Chapter 29 : Characterization of a 16-Kilodalton Species-Specific Protein of Legionella pneumophila Promoting Uptake in Amoebae

Abstract:

Legionella pneumophila is the major agent responsible for Legionnaires' disease. To identify proteins that participate in the interaction of Legionella and its host, the authors screened a genomic library of L. pneumophila strain Corby with anti-Corby antiserum. P16-related proteins and p16 sequences were present exclusively in strains belonging to L. pneumophila. Characterization on the protein level was done by screening whole bacteria with MAb 61/1 as dot blot. The mutant showed the expected reaction type-loss of reactivity with the P16-specific monoclonal antibody. By comparing growth on the solid medium it was determined that p16 is not essential for growth of L. pneumophila and that genetic manipulations did not generate additional effects that influenced growth or colony morphology. To investigate the importance of L. pneumophila P16 for attachment, uptake, and/or intracellular growth in its different host cells, infection assays were performed in differentiated U937 cells and in Acanthamoeba castellanii. The wild-type phenotype was restored in the complemented mutant. From these results the authors speculate that the surface-exposed 16-kDa protein promotes the attachment/initial uptake and might act as an adhesin in the receptor-mediated uptake mechanism in amoebae. Further infection assays with other known Legionclla natural hosts will show whether the described locus p16 might be responsible for the broad host spectrum of L. pneumophila in contrast to the other species of Legionella.