A genomic island in Pseudomonas aeruginosa carries the determinants of flagellin glycosylation

Protein glycosylation has been long recognized as an important posttranslat ional modification process in eukaryotic cells. Glycoproteins, predominantl y secreted or surface localized, have also been identified in bacteria. We have identified a cluster of 14 genes, encoding the determinants of the fla gellin glycosylation machinery in Pseudomanas aeruginosa PAK, which we call ed the flagellin glycosylation island. Flagellin glycosylation can be detec ted only in bacteria expressing the a-type flagellin sequence variants, and the survey of 30 P. aeruginosa isolates revealed coinheritance of the a-ty pe flagellin genes with at feast one of the flagellin glycosylation island genes. Expression of the b-type flagellin in PAK, an a-type strain carrying the glycosylation island, did not lead to glycosylation of the b-type flag ellin of PAO1, suggesting that flagellins expressed by b-type bacteria not only lack the glycosylation island, they cannot serve as substrates for gly cosylation. Providing the entire glycosylation island of PAK, including its a-type flagellin in a flagellin mutant of a b-type strain, results in glyc osylation of the heterologous flagellin. These results suggest that some or all of the 14 genes on the glycosylation island are the genes that are mis sing from strain PAO1 to allow glycosylation of an appropriate flagellin. I nactivation of either one of the two flanking genes present on this island abolished flagellin glycosylation. Based on the limited homologies of these gene products with enzymes involved in glycosylation, we propose that the island encodes similar proteins involved in synthesis, activation, or polym erization of sugars that are necessary for flagellin glycosylation.