TISSUE-SPECIFIC GLYCOGEN BRANCHING ISOENZYMES IN A MULTICELLULAR PROKARYOTE, STREPTOMYCES-COELICOLOR A3(2)

In the overtly differentiated colonies of Streptomyces coelicolor A3(2), discrete phases of glycogen synthesis are found at the vegetative/aerial mycelium boundary (phase I) and in the immature spore chains at aerial hyphal tips (phase II). We have characterized two S. coelicolor glgB genes encoding glycogen branching enzyme, which are well separated in the genome. Disruption of glgBI led to the formation of abnormal poly-glucan deposits at phase I, with phase II remaining normal, whereas disruption of glgBII interfered specifically with phase II deposits, and not with those of phase I. Thus, each branching enzyme isoform is involved in a different phase of glycogen synthesis. This situation contrasts with that in simple bacteria, which typically have a single set of enzymes for glycogen metabolism, and more closely resembles that in plants.