Lactulose differently modulates the composition of luminal and mucosal microbiota in C57BL/6J mice

Scope: Lactulose, one of the most studied prebiotics, displays beneficial health properties by modulation of gut microbiota. Previous studies have mainly investigated several groups of bacteria, such as bifidobacteria, lactobacilli and clostridia, in fecal samples, and there are few reports on the global and detailed effects of lactulose on luminal and mucosal microbiota. Methods and results: In this study, C57BL/6J mice were fed semi-elemental diets supplemented with lactulose at different proportions (0%, 5% and 15%) for 2 weeks. Contents and mucus of cecum and colon (equally divided into proximal, middle and distal colon) were collected and investigated. After lactulose treatment (15%), total weight and wall weight of cecum were significantly increased (P<0.05) and pH of luminal contents was dropped from 6.90~7.72 to 5.95~6.21 from cecum to the distal colon (P<0.05). The amount of total short chain fatty acids (SCFAs) in cecum and concentration of SCFAs in the middle colon were both significantly increased (P<0.05). In the control group (lactulose, 0%), the content was mostly dominanted by Firmicutes, Bacteroidetes, and Actinobacteria, while the mucus was dominanted by Firmicutes, Bacteroidetes, and Proteobacteria. After lactulose treatment (15%), the abundance of Actinobacteria and Verrucomicrobia was significantly increased (P<0.05) in the content and Proteobacteria became the most abundant phylum (54%~86%) in the mucus, especially in the distal colon. At the genus level, Bifidobacterium, belonging to Actinobacteria, and Akkermansia, belonging to Verrucomicrobia, were both significantly increased (P<0.05) in the content, and Helicobacter, belonging to Proteobacteria, became the most abundant genus in the mucus. Conclusions: Mucosal microbiota responded differently from luminal microbiota to lactulose treatment and this would be helpful for further research on the host-bacteria interactions.