Expression and Genetic Activation of Cyclic Di-GMP-Specific Phosphodiesterases in Escherichia coli

Intracellular levels of the bacterial second messenger c-di-GMP are controlled by antagonistic activities of diguanylate cyclases and phosphodiesterases. The phosphodiesterase PdeH was identified as a key regulator of motility in E. coli, while deletions of any of the other 12 genes encoding for potential phosphodiesterases did not interfere with motility. To analyze the role of E. coli phosphodiesterases, we demonstrated that under laboratory conditions most of these proteins are expressed. We next isolated suppressor mutations in six phosphodiesterase genes, which reinstate motility in the absence of PdeH by reducing cellular levels of c-di-GMP. Expression of all mutant alleles also led to a reduction of biofilm formation. Thus, all of these proteins are bona fide phosphodiesterases that are capable of interfering with different c-di-GMP responsive output systems by affecting the global c-di-GMP pool. This argues that E. coli possesses several phosphodiesterases that under laboratory conditions are inactive because they lack appropriate input signals.Finally, one of these phosphodiesterases, PdeL, was studied in more detail. We demonstrated that this protein acts as transcription factor to control its own expression. Motile suppressor alleles led to a strong increase of PdeL activity and elevated pdeL transcription, suggesting that enzymatic activity and transcriptional control are coupled. In agreement with this, we show that overall cellular levels of c-di-GMP control pdeL transcription and that this control depends on PdeL itself. We thus propose that PdeL acts both as an enzyme and c-di-GMP sensor to couple transcriptional activity to the c-di-GMP status of the cell.; Most bacteria possess multiple diguanylate cyclases and phosphodiesterases. Genetic studies have proposed that these enzymes show signaling specificity by contributing to distinct cellular processes without much crosstalk. Thus, spatial separation of individual c-di-GMP signaling units was postulated. However, since most cyclases and phosphodiesterases harbor N-terminal signal input domains, it is equally possible that under laboratory conditions most of these enzymes lack their activating signals thereby simulating signaling specificity on genetic level. We demonstrate that a subset of E. coli phosphodiesterases can be genetically activated to affect the global c-di-GMP pool and by that influence different c-di-GMP dependent processes. Although this does not exclude spatial confinement of individual phosphodiesterases, this study emphasizes the importance of environmental signals for activation of phosphodiesterases.