Pseudomonas aeruginosais an opportunistic Gram-negative bacterium that causes severe infections in a number of hosts from plants to mammals. A-band lipopolysaccharide of P. aeruginosacontains D-rhamnosylated O-antigen. The synthesis of GDP-D-rhamnose, the D-rhamnose donor in D-rhamnosylation, starts from GDP-D-mannose.