## 4 Discussion
Spore germination is likely to be triggered by the presence of specific nutrients. If one hypothesizes that such an advantage of IMOSs can be transposed in vivo to the level of the intestinal tract, then the association of the probiotic in the form of spores with a prebiotic IMOS substrate, poorly absorbed in the intestine, could make it possible to increase the supply of carbon sources available for the strain. We expect that IMOSs can favor the bioactivity of the probiotic within the gut microbiota and increase its beneficial effects on dysbiosis and intestinal disorders in animals [40; 44; 51]. Generally, in the presence of specific nutrient molecules, termed germinants, which are sensed by the spores' specific germinant receptors (GRs), the spores can rapidly return to active growth in the process of germination followed by outgrowth [52]. A study conducted by [PERSON] et al. [53] showed that the rates and efficiency of spore germination were greatly decreased when _B. cereus_ spores were prepared in a poor medium compared to a rich one. This hypothesis could also explain the beneficial effect of IMOSs on the probiotic germination. However, no effect on the germination of CU1 was observed in the absence of bile. In the presence of bile, DP1 no longer seemed to be the substrate preferentially used. DP2 appeared to be consumed first by the strain in small proportions. During further bacterial growth, DP2 was used simultaneously with glucose. These results suggest that a catabolic repression of IMOS use in the presence of glucose might be inhibited in the presence of bile. The role of carbohydrates in the mechanisms of bile resistance in the genus _Bacillus_ have not been well described to date. However, changes in carbohydrate metabolism in the presence of bile have been reported in _Bifidobacterium animals_ and _Bifidobacterium longum_ by [PERSON] et al. [54; 55; 56; 57]. Authors have reported an increased ATP production after incubation with bile through different pathways. While _B. longum_ increases ATP production through glycolysis, _B. animals_ increases substrate-level phosphorylation. A study conducted by [PERSON] et al. [58] demonstrated that the bile resistance of _B. breve_ and _B. longum_ increased if the medium contained FOS, rather than its monomeric components glucose and fructose. It would seem that the effect of bile can be limited by the addition of a carbon source whose metabolism allows the strain to set up energy-dependent detoxification mechanisms. It is possible that higher energy yields are obtained with oligosaccharides compared to those obtained with monosaccharides, thus contributing to a better resistance to bile. The influence of the carbon source on bile tolerance has also been studied by [PERSON] et al. [59]. The authors followed the growth and fermentation of _B. antimalarial_ subsp. _lactis_ IPLA 4549, and its bile-resistant counterpart, in a medium containing glucose or maltose as a carbon source. The authors highlighted that, in the absence of bile, maltose leads to a more favorable growth of the bile-resistant strain, compared to what is observed with glucose. The authors hypothesized that the resistant strain adapted its metabolism to increase ATP yields by preferentially using maltose, although it could still use glucose if the nutrient intake decreased. A proteomic study suggests that, for the bile-resistant strain, the \"D-fructose-6-phosphate shunt\" moves to other metabolic pathways, i.e., to the degradation of oxalic acid, which could theoretically increase ATP production [56]. A similar observation was also reported for _L. plantarum_ with an increase in a F0F1-ATP synthase expression in the presence of bile salts [60]. An extensive analysis is required to confirm these mechanisms in _B. subtilis_ CU1 in the presence of IMOSs. Taken together, our results suggest that IMOSs could be a good candidate to be associated with _B. subtilis_ CU1 in a symbiotic product, in order to improve bacteria physiology in the gut and the germination of spores in the presence of bile.