Highly Dynamic Genomic Loci Drive the Synthesis of Two Types of Capsular or Secreted Polysaccharides within the Mycoplasma mycoides Cluster

Abstract

ABSTRACTMycoplasmas of theMycoplasma mycoidescluster are all ruminant pathogens.Mycoplasma mycoidessubsp.mycoidesis responsible for contagious bovine pleuropneumonia and is known to produce capsular polysaccharide (CPS) and exopolysaccharide (EPS). Previous studies have strongly suggested a role forMycoplasma mycoidessubsp.mycoidespolysaccharides in pathogenicity.Mycoplasma mycoidessubsp.mycoides-secreted EPS was recently characterized as a β(1→6)-galactofuranose homopolymer (galactan) identical to the capsular product. Here, we extended the characterization of secreted polysaccharides to all other members of theM. mycoidescluster:M. capricolumsubsp.capripneumoniae,M. capricolumsubsp.capricolum,M. leachii, andM. mycoidessubsp.capri(including the LC and Capri serovars). Extracted EPS was characterized by nuclear magnetic resonance, resulting in the identification of a homopolymer of β(1→2)-glucopyranose (glucan) inM. capricolumsubsp.capripneumoniaeandM. leachii. Monoclonal antibodies specific for this glucan and for theMycoplasma mycoidessubsp.mycoides-secreted galactan were used to detect the two polysaccharides. WhileM. mycoidessubsp.capristrains of serovar LC produced only capsular galactan, no polysaccharide could be detected in strains of serovar Capri. All strains ofM. capricolumsubsp.capripneumoniaeandM. leachiiproduced glucan CPS and EPS, whereas glucan production and localization varied amongM. capricolumsubsp.capricolumstrains. Genes associated with polysaccharide synthesis and forming a biosynthetic pathway were predicted in all cluster members. These genes were organized in clusters within two loci representing genetic variability hot spots. Phylogenetic analysis showed that some of these genes, notablygalEandglf, were acquired via horizontal gene transfer. These findings call for a reassessment of the specificity of the serological tests based on mycoplasma polysaccharides.