Tingting Liu

Background: Diarrhea in suckling lambs is associated with gut microbiota dysbiosis, impaired intestinal barrier function, and enhanced inflammatory responses. However, the specific intestinal microbes and microbial metabolites linked to intestinal homeostasis in suckling lambs remain unclear. Results: In this study, diarrheic lambs showed significantly higher serum diamine oxidase (DAO) activity, D-lactate (D-LA), and pro-inflammatory cytokine levels than healthy lambs. We then compared gut microbial composition and metabolite profiles between healthy and diarrheic suckling lambs. Diarrheal lambs exhibited gut microbiota dysbiosis, characterized by an elevated Bacillota (syn. Firmicutes)/Bacteroidota (syn. Bacteroidetes) ratio, reduced abundance of beneficial commensals including Phocaeicola vulgatus and Bacteroides fragilis , and proliferation of the opportunistic pathogen Clostridium perfringens . Metabolomic analysis showed that, in diarrheic lambs, the tryptophan metabolism pathway was reduced with lower levels of indole-3-carboxaldehyde (IAld) and 5-hydroxyindole-3-acetic acid (5-HIAA) than in healthy lambs. Fecal microbiota transplantation experiments showed that transplantation of microbiota from diarrheic lambs partially recapitulated the donor-associated microbial, metabolic, and inflammatory phenotypes in recipient mice. Finally, functional validation using a dextran sulfate sodium (DSS)-induced colitis model revealed that supplementation with IAld and 5-HIAA significantly alleviated DSS-induced intestinal inflammation and barrier damage, accompanied by downregulated expression of genes related to the Tlr4-Myd88-Nfκb signaling pathway. Conclusions: Our findings indicate that the gut microbiota-derived tryptophan metabolites IAld and 5-HIAA alleviated inflammation and improved intestinal epithelial barrier function by enhancing tight junction integrity, while also reducing the expression of Tlr4/Myd88/Nfκb pathway-related inflammatory signaling molecules.

Fecal microbiota transplantation (FMT) promotes growth performance and intestinal development in yellow-feathered broilers, but whether the virome and metabolites contribute to its growth-promoting effect remains unclear. This study removed the microbiota from FMT filtrate using a 0.45 μm filter membrane, retaining the virome and metabolites to perform fecal virome transplantation (FVT), aiming to investigate its regulatory role in broiler growth. Healthy yellow-feathered broilers with high body weights (top 10% of the population) were used as FVT donors. Ninety-six 8-day-old healthy male yellow-feathered broilers (95.67 ± 3.31 g) served as FVT recipients. Recipient chickens were randomly assigned to a control group and an FVT group. The control group was gavaged with 0.5 mL of normal saline daily, while the FVT group was gavaged with 0.5 mL of FVT solution daily. Growth performance, immune and antioxidant capacity, intestinal development and related gene expression, and microbial diversity were measured. The results showed that FVT improved the feed utilization rate of broilers (the feed conversion ratio decreased by 3%; p < 0.05), significantly increased jejunal length (21%), villus height (69%), and crypt depth (84%) (p < 0.05), and regulated the jejunal barrier: insulin-like growth factor-1 (IGF-1) (2.5 times) and Mucin 2 (MUC2) (63 times) were significantly upregulated (p < 0.05). FVT increased the abundance of beneficial bacteria Lactobacillales. However, negative effects were also observed: Immunoglobulin A (IgA), Immunoglobulin G (IgG), Immunoglobulin M (IgM), Interleukin-1 beta (IL-1β), Interleukin-6 (IL-6), Tumor Necrosis Factor-alpha (TNF-α), and Interferon-gamma (IFN-γ) in broilers were significantly upregulated (p < 0.05), indicating immune system overactivation. Duodenal barrier-related genes Mucin 2 (MUC2), Occludin (OCLN), Claudin (CLDN1), and metabolism-related genes solute carrier family 5 member 1 (SLC5A1) and solute carrier family 7 member 9 (SLC7A9) were significantly downregulated (p < 0.05). The results of this trial demonstrate that, besides the microbiota, the gut virome and metabolites are also functional components contributing to the growth-promoting effect of FMT. The differential responses in the duodenum and jejunum reveal spatial heterogeneity and dual effects of FVT on the intestine. The negative effects limit the application of FMT/FVT. Identifying the primary functional components of FMT/FVT to develop safe and targeted microbial preparations is one potential solution.

Intestinal inflammation involves barrier impairment, immune hyperactivation, and oxidative stress imbalance. Bioactive polysaccharides universally alleviate inflammation via anti-inflammatory, antioxidant, and microbiota-modulating effects, yet exhibit distinct core mechanisms. Elucidating these differences is vital for targeted polysaccharide applications. This research examines distinct regulatory pathways through which diverse bioactive polysaccharides mitigate lipopolysaccharide-triggered intestinal inflammation in male Kunming (KM) mice. This experiment employed Lentinula edodes polysaccharide (LNT), Auricularia auricula polysaccharide (AAP), Cordyceps militaris polysaccharide (CMP), Lycium barbarum polysaccharide (LBP), and Brassica rapa polysaccharide (BRP). The expression levels of biomarkers associated with the TLR4 signaling pathway, oxidative stress, and intestinal barrier function were quantified, along with comprehensive gut microbiota profiling. The results showed that all five polysaccharides alleviated inflammatory responses in mice by inhibiting inflammatory cytokine release, reducing oxidative damage, and modulating gut microbiota, but their modes of action differed: LBP significantly suppressed the TLR-4/MyD88 signaling pathway and its downstream pro-inflammatory cytokine expression, thereby blocking inflammatory signal transduction and reducing oxidative damage; LNT and CMP enhanced the body’s antioxidant capacity by increasing antioxidant enzyme activities and decreasing malondialdehyde (MDA) levels; AAP and BRP enriched Akkermansia (Akk.) within the Verrucomicrobia (Ver.) phylum, upregulating tight junction protein expression to strengthen the intestinal mucosal barrier and indirectly reduce oxidative damage. This research demonstrates that different polysaccharides alleviate inflammation through multi-target synergistic mechanisms: LBP primarily inhibits inflammatory pathways; AAP and BRP focus on intestinal barrier protection and microbiota modulation; and LNT and CMP exert effects via antioxidant enzyme activation. These data support designing polysaccharide blends that leverage complementary inflammatory modulation mechanisms.