Analysis of glycosyldiacylglycerols produced by the zoonotic pathogen Streptococcus suis

Streptococcus suis is a major swine pathogen with zoonotic potential, responsible for substantial economic losses to the swine industry worldwide. The nature of its bacterial cell wall components and their role in virulence have not been fully elucidated yet. We herein report the isolation and structural characterization of the glycosyldiacylglycerols produced by S. suis. In four selected strains, we show the presence of 1,2-diacyl-3-O-(α-D-glucopyranosyl-(1→2)-α-D-glucopyranosyl)-sn-glycerol and 1,2-diacyl-3-O-(α-D-glucopyranosyl)-sn-glycerol, both frequently found in streptococci and some other bacteria. In addition, 1,2-diacyl-3-O-(β-D-galactofuranosyl)-sn-glycerol was identified in all investigated strains, a molecule only rarely described in other streptococci and so far not in other bacterial species. Enzymes putatively involved in the biosynthesis of these glycosyldiacylglycerols were identified by BLASTP homology search. Genes encoding these enzymes showed an important degree of conservation across a global S. suis strain collection, with BLASTN analysis revealing high nucleotide identity (mean 94.7-99.2%) and consistent near-complete query coverage. Together, these findings suggest that glycosyldiacylglycerol biosynthesis is broadly maintained across S. suis.