Glycosyltransferases (GTs) play a pivotal role in synthesizing essential glycoconjugates, with cellulose and chitin synthases in the GTs family 2 being key enzymes in biopolymer synthesis. Traditionally, these enzymes are considered organism-specific with distinct substrate specificities. This study challenges this paradigm by demonstrating the substrate promiscuity of bacterial cellulose synthase from Rhodobacter sphaeroides (rBscA-B). We present findings showing that rBscA-B can cleave uridine diphosphate N-acetylglucosamine (UDP-α-D-GlcNAc), albeit with lower substrate affinity and efficiency compared to its natural substrate, uridine diphosphate. When R. sphaeroides is grown with UDP-α-D-GlcNAc, it results in the production of chitin oligomers, deviating from its conventional role in cellulose synthesis. These results not only challenge the established view of strict organism-specific biopolymer synthesis but also open up new avenues for biotechnological exploitation in modifying cellulose composition in bacterial systems with implications for understanding evolutionary adaptations in biopolymer synthesis enzymes.