Regulation of Dot-Icm effectors translocation by T4SS GGDEF-EAL proteins in Legionella pneumophila

Legionella pneumophila is a waterborne bacterium that can replicate in a variety of host cells (from environmental amoebae to human macrophages). Its virulence traits are subject to complex regulation that involves some signaling pathways dependent on cyclic di-GMP. Cyclic di-GMP is a second messenger that can result in transcriptional, translational or post-translational control of targets including secretion systems. We are particularly interested in the c-di-GMP metabolizing enzyme Lpl0780/Lpp0809 needed for the early steps of intracellular cycle and the appropriate translocation of bacterial effectors by Dot/Icm T4SS. Comparative transcriptomic analysis was performed from the RNA-seq data of the Lens Wild-Type strain and the ?lpl0780 mutant using DESeq2 package on normalized gene read counts. The results showed that only 12 genes (among 2966) were significantly differentially expressed (P < 0.01 and log2 fold change of >1 or <-1) between ?lpl0780 strain and the WT Lens strain. However, the fold changes remain quite weak and moreover none of these genes can be connected to T4SS or effectors. These results suggest that Lpl0780/Lpp0809 acts at a post-transcriptional level on the translocation of effectors.