The protein shells of bacterial microcompartment organelles. Bacterial microcompartments: their properties and paradoxes. Microcompartments and protein machines in prokaryotes. Growing evidence suggests that the presence of organelles is the rule, rather than the exception, in bacterial cells. These complex subcellular compartments provide evolutionary advantages as well as enabling metabolic specialization, biogeochemical processes and biotechnological advances. Bacteria have fundamental mechanisms of organelle formation, through which conserved processes can form distinct organelles in different species depending on the proteins recruited to the luminal space and the boundary of the organelle. This Review highlights that, despite the diversity of reported organelles, some unifying concepts underlie their formation, structure and function. These diverse organelles have various metabolic and physiological functions, facilitating adaptation to different environments and driving the evolution of cellular complexity. Some are bound by a lipid bilayer (such as thylakoids, magnetosomes and anammoxosomes), whereas others are defined by a lipid monolayer (such as lipid bodies), a proteinaceous coat (such as carboxysomes) or have a phase-defined boundary (such as nucleolus-like compartments). Advances in imaging technologies have revealed that many bacteria possess organelles with a proteomically defined lumen and a macromolecular boundary.

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