Gut microbial metabolism of amino acids and its impact on enteric infections.

Amino acids are the fundamental building blocks of proteins. Dietary proteins and endogenous protein turnover are the main sources of amino acids in the body. Over the past decade, our understanding of the role of the gut microbiota in amino acid metabolism has expanded considerably. The gut microbiota metabolizes dietary amino acids, regulates intestinal amino acid bioavailability, and maintains host nutrient homeostasis. Besides nutrient regulation, emerging evidence has revealed that amino acid availability in the gut also plays a crucial role in modulating enteric infections. Amino acids can influence infection outcomes both directly, by affecting the virulence of enteric pathogens, and indirectly, by shaping host immune responses. While most studies have focused on bacterial metabolism of amino acids, recent findings highlight important contributions from non-bacterial members of the gut microbiota, including fungi and protists. Both fungi and protists can shape amino acid availability in the gut and, consequently, infection outcomes. In this review, we integrate current knowledge on how diet and amino acid metabolism, mediated by both bacterial and non-bacterial communities, collectively influence enteric infection dynamics.