DISRUPTION OF A GLYCOGEN-BRANCHING ENZYME GENE, GLGB, SPECIFICALLY AFFECTS THE SPORULATION-ASSOCIATED PHASE OF GLYCOGEN ACCUMULATION IN STREPTOMYCES-AUREOFACIENS

In the course of Streptomyces differentiation, glycogen is accumulated in two discrete phases: in substrate hyphae that undergo aerial mycel ium formation (phase I), and during septation of aerial hyphae (phase II). We have disrupted a previously identified gene, glgB, encoding a putative glycogen-branching enzyme in Streptomyces aureofaciens. Disru ption of the gene had no profound effect on sporulation. However, the amount of glycogen-like polysaccharides, compared to wild-type (WT) S. aureofaciens, decreased in the late stage of differentiation of the g lgB-disrupted strain. Absorption spectra of polysaccharides extracted from the Wi and glgB-disrupted strains have shown the presence of glyc ogen in both strains in the first stage of differentiation (aerial myc elium formation), and unbranched glucan was detected in the glgB-disru pted strain in the late stage of differentiation. The results were con firmed by electron microscopy after silver proteinate staining of glyc ogen granules. Two distinct glycogen-branching enzymes, which had temp orally different expression during differentiation, were detected in W T S. aureofaciens. The absence of this enzyme activity in the late sta ge of differentiation in the glgB mutant suggests that the product of the glgB gene is responsible for phase II glycogen accumulation.