienting themselves in an aqueous environment. Although not as complex as the well-known eukaryotic organelles, many prokaryotes possess simple organelles. Many of the inclusions may have useful properties for applications in biotechnology Keywords: granules; globules; vesicles; crystals; metabolic reserves; simple organelles; inclusions; mobility