Salmonella enterica Serovar Typhimurium Can Detect Acyl Homoserine Lactone Production by Yersinia enterocolitica in Mice

LuxR-type transcription factors detect acyl homoserine lactones (AHLs) and are typically used by bacteria to determine the population density of their own species.Escherichia coli andSalmonella enterica serovar Typhimurium cannot synthesize AHLs but can detect the AHLs produced by other bacterial species using the LuxR homolog, SdiA. Previously we determined thatS. Typhimurium did not detect AHLs during transit through the gastrointestinal tract of a guinea pig, a rabbit, a cow, 5 mice, 6 pigs, or 12 chickens. However, SdiA was activated during transit through turtles colonized byAeromonas hydrophila , leading to the hypothesis that SdiA is used for detecting the AHL production of other pathogens. In this report, we determined that SdiA is activated during the transit ofS. Typhimurium through mice infected with the AHL-producing pathogenYersinia enterocolitica . SdiA is not activated during transit through mice infected with ayenI mutant ofY. enterocolitica that cannot synthesize AHLs. However, activation of SdiA did not confer a fitness advantage inYersinia -infected mice. We hypothesized that this is due to infrequent or short interactions betweenS. Typhimurium andY. enterocolitica or that the SdiA regulon members do not function in mice. To test these hypotheses, we constructed anS. Typhimurium strain that synthesizes AHLs to mimic a constant interaction withY. enterocolitica . In this background,sdiA + S. Typhimurium rapidly outcompetes thesdiA mutant in mice. All known members of thesdiA regulon are required for this phenotype. Thus, all members of thesdiA regulon are functional in mice.