Distinct cell division features in Anabaena, a multicellular cyanobacterium

Filamentous cyanobacteria such as Anabaena display a distinct multicellular organization in the bacterial kingdom. In the filament, the cells share a common periplasm and continuous peptidoglycan sacculus and outer membrane. This structure is propagated by cell division proteins with specific features, including the Z-ring components FtsZ, ZipN, and SepF. Septal junction protein complexes, which provide cell-cell cohesion and communication functions key to the Anabaena multicellular behavior, are recruited to the intercellular septa by interaction with ZipN and SepF during cell division. Anabaena also shows specific features in relation to peptidoglycan growth. The activities of the elongasome and the divisome complexes are interdependent, and septal growth is maintained throughout the cell cycle, contributing to the determination of the proper filament geometry and building and maintaining intercellular communication structures. During the differentiation of heterocysts, cells specialized for the fixation of atmospheric nitrogen, cell division is lost, setting the point of commitment to differentiation. Genes encoding Z-ring components are repressed, and the incorporation of these components into functional divisional complexes is inhibited, involving specific regulatory proteins in connection to specificities of the Anabaena Z-ring. The essential dependence of FtsZ polymerization on SepF provides a mechanism for Z-ring inhibition by downregulating SepF during differentiation.