Identification of proteins involved in the anti-inflammatory properties of Propionibacterium freudenreichii by means of a multi-strain study

Propionibacterium freudenreichii, a dairy starter, can reach a population of almost 109 propionibacteriaper gram in Swiss-type cheese at the time of consumption. Also consumed as a probiotic, it displaysstrain-dependent anti-inflammatory properties mediated by surface proteins that induce IL-10 inleukocytes. We selected 23 strains with varied anti-inflammatory potentials in order to identify theprotein(s) involved. After comparative genomic analysis, 12 of these strains were further analysed bysurface proteomics, eight of them being further submitted to transcriptomics. The omics data werethen correlated to the anti-inflammatory potential evaluated by IL-10 induction. This comparativeomics strategy highlighted candidate genes that were further subjected to gene-inactivationvalidation. This validation confirmed the contribution of surface proteins, including SlpB and SlpE, twoproteins with SLH domains known to mediate non-covalent anchorage to the cell-wall. Interestingly,HsdM3, predicted as cytoplasmic and involved in DNA modification, was shown to contribute toanti-inflammatory activity. Finally, we demonstrated that a single protein cannot explain the antiinflammatoryproperties of a strain. These properties therefore result from different combinationsof surface and cytoplasmic proteins, depending on the strain. Our enhanced understanding of themolecular bases for immunomodulation will enable the relevant screening for bacterial resources withanti-inflammatory properties