Characterization of the Serogroup O11 O-Antigen Locus of Pseudomonas aeruginosa PA103

We previously cloned a genomic DNA fragment from the serogroup O11 Pseudomonas aeruginosa strain PA103 that contained all genes necessary for O-antigen synthesis and directed the expression of serogroup O11 antigen on recombinant Escherichia coli and Salmonella. To elucidate the pathway of serogroup O11 antigen synthesis, the nucleotide sequence of the biosynthetic genes was determined. Eleven open reading frames likely to be involved in serogroup O11 O-antigen biosynthesis were identified and are designated in order as wzz(PaO111) (wzz from P. aeruginosa serogroup O11), wzx(PaO11), wbjA, wzy(PaO11), wbjB to wbjF, wbpL(O11) and wbpM(O11) (wbpL and wbpM from serogroup O11). Consistent with previous descriptions of O-antigen biosynthetic gene loci, the entire region with the exception of wbpM(O11) has a markedly reduced G+C content relative to the chromosomal average. Wzy(PaO11) shows no significant similarity at the protein or DNA sequence level to any database sequence and is very hydrophobic, with 10 to 12 putative transmembrane domains, both typical characteristics of O-antigen polymerases. A nonpolar chromosomal insertion mutation in wzy(PaO11) in P. aeruginosa PA103 confirmed the identity of this gene. There is striking similarity between WbjBCDE and Cap(5/8)EFGL, involved in type 5 and type 8 capsule biosynthesis in Staphylococcus aureus. There is nearly total identity between wbpM(O11) and wbpM(O5), previously shown by others to be present in all 20 P. aeruginosa serogroups. Using similarity searches, we have assigned functions to the proteins encoded by the PA103 O-antigen locus and present the potential steps in the pathway for the biosynthesis of P. aeruginosa serogroup O11 O antigen.