Hydrogen isotopes in individual amino acids reflect differentiated pools of hydrogen from food and water in Escherichia coli

Abstract

Hydrogen isotope δ2 H) analysis is widely used in animal ecology to study continental-scale movement because δ2 H can trace precipitation and climate. To understand the biochemical underpinnings of how hydrogen is incorporated into biomolecules, we measured the δ2 H of individual amino acids (AAs) in Escherichia coli cultured in glucose-based or complex tryptone-based media in waters with δ2 H values ranging from -55‰ to +1,070‰. The δ2 H values of AAs in tryptone spanned a range of ∼250‰. InE. coli grown on glucose, the range of δ2 H among AAs was nearly 200‰. The relative distributions of δ2 H of AAs were upheld in cultures grown in enriched waters. In E. coli grown on tryptone, theδ2 H of nonessential AAs varied linearly with the δ2 H of media water, whereasδ2 H of essential AAs was nearly identical to δ2 H in diet. Model calculations determined that as much as 46% of hydrogen in some nonessential AAs originated from water, whereas no more than 12% of hydrogen in essential AAs originated from water. These findings demonstrate that δ2 H can route directly at the molecular level. We conclude that the patterns and distributions in δ2 H of AAs are determined through biosynthetic reactions, suggesting that δ2 H could become a new biosignature for studying novel microbial pathways. Our results also show thatδ2 H of AAs in an organism's tissues provides a dual tracer for food and environmental (e.g., drinking) water.