A novel extracellular mannan from Bacillus velezensis ameliorates metabolic-associated fatty liver disease by modulating gut microbiota in mice model.

Metabolic associated fatty liver disease (MAFLD) is a globally recognized chronic metabolic disorder characterized by lipid metabolism abnormalities. Accumulating evidence indicates that exopolysaccharides (EPS) could modulate the gut microbiota structure and function to prevent and treat MAFLD. Herein, a novel EPS designated BVP1 was isolated from Bacillus velezensis CGMCC 24752. Structural analysis revealed that BVP1 is a neutral α-mannan consisting of a backbone of 1,2,6-linked α-D-Manp, with branches composed of T-linked α-D-Manp, 1,2-linked α-D-Manp, and 1,3-linked α-D-Manp. Animal experiments showed that BVP1 significantly alleviated hepatic steatosis, liver injury and inflammation, and enhanced antioxidant activity in MAFLD mice. Single-nucleus RNA sequencing analysis revealed that BVP1 could restore HFD-induced imbalances in liver sinusoidal endothelial cells, hepatic stellate cells, macrophages and Kupffer cells by upregulating the expression of the lipid degradation gene Cps1 and downregulating the expression of the lipid synthesis gene Acsl1 in these cell subpopulations. Interestingly, BVP1 reshaped the gut microbiota and fecal metabolite profile by enriching beneficial bacteria and associated metabolites including salicylic acid, spermidine, and 4-hydroxyphenyl acetate. Fecal microbiota transplantation experiments verified that the anti-MAFLD effects are mediated by the BVP1-modified gut microbiota. Our findings highlight the potential of BVP1 as a promising therapeutic agent for MAFLD treatment.