The interplay of glycogen metabolism and differentiation provides an insight into the developmental biology of Streptomyces coelicolor

Mycelial colonies of the developmentally complex actinomycete Streptomyces coelicolor growing on solid medium contain glycogen in two distinct locations. Phase I deposits are found in a substrate mycelium region bordering the developing aerial mycelium. Their production involves GlgBl, one of two glycogen branching enzyme isoforms. Phase 11 deposits occur in the upper regions of aerial hyphae, in long tip cells that are dividing, or have just divided, into unigenomic prespore compartments. Their formation involves a second branching enzyme isoform, GlgBll. To find out if the gene for the second isoform, glgBll, is regulated by any of the well-studied whiA, B, G, H or l genes needed for sporulation septation, glJBl or glgBll was disrupted in a set of whi mutants, and the glycogen phenotypes examined by transmission electron microscopy. In the whiG mutants, deposits were found throughout the aerial mycelium and the adjacent region of the substrate mycelium, but the morphology of all the deposits, i.e. whether they were in the form of granules of branched glycogen or large blobs of unbranched glycan, depended solely on GlgBl. In contrast, the whiA, B, H and / mutations had no obvious effect on the pattern of glycogen deposition, or on the spatial specificity of the branching enzyme isoforms (though phase 11 glycogen deposits were reduced in size and abundance in the whiA and B mutants, and increased in the whiH mutant). These results indicate that glgBll is regulated (directly or indirectly) by whiG, and not by any of the other whi genes tested, and that the aerial hyphae of a whiG mutant are atypical in being physiologically similar to the substrate hyphae from which they emerge. A new role for aerial hyphae is proposed.