Random mutagenesis of Legionella pneumophila reveals genes associated with lipopolysaccharide synthesis and recognition by typing monoclonal antibodies

AIMS: To use random mutagenesis for the characterization of Legionella pneumophila lipopolysaccharide (LPS) components and serotypes. METHODS AND RESULTS: Five strains belonging to different serogroups and/or monoclonal subgroups were mutagenized using a mini-Tn10 transposon. Exactly 11 819 mutants were checked for alterations in LPS using at least 11 monoclonal antibodies (mAbs) that define L. pneumophila serotypes. Among the mutants, five different mini-Tn10 insertions were identified. Four mutants originating from serogroup-1 did not lose their serogroup-specific epitope, but did sustain subtler changes that resulted in switches to different mAb subgroups. In contrast, a mutant from serogroup-6 lost its serogroup-specific epitope, while retaining a serogroup-cross-reacting epitope. CONCLUSIONS: Random mutagenesis is a valuable tool for LPS epitope mapping. While some characteristics of L. pneumophila LPS can be altered, others appear resistant to mutagenesis. This underscores both the flexibility and rigidity of LPS architecture in L. pneumophila. SIGNIFICANCE AND IMPACT OF THE STUDY: Losses of L. pneumophila LPS epitopes can result in new serotypes, changes that might escape detection by current DNA-based typing schemes. But, as the frequency of these changes is rare, based upon our observations, serotyping should remain an important tool for identifying L. pneumophila in water systems that are implicated in human infection.