# Assessing gut microbial provisioning of essential amino acids to host in a murine model with reconstituted gut microbiomes

## TL;DR

This study examines whether gut microbes provide essential amino acids to mice, finding no evidence of microbial contributions to host tissues.

## Contribution

The study introduces a novel approach using stable isotope analysis to assess microbial essential amino acid provisioning in reconstituted gut microbiomes.

## Key findings

- Microbial essential amino acid contributions to host tissues were not detected in reconstituted gut microbiomes.
- 13C-EAA fingerprinting showed nearly identical patterns between germ-free and conventionalized mice.
- CVZ gut microbiota were dominated by Firmicutes and Bacteroidetes phyla, maintaining expected microbiome statuses.

## Abstract

Gut microbial essential amino acid (EAA) provisioning to mammalian hosts remains a critical yet poorly understood aspect of host-microbe nutritional interactions, with significant implications for human and animal health. To investigate microbial EAA contributions in mice with reconstituted gut microbiomes, we analyzed stable carbon isotopes (13C) of six EAAs across multiple organs. Germ-free (GF) mice fed a high-protein diet (18%) were compared to conventionalized (CVZ) mice fed a low-protein diet (10%) following fecal microbiota transplantation 30 days prior and a 20-day dietary intervention. We found no evidence for microbial EAA contributions to host tissues, with 13C-EAA fingerprinting revealing nearly identical patterns between GF and CVZ organs. Both groups maintained their expected microbiome statuses, with CVZ gut microbiota dominated by Firmicutes and Bacteroidetes phyla. These findings raise important questions about the functional capacities of reconstituted gut microbiomes. Future studies should investigate longer adaptation periods, varied dietary protein levels, and complementary analytical techniques to better understand the context-dependent nature of microbial EAA provisioning in mammalian hosts.