We describe phenotypic and genetic characterization of an atypical Japanese Actinobacillus pleuropneumoniae isolate OT761. Nucleotide sequence analysis revealed that gene clusters involved in capsular polysaccharide and O-polysaccharide (O-PS) biosynthesis of the isolate were nearly identical to those of serovar 2 reference strain. The main difference found between the O-PS loci is the shortening of 31 amino acids from the C terminus of WcaJ in the atypical isolate due to a 93 bp deletion at the 3' end of wcaJ gene. Immunoblot analysis revealed that this isolate could not produce O-PS. Taken together, our results showed that the C-terminal domain of the A. pleuropneumoniae WcaJ plays a critical role in enzyme function of WcaJ involved in the biosynthesis of O-PS.
Keywords: Actinobacillus pleuropneumoniae; atypical; rough-type lipopolysaccharide; swine; wcaJ.