Churaman, C. N. | Search bioRxiv

bioRxiv2026

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 Shigellas c-di-GMP specific PDEs impact c-di-GMP turn-over and subsequently biofilm and virulence phenotypes. We knocked out each of Shigellas 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 Shigellas virulence and biofilm behaviour. We also noted that altering expression of these Shigella PDEs changes bacterial cell size. Transcriptome analysis revealed that a Shigella {Delta}pdeB 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 {Delta}pdeB 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.

microbiology↗

bioRxiv2022

Vibrio cholerae alkalizes its environment via citrate metabolism to inhibit enteric growth

Vibrio cholerae is a Gram-negative pathogen, living in constant competition with other bacteria in both marine environments and during human infection. One competitive advantage of V. cholerae is the ability to metabolize diverse carbon sources such as chitin and citrate. We observed that when V. cholerae strains were grown on a medium with citrate, the mediums chemical composition turned into a hostile alkaline environment for Gram-negative bacteria such as Escherichia coli and Shigella flexneri. We found that although the ability to exclude competing bacteria was not contingent on exogenous citrate, V. cholerae citrate metabolism mutants {Delta}oadA-1, {Delta}citE, and {Delta}citF mutants were not able to inhibit S. flexneri or E. coli growth. Lastly, we demonstrated that while the V. cholerae mediated increased medium pH was necessary for the enteric exclusion phenotype, secondary metabolites such as bicarbonate (protonated to carbonate in the raised pH) from the metabolism of citrate enhanced the ability to inhibit the growth of E. coli. These data provide a novel example of how V. cholerae outcompetes other Gram-negative bacteria.

microbiology↗