Cellulose, a linear polysaccharide polymer, has a structural role in bacterial biofilms by providing a scaffold that protects and supports the growth of the biofilm. A recent study reported the structure of phosphoethanolamine cellulose, a modified cellulose that is produced by Escherichia coli and is required for extracellular matrix assembly and biofilm architecture. The authors used solid-state NMR spectroscopy to detect the phosphoethanolamine modification that had not been previously found using conventional methods. Part of the bacterial cellulose synthesis operon (the bcsEFG operon) was indispensable for the modification, and the putative phosphoethanolamine transferase BcsG was found to interact with the cellulose synthase complex and required input from the second messenger c-di-GMP through a BcsE-BcsF-BcsG signalling pathway. These findings have implications for the development of new cellulosic materials and biofilm formation.