The chitoblose-binding protein, DasA, acts as a link between chitin utilization and morphogenesis in Streptomyces coelicolor

Streptomycetes are mycelial soil bacteria that undergo a developmental programme that leads to sporulating aerial hyphae. As soil-dwelling bacteria, streptomycetes rely primarily on natural polymers such as cellulose, xylan and chitin for the colonization of their environmental niche and therefore these polysaccharides may play a critical role in monitoring the global nutritional status of the environment. In this work we analysed the role of DasA, the sugar-binding component of the chitobiose ATP-binding cassette transport system, in informing the cell of environmental conditions, and its role in the onset of development and in ensuring correct sporulation. The chromosomal interruption of dasA resulted in a carbon-source-dependent vegetative arrest phenotype, and we identified a second DasR-dependent sugar transporter, in addition to the N-acetylglucosamine phosphotransferase system (PTSGIcNAc), that relates primary metabolism to development. Under conditions that allowed sporulation, highly aberrant spores with many prematurely produced germ tubes were observed. While GIcNAc locks streptomycetes in the vegetative state, a high extracellular concentration of the GIcNAc polymer chitin has no effect on development. The striking distinction is due to a difference in the transporters responsible for the import of GIcNAc, which enters via the PTS, and of chitin, which enters as the hydrolytic product chitobiose (GIcNA(C2)) through the DasABC transporter. A model explaining the role of these two essentially different transport systems in the control of development is provided.