Multicellular Development in Streptomyces

The colony structure and life cycle of the grampositive, soil‐dwelling bacterium Streptomyces coelicolor provide a fascinating exception to the view of bacteria as simple unicellular microorganisms. Mutations in genes involved in morphogenesis alter colony appearance but do not usually compromise viability. The majority of genes identified as being important for aerial hypha formation encode regulatory proteins; however, recent work has resulted in the characterization of two classes of structural molecules that are necessary for aerial development: the SapB surfactant peptide (specified by the ram gene cluster) and eight chaplin proteins (ChpA through H). It has been found that while Streptomyces has many of the conventional genes that are necessary for these processes to occur, Streptomyces cells are organized very differently from other bacteria and these differences are highly relevant to colony development and spore formation. In Streptomyces, however, DivIVA is an essential protein that does not seem to be associated with cell division but rather is crucial for coordinating cell wall growth. The basic mechanism of Z‐ring formation appears to be shared between S. coelicolor and other prokaryotes; however, there are important differences in how Streptomyces employs and executes cell division. Streptomyces has no homologues of the Bacillus subtilis or Escherichia coli MinC or MinD proteins and uses its DivIVA for functions apparently unrelated to cell division.