Aeromonas caviae motility and glycosylation

Aeromonas are Gram-negative facultative anaerobic rods, which inhabit various aquatic environments and are pathogens of both warm and cold-blooded animals. In humans they cause gastro-enteritis and wound infections. They are motile in liquid environments by a single polar type of flagellum. The flagellum plays an important role for the bacterial colonisation and the adhesion to the host cells. The Aeromonaspolar flagella filament is a polymer composed of two flagellins, FlaA and FlaB. The flagellins are O-linked glycosylated through the addition of the unusual bacterial sugar pseudaminic acid to serine and threonine residues within the flagellins D2/D3 domain. The addition of this sugar is essential for flagella filament assembly and bacterial motility. The flagellin’s are modified by between 6 – 8 sugar residues that occupy the potential 14 sites of attachment. Motility accessory factors (Maf proteins) are candidate enzymes for transferring glycan molecules to the flagellin (glycosyltransferases transferring sugar to flagellin) due to their genetic location and motility phenotypes associated with disruption mutants.

This study utilised site-directed mutagenesis to change the potential sites of flagellin glycosylation to assess the effect of these mutations on motility by swimming assays and flagella filament formation by electron microscopy. The analysis of different numbers of site-directed mutants suggest that some sites are more important than others and that the removal of 4 sites results in greatly reduced motility.