Fig. 5

The product of BG degradation by B. uniformis promotes the proliferation of L. johnsonii. A–K B. uniformis degraded BG and promoted the proliferation of L. johnsonii. For bacteria-related experiments, n = 3 per group; for animal-related experiments, n = 6 per group. A Growth curves of L. johnsonii in basal medium (without carbon source) containing BG or glucose as the sole carbon source. B Gut microbial co-occurrence network analysis based on core genus and species (average relative abundance > 0.1%) in the feces of mice (BG and vehicle groups). The red line indicates Spearman rank correlation coefficient > 0.30 and FDR-adjusted P < 0.05; the blue line indicates Spearman rank correlation coefficient <  − 0.30 and FDR-adjusted P < 0.05. C Spearman correlation between abundances of B. uniformis with L. johnsonii in feces of mice (BG + DSS and DSS groups). D Growth curves of B. uniformis in basal medium (BG or glucose as the sole carbon source). E The abundance of L. johnsonii after the co-culture of B. uniformis and L. johnsonii in the basal medium (BG as the sole carbon source) for 48 h. F Schematic of potential interaction between B. uniformis (BU) and L. johnsonii (LJ) via fermented products/metabolites. Briefly, BU was grown in basal medium (BG as the sole carbon source) for 48 h, followed by centrifugation of 4720 × g for 20 min at 4 °C. The supernatant was adjusted to pH 6.8 and sterilized by filtration (0.22 μm pore size) for inoculation of LJ. G Growth curves of L. johnsonii in basal medium (BG as the sole carbon source) with or without B. uniformis pre-culture for 24 h. H Metabolites profile in the supernatant at different time points. The purple lines indicate the metabolites that are increased during the growth of B. uniformis and decreased during the growth of L. johnsonii. I A heat map of the top 10 metabolites (based on the fold change value of LJ-24h/BU-48h) detected by untargeted metabolomics. J T-statistic of all detected metabolites by untargeted metabolomics. K Growth curve of L. johnsonii under the stimulation with different concentrations of NAM. L Experimental schema for M–U. Mice were treated with 100 mg/kg of NAM or PBS daily for 14 days, and 3% (w/v) DSS was added to the drinking water from day 7 to day 14. n = 6 mice per group. M, N Body weight (M) and disease activity index (N) were monitored daily after DSS treatment. O Representative photographs (left) and length quantification (right) of colon tissues. P Representative H&E-stained sections (upper) and AB/PAS-stained sections (lower) of the distal colon tissue. Scale bars, 100 μm. Q Histology score (left) was determined from H&E-stained sections, and the number of goblet cells per crypt (right) was determined from AB/PAS-stained sections. R The abundance of L. johnsonii in vehicle- and NAM-treated mice. S Relative gene expression of Cyp1a1 and Il22 in colon tissue assessed by RT-qPCR. T Colonic levels of IL-22. U Representative Muc2-stained colon sections (left) and quantified Muc2-positive area (right). Scale bars, 50 μm. Data are presented as the mean ± SEM. Statistical analysis was performed using t-test for E and O–U and two-way ANOVA followed by Bonferroni’s post hoc test for K–N