Lactobacillus plantarum Alters Gut Microbiota and Metabolites Composition to Improve High Starch Metabolism in Megalobrama amblycephala

The aim of this study was to explore the effects of adding <i>Lactobacillus plantarum</i> (LAB) to a high-starch diet on glucose and lipid metabolism, gut microbiota, and the composition of metabolites in <i>Megalobrama amblycephala</i>. This experiment was equipped with three isonitrogenous and isoenergetic feeds as control group (LW), high starch group (HW), and high starch with LAB group (HP). A total of 180 experimental fish (13.5 ± 0.5 g) were randomly divided into three treatments, and three floating cages (1 m × 1 m × 1 m) were set up for each treatment. A total of 20 fish per net were kept in an outdoor pond for 8 weeks. The results showed that both the HW and HP groups had an altered structure and a reduced diversity of gut microbiota. LAB increased the abundance of <i>Cetobacterium</i> and the ratio of Firmicutes/Bacteroidota and decreased PC (16:1/20:5) and taurochenodeoxycholic acid levels. LAB promoted the expression of genes related to the intestinal bile acid cycle (<i>fxr</i>, <i>hmgcr</i>, <i>rxr</i>, <i>shp</i> and <i>hnf4α</i>) and inhibited the expression of <i>pparβ</i> and <i>g6pase</i> (<i>p</i> < 0.05). LAB reduced the expression of genes related to transported cholesterol (<i>lxr</i> and <i>ldlr</i>) (<i>p</i> < 0.05) in the liver. In conclusion, LAB addition could regulate the gut microbiota disorders caused by high starch levels, promote cholesterol metabolism, produce bile acids, and reduce lipid deposition.