Legionella waltersii sp. nov. and an Unnamed Legionella Genomospecies Isolated from Water in Australia

Researchers isolated two Legionella-like organisms from water samples in Adelaide, Australia—one from a drinking water distribution system and another from a cooling tower at a sewage treatment plant. Both strains required L-cysteine for growth and displayed cellular characteristics typical of the Legionella genus, including branched-chain fatty acids and ubiquinones. Using DNA hybridization studies, the researchers determined that strain 2074-AUS-ET represented a new species, designated Legionella waltersii sp. nov., showing less than 10% DNA relatedness to all previously known Legionella species. Strain 2055-AUS-E was designated Legionella genomospecies 1 because, although it was genetically distinct from known species (53–69% related to L. quinlivanii), it could not be differentiated biochemically or serologically from L. quinlivanii serogroup 2. The two isolates were serologically distinct from each other and from all other characterized Legionella species by slide agglutination testing. These findings expand the known diversity of Legionella species found in Australian water environments.

Key findings

• Strain 2074-AUS-ET represents a new Legionella species, L. waltersii sp. nov., with less than 10% DNA relatedness to all previously described Legionella species
• Strain 2055-AUS-E was designated Legionella genomospecies 1; it is 53–69% related to L. quinlivanii at optimal DNA reassociation temperature but indistinguishable biochemically and serologically from L. quinlivanii serogroup 2
• Both isolates displayed typical Legionella characteristics including L-cysteine requirement, branched-chain fatty acids, and ubiquinones with 10 or more isoprene units
• L. waltersii can be differentiated from other Legionella species by its unique cellular fatty acid profile, particularly the presence of i-14:0 as a major component (13%)
• The two organisms were isolated from different water sources in Adelaide, Australia, representing previously unknown Legionella diversity in that region