# Metagenomics and Machine Learning Identify TMA-Producing Serratia Induced by High-Fat/Choline Diet: A Novel Obesity Target for TMA

## TL;DR

This study finds that a high-fat and choline diet increases TMA/TMAO levels via Serratia bacteria, offering a new target for obesity-related metabolic disorders.

## Contribution

Identifies Serratia marcescens as a novel TMA-producing bacterium under high-fat/choline diet conditions using metagenomics and machine learning.

## Key findings

- High-fat and choline diet synergistically increase TMA/TMAO levels, worsening metabolic disorders.
- Serratia marcescens is identified as a key TMA-producing microorganism under these dietary conditions.
- CutC enzyme in Serratia shows high choline affinity, supporting its role in TMA production.

## Abstract

Background: High-fat diet-induced metabolic disorders are associated with trimethylamine (TMA)/trimethylamine N-oxide (TMAO), whose production is linked to gut microbial choline metabolism. However, changes in specific gut microbiota under a high-fat diet and the relationship between these changes and choline in TMA/TMAO production remain unclear. Methods: A total of 48 7-week-old male C57BL/6J mice were subjected to one-week acclimatization feeding, and then randomly divided into four groups (12 mice per group) to establish a 2 × 2 factorial design animal experiment: the control group (CON, basal diet), the choline-supplemented control group (CON + C, basal diet supplemented with 1% choline), the high-fat diet group (HF, high-fat diet), and the high-fat plus choline group (HF + C, high-fat diet supplemented with 1% choline). The experiment lasted for 9 weeks, during which dynamic monitoring of TMAO levels in mice was performed in the first 4 weeks. At the ninth week, the mice were sacrificed and samples were collected for subsequent assays, including the concentrations of TMA and TMAO in serum, colonic contents and feces; the pathological morphology of liver tissue, adipocyte staining characteristics and serum biochemical parameters; and the expression levels of key genes and proteins in liver, small intestine and colon tissues. Meanwhile, metagenomic analysis was conducted on colonic contents, combined with machine learning to predict the correlation between gut microbiota and TMA. In addition, gene cloning, multiple sequence alignment, molecular simulation and in vitro culture experiments were carried out to verify the TMA-producing function of the target strain. Results: This study elucidated that high-fat diet and high choline exert a significant interaction in TMA/TMAO production through a 2 × 2 animal experiment; meanwhile, the significantly increased TMA/TMAO levels co-induced by the two factors further exacerbate metabolic disorders. Notably, through combined metagenomics and machine learning, we identified Serratia marcescens as the primary TMA-producing microorganism under high-fat/choline diet induction. In vitro cultures simulating the intestinal environment revealed that the TMA conversion ability of Serratia marcescens is time-dependent, reaching 60 ± 2.49% after 24 h of anaerobic culture with choline chloride. Multiple sequence alignment and molecular simulation further demonstrated that the CutC enzyme of Serratia marcescens has a conserved amino acid sequence and high affinity for choline. Conclusions: We uncovered a two-factor synergistic effect of a high-fat/choline diet on TMA/TMAO, and for the first time identified the genus Serratia as a TMA-producing bacterium. These findings provide a new potential target for intervening in metabolic disorders mediated by high-fat diet-induced TMAO elevation.