# Protocol for determining gut microbiota metabolites as substrates in mouse metabolism

## TL;DR

This paper introduces a method to study how gut microbes contribute to mouse metabolism using isotope tracing.

## Contribution

A novel protocol integrating bacterial culture and mouse experiments to trace microbiota-derived substrates.

## Key findings

- The protocol enables tracking of microbiota-derived substrates in host metabolism.
- It compares germ-free and colonized mice to assess microbial metabolic contributions.
- Stable isotope tracing links bacterial metabolism to host metabolic flux.

## Abstract

Here, we present a protocol for studying how microbiota-derived substrates fuel host mouse metabolism using stable isotope tracing. We describe steps for integrating 13C tracing in bacterial culture with 13C-labeled CO2 tracing in free-moving mice. We then detail procedures for determining the metabolic flux and fate of gut microbiota-derived substrates in the host through comparison between germ-free mice and monocolonized or specific pathogen-free mice. This protocol provides a framework for determining metabolic interactions between the gut microbiota and host.

For complete details on the use and execution of this protocol, please refer to Fang et al.1

•Steps for setting up a stable isotope gas analyzer in free-moving mice•Instructions for substrate administration and 13CO2 measurement in expired breath•Guidance on data analysis integrating 13C tracing in culture and mice

Steps for setting up a stable isotope gas analyzer in free-moving mice

Instructions for substrate administration and 13CO2 measurement in expired breath

Guidance on data analysis integrating 13C tracing in culture and mice

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Here, we present a protocol for studying how microbiota-derived substrates fuel host mouse metabolism using stable isotope tracing. We describe steps for integrating 13C tracing in bacterial culture with 13C-labeled CO2 tracing in free-moving mice. We then detail procedures for determining the metabolic flux and fate of gut microbiota-derived substrates in the host through comparison between germ-free mice and monocolonized or specific pathogen-free mice. This protocol provides a framework for determining metabolic interactions between the gut microbiota and host.