Lactiplantibacillus plantarum Lp20 Alleviates High Fat Diet-Induced Obesity in Mice via Its Bile Salt Hydrolase Activity

<b>Background:</b> Obesity is a highly prevalent chronic disease characterized by excessive weight gain and fat accumulation. There is growing evidence that <i>Lactiplantibacillus plantarum</i> strains with bile salt hydrolase (BSH) activity are effective in preventing and alleviating obesity. <b>Methods:</b> Initially, we screened bacterial strains with high hydrolytic activity against glycochenodeoxycholic acid (GDCA), and constructed an isogenic bsh1 knockout mutant. Subsequently, male C57BL/6J mice fed a high-fat diet (HFD) were randomly assigned to receive daily gavage of either the wild-type Lp20 (Lp20-WT) or the bsh1-deficient mutant (Lp20-<i>Δbsh1</i>) for 8 weeks. Serum cholesterol levels and histopathological changes in liver sections were monitored. Hepatic gene expression was quantified by RT-qPCR, and fecal bacterial communities were analyzed via 16S rRNA gene sequencing. These comprehensive assessments aimed to evaluate metabolic improvements and uncover the potential mechanisms behind the observed effects. <b>Results:</b><i>L. plantarum</i> Lp20 hydrolyzed 91.62% of GDCA, exhibiting the highest bile-salt hydrolase (BSH) activity among tested isolates. Whole-genome sequencing and in-silico analyses mapped this activity to <i>bsh1</i>; gene deletion of <i>bsh1</i> confirmed the role of <i>bsh1</i> in GDCA hydrolysis. Daily gavage of the wild-type strain (Lp20-WT) to diet-induced obese mice markedly attenuated weight gain, reduced inguinal white adipose tissue and mesenteric fat mass, and lowered serum TC and LDL-C by 20.8% and 33.3%, respectively, while decreasing ALT and AST levels and reversing hepatic steatosis. In contrast, the bsh1-null mutant (Lp20-<i>Δbsh1</i>) failed to elicit any measurable metabolic benefit. Mechanistically, Lp20-WT upregulated rate-limiting bile-acid synthetic enzymes CYP7A1 and CYP27A1, thereby accelerating the catabolism of cholesterol into bile acids. Concurrently, it activated hepatic TGR5 and FXR signaling axes to modulate hepatic metabolism. Moreover, Lp20-WT restructured the gut microbiota by notably enhancing the abundance of beneficial bacteria such as <i>norank_f__Muribaculaceae</i>, <i>Akkermansia</i>, and <i>Alistipes</i>, while reducing the abundance of potentially harmful taxa, including <i>norank_f__Desulfovibrionaceae</i>, <i>Dubosiella</i>, and <i>Mucispirillum</i>. <b>Conclusions:</b> This study provides direct evidence of BSH's anti-obesity effects through gene deletion. Specifically, BSH lowers cholesterol by modulating hepatic bile-acid metabolism-related gene expression and altering the gut microbiota composition. However, the study is limited by a small sample size (<i>n</i> = 6), the use of male mice only, and its preclinical stage, indicating a need for further validation across diverse strains and human populations.