Lipopolysaccharide biosynthetic locus as a source of clonal variation in Legionella pneumophila isolates associated with the outbreak in Japan

Some genomic subtypes of Legionella pneumophila exist in the environment that cause outbreaks. We examined how the clonal strains diverged through changes in their genomic structures using isolates associated with similar Pulsed-field gel electrophoresis patterns reported in the previous outbreak, serogroup (SG) 1 and SG13. The complete genomes for eight L. pneumophila SG1 and SG13 isolates were determined, and their genome structures were compared. A comparison of the complete genomes showed that these isolates had highly similar sequences, except for the region containing the lipopolysaccharide (LPS) biosynthetic locus, and IS1182 elements were present at both ends of the LPS biosynthetic locus in the SG1 isolates. We deduced that the SG13 isolates transformed into the SG1 isolates through recombination at the LPS biosynthetic locus involving IS1182 elements. It is important to consider the possibility that isolates associated with an outbreak of Legionella bacteria, despite having differing SGs, might be genetically related.