In vitro assessment of Bacillus subtilis DSM29784 secreted metabolites on gut chicken microbiota

In poultry, the probiotic Bacillus subtilis 29784 (Bs29784) sustains
intestinal health, enhancing animal resilience and performance through the
production of the bioactive metabolites hypoxanthine (HPX), Niacin (NA),
and pantothenate (PTH). Here, using enterocyte in vitro models, we
determine the functional link between these metabolites and the three
pillars of intestinal resilience: immune response, intestinal barrier, and
microbiota. To this end, we evaluated in vitro Bs29784 vegetative cells,
spores, and metabolites capacity to modulate global immune regulators
(using HT-29-NF-κB and HT-29-AP1 reporter cells), intestinal integrity
(HT-29-MUC-2 reporter cells and Caco-2 cells), and cytokine production
(Caco-2 cells). Finally, we simulated chickens’ intestinal fermentations
to determine the effect of Bs29784 metabolites on the microbiota and their
fermentation profile. Bs29784 vegetative cells reduce the inflammatory
response more effectively than spores, indicating that their benefit is
linked to metabolic activity. To assess this hypothesis, we studied
individually Bs29784 metabolites. The results show that each metabolite
had different beneficial effects. PTH and NIA reduced the activation of
the proinflammatory pathways AP1 and NF-κB. HPX upregulated mucin
production by enhancing MUC2 expression. HPX, NA, and PTH increased cell
proliferation. PTH and HPX increased epithelial resilience to an
inflammatory challenge by limiting permeability increase. In cecal
fermentations NA increased acetate, HPX increased butyrate while PTH
increased acetate, butyrate, and propionate. In ileal fermentations, PTH
increased butyrate. All molecules lead changes to microbiota explaining
the different fermentation patterns. Altogether, we show that Bs29784
modulates intestinal health by acting on the three lines of resilience via
its secreted metabolites.