What enables a pathobiont to translocate? - Transcriptomic adaptation and commensal interactions of E. gallinarum an autoimmune pathobiont

• Applicant: Dr. Nathalie Jasmin Becker
• Subject Area: Rheumatology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 570867298

Translocation of gut commensals to secondary lymphoid organs contributes to the pathogenesis of extraintestinal autoimmune diseases such as systemic lupus erythematosus (SLE). Recently, different Enterococcus gallinarum strains have been identified as translocating depending on their within-host evolution. The liver translocating strain (EG1) was able to evade the immune system and increased inflammation and systemic autoimmunity in a murine model. On the contrary, the faecal strain (EG F2) was much less likely to breach the gut barrier. After translocation, rapid immune-mediated eradication seems to be circumvented by unknown mechanisms. The proposed project aims to elucidate the underlying mechanisms of how E. gallinarum can translocate and survive outside the gut. To this end, the study approaches the underlying bacterial pathomechanisms considering two different perspectives. The focal point of the first subproject is the initial phase of translocation through the gut barrier and the potential influence of the microbial environment. Growing evidence underlines the strong influence of microbiome composition on the pathogenicity of individual commensals. Therefore, we hypothesize that analogous influences on the translocation of E. gallinarum exist. To test this hypothesis, distinct microbiome compositions are created in each mouse using different antibiotic treatments. These altered microbiomes will serve as the background microbiome when EG1 is added to the community by gavage. Liver translocation, liver clearance of E. gallinarum and epithelial integrity will be assed. If changes are identified in one group, the composition of its microbiome background community will be defined in detail via 16S rRNA gene sequencing. Identified commensal interactions will be compared with publicly available human large-cohort studies to assess the feasibility in humans and experimentally confirmed in co-colonized gnotobiotic mice. The second subproject will analyze the transcriptomic adaptation of E. gallinarum in extraintestinal tissue. Reported mutations of EG1 were found in genes responsible for environmental sensing. We hypothesize that E. gallinarum undergoes changes in its transcriptional state on its way to the liver to adapt to different tissue and gain an advantage to proceed and survive. Therefore, I will implement novel methodologies, such as bacterial MERFISH, within a simplified monocolonized in vivo model. This will allow for the definition of transcriptomic phenotypes. Afterwards, transcriptomic states will be confirmed and analyzed in a more authentic murine model with a microbiome background. Overall, revealing the microbial mechanisms underlying the translocation of this pathobiont could represent a significant step towards understanding the triggers of autoimmune diseases such as SLE. These findings could contribute to the development of novel treatment options by altering the microbiome composition or influencing bacterial adaptation.

• DFG Programme: WBP Fellowship
• International Connection: USA
• Host: Professor Noah Wolcott Palm, Ph.D.