Autoregulatory factors of secondary metabolism and morphogenesis in actinomycetes

The Gram-positive bacterial genus Streptomyces possesses interesting biological aspects, such as the ability to produce a wide variety of secondary metabolites and a mycelial form of growth that culminates in sporulation. A close relationship of secondary metabolism and cell differentiation has been well recognized; secondary metabolism might be a physiological expression of cell differentiation. A variety of diffusible low-molecular-weight chemical substances have been found to function in general as regulatory factors, like "hormones" in eukaryotes, for secondary metabolism and cell differentiation. Among these factors, A-factor has been most extensively studied. This review summarizes recent research on the chemical structures, functions, biosyntheses, and mode of action of these regulatory factors.