Shigella's c-di-GMP specific PDEs Modulate Biofilm and Virulence Phenotypes

To establish infection and cause disease, the intracellular pathogen Shigella must successfully navigate a series of host defenses and distinct microenvironments within the human body. One way Shigella navigates these enviroments is by using the secondary messenger c-di-GMP, which regulates many different bacterial behaviours. C-di-GMP is synthesized by diguanylate cyclases (DGCs) and broken down by c-di-GMP specific phosphodiesterases (PDEs). In this study, we investigated how Shigella's c-di-GMP specific PDEs impact c-di-GMP turn-over and subsequently biofilm and virulence phenotypes. We knocked out each of Shigella's six c-di-GMP specific PDEs to determine how these PDEs impact biofilm, virulence and c-di-GMP levels within the bacterial cell. We found that these PDEs negatively regulate c-di-GMP levels while modulating Shigella's virulence and biofilm behaviour. We also noted that altering expression of these Shigella PDEs changes bacterial cell size. Transcriptome analysis revealed that a Shigella ΔpdeB strain showed reduced expression of many genes, including the virulence genes ipgD and ipgE, as well as genes associated with lipid metabolism. We confirmed that a Shigella ΔpdeB strain had altered levels of stearic acid, and expression of pdeB alters Shigella antibiotic susceptibility. This study highlights the complexities of c-di-GMP signaling in regulating numerous Shigella pathways.