Conclusions

Genomics has provided a wealth of new information about L. pneumophila and enriches our knowledge about this important organism. Comparative genomics has uncovered a large number of genome rearrangements such as inversions, insertions of large DNA fragments, but also deletions and insertions of smaller fragments, some of which show characteristics of pathogenicity (genomic) islands which exhibit a Legionella-specific mosaic structure. The high genomic plasticity and versatility is probably a mechanism of L. pneumophila to adapt to changing environments.

Genome analysis has identified a large number of proteins predicted to modulate host cell functions and to allow L. pneumophila to subvert host functions to its advantage. This role might be achieved in part by the many eukaryotic-like proteins or eukaryotic protein domains identified for the first time in a prokaryotic genome. The particularly large number and wide variety of secretion systems present in the genomes should allow effective delivery of the substrates.

Given the genetic diversity and genomic plasticity identified through genome comparison, it is clear that additional knowledge about the genetic basis of different L. pneumophila strains and of other Legionella species is needed. New, powerful genomics approaches based on the available sequences like microarray techniques for comparative genomics should now be applied to reveal further differences as well as for the functional analysis of gene expression. The next scientific challenge will be to use this information to elucidate the virulence and adaptation mechanisms of L. pneumophila in order to combat legionellosis and to allow effective elimination of this pathogen from water systems and aerosol producing systems.

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