Alterations of the Viable Ileal Microbiota of the Gut Mucosa-Lymph Node Axis in Pigs Fed Phytase and Lactic Acid-Treated Cereals.

The gut-lymph node axis is a critical player in the symbiotic relationship between gut microbiota and the host. However, little is known about the impact of diet-related bacterial shifts in the gut lumen on bacterial translocation into lymph nodes. Here, we (i) characterized changes in the viable microbiota composition along the ileal digesta-mucosa-lymph node axis and (ii) examined the effect of dietary phytase supplementation and lactic acid (LA) soaking of cereals on the bacterial taxonomy along this axis, together with their effect on the mucosal expression of innate immune and barrier function genes in pigs (n = 8/diet). After 18 days on diets, ileal digesta, mucosa, and ileocecal lymph nodes (ICLNs) were collected for RNA isolation and 16S rRNA-based high-resolution community profiling. Bacterial communities were dominated by Lactobacillaceae and Clostridiaceae, with clearly distinguishable profiles at the three sampling sites. Specific bacterial subsampling was indicated by enrichment of the ICLNs with Lactobacillaceae, Lachnospiraceae, Veillonellaceae, and Methanobacteriaceae and less Clostridiaceae, Pasteurellaceae, Helicobacteraceae, and Enterobacteriaceae compared to that of the mucosa. LA treatment of cereals reduced proteolytic taxa in the lumen, including pathobionts like Helicobacteraceae, Campylobacteraceae, and Fusobacteriaceae When combined, phytase- and LA-treated cereals largely increased species richness, while the single treatments reduced Actinobacteria and Bacteroidetes in ICLNs and increased mucosal MUC2 expression. In contrast, phytase reduced mucosal CDH1 expression, indicating altered barrier function with potential effects on bacterial translocation. Overall, both treatments, although often differently, changed the viable microbiome along the digesta-mucosa-lymph node axis in the ileum, probably due to altered substrate availability and microbial-host interactions.IMPORTANCE A host's diet largely determines the gut microbial composition and therefore may influence bacterial translocation into ICLNs. Due to its importance for cell metabolism, the intestinal phosphorus availability, which was modified here by phytase and LA treatment of cereals, affects the intestinal microbiota. Previous studies mainly focused on bacteria in the lumen. The novelty of this work resides mainly in that we report diet-microbe effects along the digesta-mucosa-ICLN axis and linked those effects to mucosal expression of barrier function genes as crucial components for host health. Lymph nodes can serve as reservoir of pathobionts; therefore, present diet-microbiome-host interactions have implications for food safety.