Salmonella Typhimurium Strain ATCC14028 Requires H2-Hydrogenases for Growth in the Gut,but Not at Systemic Sites

Salmonella enterica is a common cause of diarrhea. For eliciting disease, the pathogen has to colonize the gut lumen, a site colonized by the microbiota. This process/initial stage is incompletely understood. Recent work established that one particular strain, Salmonella enterica subspecies 1 serovar Typhimurium strain SL1344, employs the hyb H₂-hydrogenase for consuming microbiota-derived H₂ to support gut luminal pathogen growth: Protons from the H₂-splitting reaction contribute to the proton gradient across the outer bacterial membrane which can be harvested for ATP production or for import of carbon sources. However, it remained unclear, if other Salmonella strains would use the same strategy. In particular, earlier work had left unanswered if strain ATCC14028 might use H₂ for growth at systemic sites. To clarify the role of the hydrogenases, it seems important to establish if H₂ is used at systemic sites or in the gut and if Salmonella strains may differ with respect to the host sites where they require H₂ in vivo. In order to resolve this, we constructed a strain lacking all three H₂-hydrogenases of ATCC14028 (14028^hyd3) and performed competitive infection experiments. Upon intragastric inoculation, 14028^hyd3 was present at 100-fold lower numbers than 14028^WT in the stool and at systemic sites. In contrast, i.v. inoculation led to equivalent systemic loads of 14028^hyd3 and the wild type strain. However, the pathogen population spreading to the gut lumen featured again up to 100-fold attenuation of 14028^hyd3. Therefore, ATCC14028 requires H₂-hydrogenases for growth in the gut lumen and not at systemic sites. This extends previous work on ATCC14028 and supports the notion that H₂-utilization might be a general feature of S. Typhimurium gut colonization.