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Characterization of legiolysin (lly), responsible for haemolytic activity, colour production and fluorescence of Legionella pneumophila

A genomic library of Legionella pneumophila, the causative agent of Legionnaires’disease in humans was constructed in Escherichia coli K12 and the recombinant clones were tested for haemolysis and other phenotypic properties. Seven clones were identified which were able to confer haemolysis of human, sheep, and canine erythrocytes but which were unable to mediate proteolytic activities or cyto‐toxic effects on CHO‐ or Vero cells. Clones that exhibited this haemolytic property were also able to produce a brown colour and a yellow‐green fluorescence activity detected on M9 plates containing tyrosine. The genetic determinant encoding these properties, termed legiolysin (lly) was mapped by Tn 1000 mutagenesis and by subcloning experiments. Southern hybridization with an lly‐specific gene probe showed that this determinant is part of the genome of L. pneumophila but is not identical to a protease gene of L. pneumophila which also mediates haemolysis. Minicell analysis of lly‐specific plasmids exhibited a protein of 39kDa. Polyclonal antibodies generated against a LacZ‐Lly hybrid protein also recognized a 39kDa protein produced either by the recombinant legiolysin‐positive E. coli K12 clones or by L. pneumophila wild‐type strains.