High-throughput sequencing reveals the effect of Bacillus subtilis CGMCC 1.921 on the cecal microbiota and gene expression in ileum mucosa of laying hens

This study evaluated the effects of Bacillus subtilis CGMCC 1.921 supplementation on the production performance, cecal microbiota and mucosal transcriptome of laying hens by 16s rRNA gene sequencing and RNA-seq. A total of 144 27-week-old Hy-Line Brown laying hens were allocated into two treatments, namely, a basal diet without additions (T0) and the basal diet supplemented with 1.0 x 10(8) cfu/g (T1) B. subtilis CGMCC 1.921, with six replicates of 12 birds in each for 24 weeks. The results showed that T1 significantly decreased feed: egg ratio compared with T0 (P < 0.05). Dietary supplementation with B. subtilis CGMCC 1.921 increased the Shannon index (P < 0.05) which indicated enhanced diversity of cecal microflora. An increasing trend in Observed species index (P = 0.072) was observed in hens fed with diets supplemented with B. subtilis CGMCC 1.921 that showed a higher species richness. And T1 modulated cecal microbiota by increasing the relative proportion of Alistipes, Subdoligranulum, Ruminococcaceae UCG-014, Anaerotruncus, Ruminiclostridium 5, Ruminococcaceae UCG-010, Erysipelatoclostridium, Ruminococcaceae UCG-009, Family XIII AD3011 group, Bacillus, Faecalicoccus, Firmicutes bacterium CAG822, Oxalobacter, and Dielma at genus level (P < 0.05). In addition, there was a tendency of increase in the relative abundance of Lactobacillus (P = 0.055), Anaerobiospirillum (P = 0.059) and Family XIII UCG-001 (P = 0.054), Peptococcus (P = 0.078), and Ruminococcaceae UCG-004 (P = 0.078). Moreover, heatmap analysis indicated that the abundance of Campylobacter and Clostridium sensu stricto 1 was lower than T0. A total of 942 genes were identified by differential expression analysis, among which 400 genes were upregulated and 542 genes were downregulated. Bioinformatics analysis suggested that the upregulated genes were involved in Peroxisome Proliferator Activated Receptor (PPAR) signaling pathway, starch and sucrose metabolism, glycine/serine/threonine metabolism, and galactose metabolism, which may promote nutrient absorption. This study provided novel insights into the probiotic mechanisms of B. subtilis on laying hens.