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

Abstract

Hydrogen isotope (δ 2 H) analysis is widely used in animal ecology to study continental-scale movement because δ 2 H can trace precipitation and climate. To understand the biochemical underpinnings of how hydrogen is incorporated into biomolecules, we measured the δ 2 H of individual amino acids (AAs) in Escherichia coli cultured in glucose-based or complex tryptone-based media in waters with δ 2 H values ranging from −55‰ to +1,070‰. The δ 2 H values of AAs in tryptone spanned a range of ∼250‰. In E. coli grown on glucose, the range of δ 2 H among AAs was nearly 200‰. The relative distributions of δ 2 H of AAs were upheld in cultures grown in enriched waters. In E. coli grown on tryptone, the δ 2 H of nonessential AAs varied linearly with the δ 2 H of media water, whereas δ 2 H of essential AAs was nearly identical to δ 2 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 δ 2 H can route directly at the molecular level. We conclude that the patterns and distributions in δ 2 H of AAs are determined through biosynthetic reactions, suggesting that δ 2 H could become a new biosignature for studying novel microbial pathways. Our results also show that δ 2 H of AAs in an organism's tissues provides a dual tracer for food and environmental (e.g., drinking) water.hydrogen isotopes | aminio acids | diet | Escherichia coli

Assimilation and isotopic discrimination of hydrogen in tilapia: implications for studying animal diet with δ2H

“…The large majority (~60–70%) of the hydrogen in the tissues of both terrestrial and aquatic animals is sourced from diet, not pre‐formed water; a similar pattern was also recently reported for Escherichia coli (Fogel et al. ). Similarities in the proportion of hydrogen sourced from food vs. water among animals inhabiting aquatic and terrestrial environments suggest the biochemical pathways that regulate hydrogen assimilation and incorporation into tissues are conserved among distantly related taxa.…”

“…At present, the mechanism for tissue‐specific δ 2 H discrimination is unknown, but differences in amino acid composition among tissues coupled with recent evidence that δ 2 H among individual amino acids can vary by >250‰ (Fogel et al. ) could easily create the observed patterns in tissue‐specific discrimination.…”

Diet tracing in ecology: Method comparison and selection

“…Compound‐specific stable isotope analyses of amino acids is almost exclusively performed with carbon and nitrogen isotope ratios, although in principle other stable isotope values (e.g. hydrogen) can also be obtained from amino acids (Fogel, Griffin, & Newsome, ). The carbon isotope composition of amino acids, and particularly essential amino acids, which show little isotope change during trophic transfer (McMahon, Fogel, Elsdon, & Thorrold, ), can separate among, for example, fungi, bacteria, aquatic and terrestrial primary producers in natural ecosystems (Larsen et al., ).…”

Derivatization‐free method for compound‐specific isotope analysis of nonexchangeable hydrogen of 4‐bromophenol

“…To date, relatively few CSIA studies have reported hydrogen isotope data from compounds containing exchangeable hydrogen after derivatization of the polar functional groups, mostly from analysis of biological fatty acids, and, to a lesser extent, from analysis of amino acids . The present derivatization‐free method offers an alternative approach for this type of analysis.…”

“…Consequently, the isotope composition of the exchangeable hydrogen can vary among samples, introducing an unknown contribution into the net isotope ratio of the target compound obtained by CSIA. While derivatization can eliminate exchangeable hydrogen from the molecules subject to CSIA, few well‐documented examples of such methods have been published to date, exclusively on the analysis of long‐chain fatty acids and of amino acids …”