Biology subjects

Payne, S. M.

Publications and source records attributed to Payne, S. M..

3 recordsLinked to original sources

bioRxiv2023

(p)ppGpp is required for Virulence of Shigella flexneri

Infection by the enteric pathogen Shigella flexneri requires transit through the gastrointestinal tract and invasion of and replication within the cells of the host colonic epithelium. This process exposes the pathogen to a range of diverse microenvironments. Further, the unique composition and physical environment of the eukaryotic cell cytosol represents a stressful environment for S. flexneri, and extensive physiological adaptations are needed for the bacterium to thrive. In this work, we show that disrupting synthesis of the stringent response alarmone (p)ppGpp in S. flexneri diminished expression of key virulence genes, including ipaA, ipaB, ipaC and icsA, and it reduced bacterial invasion and intercellular spread. Deletion of the (p)ppGpp synthase gene relA alone had no effect on S. flexneri virulence, but disruption of both relA and the (p)ppGpp synthase/hydrolase gene spoT resulted in loss of (p)ppGpp synthesis and virulence. While the relA spoT deletion mutant was able to invade a cultured human epithelial cell monolayer, albeit at reduced levels, it was unable to maintain the infection and spread to adjacent cells, as indicated by loss of plaque formation. Complementation with spoT on a plasmid vector restored plaque formation. Thus, SpoT alone is sufficient to provide the necessary level of (p)ppGpp for virulence. These results indicate that (p)ppGpp is required for S. flexneri virulence and adaptation to the intracellular environment, adding to the repertoire of signaling pathways that affect Shigella pathogenesis.

microbiology↗

bioRxiv2022

Bacteroides thetaiotaomicron outer membrane vesicles modulate virulence of Shigella flexneri

The role of the gut microbiota in the pathogenesis of Shigella flexneri remains largely unknown. To understand the impact of the gut microbiota on S. flexneri virulence, we examined the effect of interspecies interactions with Bacteroides thetaiotaomicron (Bt), a prominent member of the gut microbiota, on S. flexneri invasion. When grown in Bt conditioned medium, S. flexneri showed reduced invasion of human epithelial cells. This decrease in invasiveness of S. flexneri resulted from a reduction in the level of S. flexneris master virulence regulator VirF. Reduction of VirF corresponded with a decrease in expression of a secondary virulence regulator virB, as well as expression of S. flexneri virulence genes required for invasion, intracellular motility, and spread. Repression of S. flexneri virulence factors by Bt conditioned medium was not caused by either a secreted metabolite or protein, but rather, was due to the presence of Bt outer membrane vesicles (OMVs) in the conditioned medium. The addition of purified Bt OMVs to S. flexneri growth medium recapitulated the inhibitory effects of Bt conditioned medium on invasion, virulence gene expression, and virulence protein levels. Total lipids extracted from either Bt cells or Bt OMVs also recapitulated the effects of Bt condition medium on expression of the S. flexneri virulence factor IpaC, indicating that Bt OMV lipids, rather than a cargo contained in the vesicles, are the active factor responsible for the inhibition of S. flexneri virulence. ImportanceShigella flexneri is the causative agent of bacillary dysentery in humans. Shigella spp. are one of the leading causes of diarrheal morbidity and mortality, especially among children in low and middle-income countries. The rise of antimicrobial resistance combined with the lack of an effective vaccine for Shigella heightens the importance of studies aimed at better understanding previously uncharacterized aspects of Shigella pathogenesis. Here, we show that conditioned growth medium from the commensal bacteria Bacteroides thetaiotaomicron represses the invasion of S. flexneri. This repression is due to the presence of B. thetaiotaomicron outer membrane vesicles. These findings establish a role for interspecies interactions with a prominent member of the gut microbiota in modulating the virulence of S. flexneri and identify a novel function of outer membrane vesicles in interbacterial signaling between members of the gut microbiota and an enteric pathogen.

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↗