Overexpresssion of a Legionella pneumophila homologue of the E-coli regulator csrA affects cell size, flagellation, and pigmentation

Legionella pneumophila is an inhabitant of the aquatic environment and the causative agent of a bacterial pneumonia. We identified the presence of an L. pneumophila homologue of csrA of E. coli and rsmA of Erwinia carotovora, genes which regulate gene expression by destabilising mRNA and which have been shown to relate to environmental fitness and pathogenicity. The Legion ella csrA was able to complement a csrA-negative mutant of E. coli. Overpro duction of csrA in L. pneumophila lead to a reduction of flagellation and p igmentation and an increase in bacterial cell size. csrA overproduction was associated with a reduction of fliA and flaA transcripts. This suggests th at similar to E. coli and Erwinia, L. pneumophila csrA is a regulator of ge ne expression and may contribute to the capability of the pathogen to rapid ly adapt to changing environments.