Regulation of Salmonella virulence by interspecies methylthioadenosine signaling

AbstractPathogenic bacteria within a mammalian host are bombarded by intercellular, interspecies, and cross-kingdomsignaling molecules and metabolites. For Salmonella enterica, multiple signals, including pH, bile, and shortchain fatty acids, regulate Salmonella Pathogenicity Island I (SPI-1) to trigger invasion and inflammation in thegut. Recently, our lab demonstrated that the methionine-derived metabolite methylthioadenosine (MTA) is apreviously unrecognized signal produced by the host and pathogen that suppresses SPI-1, flagellar motility, andin vivo virulence. These conclusions were drawn from experiments treating S. Typhimurium with MTA and bycharacterizing a mutant with increased endogenous MTA. This mutant lacks the master repressor of themethionine metabolism pathway, metJ. In addition to MTA?s effect on S. Typhimurium, MTA also modulates hostresponses and is released into plasma during S. Typhimurium infection in mice and during sepsis in humans.Thus, MTA can suppress S. Typhimurium virulence and its levels in the host undergo dramatic shifts duringinfection. However, it is unknown if and how host- or microbiota-produced MTA signals to S. Typhimurium at thecrucial initial site of this host-pathogen conflict, the intestinal lumen. We hypothesize that MTA in the intestine isdynamically regulated by host, commensal microbiota, and pathogen, and that shifts in MTA levels are sensedby Salmonella to regulate virulence gene expression. Therefore, the first goal of this project is to characterizecontributions and consequences of host- and microbial-derived MTA during S. Typhimurium infection. MTAlevels in gut contents and tissue will be measured from germ-free and microbiome reconstituted mice at baselineand with S. Typhimurium infection. Furthermore, we will manipulate host MTA levels through exogenous MTAand the use of an inhibitor that specifically blocks host MTA metabolism. The second goal is to elucidatemechanisms of MTA suppression of S. Typhimurium virulence. We will test whether MTA modulates regulatorsof SPI-1 expression and if MTA facilitates broader gene expression changes through regulation of methylation.Completion of these aims will identify whether MTA acts as an interspecies signal in the gut and identify howMTA suppresses virulence. This work could improve clinical outcomes by demonstrating that existing methioninemetabolism inhibitors can suppress S. Typhimurium virulence.