Use of transcriptome data to study the c-di-GMP signaling network in Pseudomonas aeruginosa clinical isolates
In the Pseudomonas aeruginosa type strain PA14, 40 genes are known to encode for diguanylate cyclases (DGCs) and/or phosphodiesterases (PDEs), which modulate the intracellular pool of the nucleotide second messenger c-di-GMP. While in general, high levels of c-di-GMP drive the switch from highly motile phenotypes towards a sessile lifestyle, the different c-di-GMP modulating enzymes are responsible for smaller and in parts non-overlapping phenotypes. In this study, we sought to utilize previously recorded P. aeruginosa gene expression datasets on 414 clinical isolates to uncover transcriptional changes as a result of a high expression of genes encoding diguanylate cyclases. We demonstrate that the selection of sub-groups of clinical isolates with high versus low expression of regulatory genes served the identification of their downstream regulons. Thus, analyzing transcriptional profiles of clinical isolates with variant expression of diguanylate cyclase genes might provide a unique opportunity to bypass the problem that for many c-di-GMP modulating enzymes it is not known under which conditions their expression is activated. However, because the high c-di-GMP associated phenotypes were rapidly lost in the clinical isolates, we were unable to confirm diguanylate specific gene regulation. It is possible that the elevated c-di-GMP concentrations observed in the clinical P. aeruginosa isolates were due to a memory response, in which the bacteria maintain a certain level of c-di-GMP even after being removed from the conditions that induced the production of c-di-GMP. Further studies would be needed to determine the specific mechanisms underlying this memory response in P. aeruginosa. Overall design: RNASeq of different Pseudomonas aeruginosa PA14/PAO1 and clinical isolates with a mutation in PA14_03790 or PA14_23130 - planctonic growth in LB medium.