B-172. A Global Effect of the PmrAB Two Component System of Legionella pneumophila on Expression of Genes Required for Modulation of Cellular Processes
Legionella pneumophila multiplies within protozoa and human macrophages by utilizing the Dot/Icm type IV secretion system to evade the endosomal and lysosomal pathway. We have previously shown that L. pneumophila harbors at least 11 genes encoding eukaryotic ankyrin repeats-containing proteins (ank). To study the role of the PmrA/B two component system (TCS) in regulation of the ank genes and other genes, we have constructed isogenic pmrA and pmrB mutants by allelic exchange. Genome-wide microarray gene expression analyses of the pmrA/B mutants show that the PmrA/B TCS has a global effect on expression of genes encoding dot/icm effectors and many stress-related genes. Real-time qRT-PCR analyses show that PmrA is a positive regulator of all the ank genes. Alignment of the upstream region of the promoter region of the ank genes has revealed a regulatory consensus region for the PmrA binding site. In intracellular infections, the pmrB mutant exhibits a significant defect in Acanthamoeba polyphaga, the ciliate Tetrahymena pyriformis, human monocytes-derived macrophages, and the U937 macrophage cell line. The pmrA mutant was defective only in the ciliate, suggesting a protozoan host tropism directed by this TCS. Single cell analyses have shown that similar to the dot/icm mutants the intracellular growth defect of the pmrB mutant was totally rescued in-trans within communal phagosomes harboring the wild type strain. However, both pmrA and pmrB mutants exclude late endosome and lysosomal markers and recruit the RER. We conclude that the PmrAB TCS has a global effect on gene expression particularly novel genes that are involved in modulation of cellular processes.