SAME SAME Cell and Molecular Biology section/symposium Oral/poster presentation Student The role of AlgX carbohydrate-binding module during alginate biosynthesis in Pseudomonas aeruginosa, Cystic fibrosis is a chronic, progressive, and often fatal genetic inherited disease caused by mutations in the gene that encodes the cystic fibrosis transmembrane conductance regulator (CFTR). Alginate or mucoid encapsulated Pseudomonas aeruginosa is the causative agent of respiratory insufficiency and failure in patients with cystic fibrosis. We have previously reported that AlgX is a protein required for alginate biosynthesis. Recently, AlgX has been reported to play a role in the modification of alginate through acetylation. In this study, we show that the absence of AlgX resulted in the loss of mucoidy due to the degradation of nascent alginate by the alginate lyase, AlgL. Using computational molecular docking studies and alginate affinity assay, we show that AlgX binds alginate via the carbohydrate-binding module located in the C-terminal region. Alanine mutations of the predicted amino acid residues that interact with alginate suggest that K338, R370, T372, and R380 are important for alginate binding. Alginate rescue assay by in trans expression of mutant AlgX in a chromosomal algX deleted P. aeruginosa mutant confirms the importance of these amino acid residues during alginate biosynthesis. In summary, these studies suggest that AlgX protects the alginate polymers from AlgL degradation, binds alginate via the carbohydrate-binding module, and is conceivably located in the biosynthetic scaffold serving as an appendage to the alginate acetylation machinery. In conclusion, AlgX binds alginate via the carbohydrate-binding module and is required for alginate biosynthesis and modification. Abstract contains 236/250 words