Cellulose is the most abundant organic polymer in nature being a structural component of the cell wall of most plants. This highly insoluble polymer is degraded by filamentous fungi and actinomycetes, which secrete numerous enzymes tailored to fulfill this task. Streptomyces coelicolor is the best-studied representative of the actinomycetes, and a model organism for understanding prokaryotic development. It forms reproductive aerial hyphae after a period of assimilative growth. Unexpectedly, we identified a classical cellulose synthase gene whose inactivation critically impaired development on a wide range of media. Also, expression of this gene is strongly induced upon initiation of development indicating a key role for this enzyme during morphogenesis. Taken together, I propose that the cellulose synthase has a structural role in development by producing cellulose, which is incorporated in the cell walls of growing aerial hyphae. This could therefore represent the first example of bacterial cell walls that contain cellulose. Besides having an important role during formation of aerial hyphae, cellulose might have a second distinct function during attachment of Streptomyces hyphae to solid surfaces. Strong attachment involves the formation of an uncharacterized extracellular matrix of thin fibrillar structures associated with the adhering hyphae. This matrix strongly resembles that formed by various pathogenic bacteria, in which it was shown to consist of amyloid-like fibrils in association with cellulose. This proposal is aimed at elucidating the role of the cellulose synthase enzyme in morphogenesis and attachment of S. coelicolor. This research provides important new insights how structural modifications to bacterial cell walls affect microbial development. The host institute’s broad knowledge of actinomycetes and carbohydrate biology, and the experience of the researcher with prokaryotic development make this collaboration potentially highly fruitful