Comparative genomic analysis of the flagellin glycosylation island of the Gram-positive thermophile Geobacillus

Background: Protein glycosylation involves the post-translational attachment of sugar chains to target proteins and has been observed in all three domains of life. Post-translational glycosylation of flagellin, the main structural protein of the flagellum, is a common characteristic among many Gram-negative bacteria and Archaea. Several distinct functions have been ascribed to flagellin glycosylation, including stabilisation and maintenance of the flagellar filament, motility, surface recognition, adhesion, and virulence. However, little is known about this trait among Gram-positive bacteria. Results: Using comparative genomic approaches the flagellin glycosylation loci of multiple strains of the Gram-positive thermophilic genus Geobacillus were identified and characterized. Eighteen of thirty-six compared strains of the genus carry these loci, which show evidence of horizontal acquisition. The Geobacillus flagellin glycosylation islands (FGIs) can be clustered into five distinct types, which are predicted to encode highly variable glycans decorated with distinct and heavily modified sugars. Conclusions: Our comparative genomic analyses showed that, while not universal, flagellin glycosylation islands are relatively common among members of the genus Geobacillus and that the encoded flagellin glycans are highly variable. This suggests that flagellin glycosylation plays an important role in the lifestyles of members of this thermophilic genus.