Dietary cultured supernatant mixture of Cetobacterium somerae and Lactococcus lactis improved liver and gut health, and gut microbiota homeostasis of zebrafish fed with high-fat diet.

Postbiotics have the ability to improve host metabolic disorders and immunity. In order to explore whether the postbiotics SWFC (cultured supernatant mixture of Cetobacterium somerae and Lactococcus lactis) repaired the adverse effects caused by feeding of high-fat diet (HFD), zebrafish were selected as the experimental animal and fed for 6 weeks, with dietary HFD as the control group, and HFD containing 0.3 g/kg and 0.4 g/kg SWFC as the treatment groups. The results indicated that addition of SWFC in the diet at a level of 0.3 and 0.4 g/kg didn't affect the growth performance of zebrafish (P > 0.05). Supplementation of dietary SWFC0.3 relieved lipid metabolism disorders through significant increasing in the expression of pparα and cpt1, and decreasing the expression of cebpα, pparγ, acc1 and dgat-2 genes (P < 0.05). Moreover, the content of triacylglycerol was markedly lower in the liver of zebrafish grouped under SWFC0.3 (P < 0.05). Dietary SWFC0.3 also improved the antioxidant capacity via increasing the expression level of ho-1, sod and gstr genes, and significant inducing malondialdehyde content in the liver of zebrafish (P < 0.05). Besides, dietary SWFC0.3 also notably improved the expression level of lysozyme, c3a, defbl1 and defbl2 (P < 0.05). The expression level of pro-inflammatory factors (nf-κb, tnf-α, and il-1β) were significantly decreased and the expression level of anti-inflammatory factor (il-10) was markedly increased in the postbiotics 0.3 g/kg group (P < 0.05). Feeding with SWFC0.3 supplemented diet for 6 weeks improved the homeostasis of gut microbiota and increased the survival rate of zebrafish after challenged with Aeromonus veronii Hm091 (P < 0.01). It was worth noting that the positive effect of dietary SWFC at a level of 0.3  g/kg was considerably better than that of 0.4 g/kg. This may imply that the effectiveness and use of postbiotics is limited by dosage.