Identification and characterisation of a biosynthetic locus for Moraxella bovis lipo-oligosaccharide

Moraxella ovis and Moraxella bovoculi lipooligosaccharide biosynthesis genes, and structural characterisation of oligosaccharide from M. ovis 354T

Moraxella ovis is a Gram-negative bacterium isolated from sheep conjunctivitis cases and is a rare isolate of infectious bovine keratoconjunctivitis (IBK). This species is closely related to M. bovoculi, another species which can also be isolated from IBK, or cattle upper respiratory tract (URT). Prior to molecular identification techniques, M. bovoculi was frequently misclassified as M. ovis. We previously described the structure of two oligosaccharides (lipooligosaccharide-derived, minor and major glycoforms) from M. bovoculi 237T (type strain, also ATCC BAA-1259T). Here, we have identified the genetic loci for lipooligosaccharide synthesis in M. ovis 354T (NCTC11227) and compared it with M. bovoculi 237T. We identified genes encoding the known glycosyltransferases Lgt6 and Lgt3 in M.ovis. These genes are conserved in Moraxella spp., including M bovoculi. We identified three further putative OS biosynthesis genes that are restricted to M. ovis and M. bovoculi. These encode enzymes predicted to function as GDP-mannose synthases, namely a mannosyltransferase and a glycosyltransferase. Adding insight into the genetic relatedness of M.ovis and M. bovoculi, the M. ovis genes have higher similarity to those in M. bovoculi genotype 2 (nasopharyngeal isolates from asymptomatic cattle), than to M. bovoculi genotype 1 (isolates from eyes of IBK-affected cattle). Sequence analysis confirmed that the predicted mannosyltransferase in M. bovoculi 237T is interrupted by a C>T polymorphism. This mutation is not present in other M. bovoculi strains sequenced to date. We isolated and characterised LOS-derived oligosaccharide from M. ovis 354T. GLC-MS and NMR spectroscopy data revealed a heptasaccharide structure with three β-D-Glcp residues attached as branches to the central 3,4,6-α-D-Glcp, with subsequent attachment to Kdo. This inner core arrangement is consistent with the action of Lgt6 and Lgt3 glycosyltransferases. Two α-D-Manp residues are linearly attached to the 4-linked β-D-Glcp, consistent with the presence of the two identified glycosyltransferases. This oligosaccharide structure is consistent with the previously reported minor glycoform isolated from M. bovoculi 237T.

Structural characterisation of the oligosaccharide from Moraxella bovoculi type strain 237 (ATCC BAA-1259) lipooligosaccharide

The Gram-negative bacterium Moraxella bovoculi is associated with infectious bovine keratoconjunctivitis (IBK), colloquially known as 'pink-eye'. IBK is an extremely contagious ocular disease of cattle. We report here the structure of the oligosaccharide derived from the lipooligosaccharide from M. bovoculi type strain 237 (also known as ATCC BAA-1259T). GLC-MS and correlation NMR analysis of the oligosaccharide revealed 5 sugar residues, with a notable central branched 3,4,6-α-D-Glcp. An additional α-D-Manp was present ~30% on the sub-terminal α-D-Manp of the 4-linked branch. This oligosaccharide structure was consistent with other members of the Moraxellaceae where no heptose was present and 5-linked Kdo was directly attached to the central 3,4,6-α-D-Glcp.