Disruption of a glycogen-branching enzyme gene, glgB, specifically affects the sporulation-associated phase of glycogen accumulation in Streptomyces aureofaciens

Abstract

~~~In the course of Sfrepfomyces differentiation, glycogen is accumulated in two discrete phases: in substrate hyphae that undergo aerial mycelium formation (phase I), and during septation of aerial hyphae (phase 11). We have disrupted a previously identified gene, g/gB, encoding a putative glycogen-branching enzyme in Streptomyces aureofaciens. Disruption 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 glgB-disrupted strain. Absorption spectra of polysaccharides extracted from the WT and g/gB-disrupted strains have shown the presence of glycogen in both strains in the first stage of differentiation (aerial mycelium formation), and unbranched glucan was detected in the g/gBdisrupted strain in the late stage of differentiation. The results were confirmed by electron microscopy after silver proteinate staining of glycogen granules. Two distinct glycogen-branching enzymes, which had temporally different expression during differentiation, were detected in WT 5. aureofaciens. The absence of this enzyme activity in the late stage of differentiation in the g/gB mutant suggests that the product of the g/gB gene is responsible for phase II glycogen accumulation.

A glgC gene essential only for the first of two spatially distinct phases of glycogen synthesis in Streptomyces coelicolor A3(2)

“…The gene is accordingly termed glgCI. It follows that another glgC gene must be specific for phase II, echoing the situation previously described for glgB genes (8,18). However, the use of glgCI as a probe at low stringency against Southern blots of S. coelicolor genomic DNA has not revealed candidate sequences, suggesting considerable sequence divergence.…”

“…Likewise, the genes for phase I-and phase II-specific branching enzyme isoforms in various Streptomyces spp. appear in some, but not all, cases to have diverged enough to prevent their simultaneous detection with a single glgB probe (8,18). Surprisingly, glgCI is located far from either of the two known glgB genes, whereas, in all other bacteria analyzed, glgC and glgB are very closely linked, forming part of a cluster of all the major glg genes (22).…”

“…Each was shown to be involved in a separate phase of glycogen synthesis: glgBI in phase I and glgBII in phase II. Evidence that this is a more or less general situation among streptomycetes was obtained by Southern blotting and by work with Streptomyces aureofaciens (18) which showed that disruption of a glgB gene affected glycogen synthesis only in phase II. Because glgB mutants retained the ability to make and to degrade ␣-1,4-polyglucan deposits, it was not possible to assess the importance of glycogen metabolism for normal colony development with these mutants.…”

Duplicated gene clusters suggest an interplay of glycogen and trehalose metabolism during sequential stages of aerial mycelium development in Streptomyces coelicolor A3(2)

“…At least some of the genes of glycogen synthesis (i.e. glgB and glgC) are duplicated, one copy of each being speci®c for one of the phases of glycogen deposition (Bruton et al 1995;Homerova et al 1996;Martõ n et al 1997). It now appears that there are du- Fig.…”

Taking a genetic scalpel to the Streptomyces colony

“…Two glgB (branching enzyme) genes have been discovered in S. coelicolor, and phenotypic analysis of disruptants showed that each branching enzyme isoform is responsible for glycogen branching in one of the two locations (Bruton et al, 1995). This situation appears to be general among streptomycetes (Bruton et al, 1995;Homerova et al, 1996). Although only one glgC ( ADPglucose pyrophosphorylase) gene has been identified in S. coelicolor, the phenotype of glgC disruptants showed that this gene is responsible only for phase I glycogen synthesis, and that a second glgC gene must also exist (Martin et al, 1997).…”