Contributions of direct incorporation from diet and microbial amino acids to protein synthesis in Nile tilapia

Abstract

Summary 1.Further advancement in the use of stable isotope analysis in animal ecology and physiology requires a better understanding of how organisms incorporate the macromolecular elements they consume into the tissues they biosynthesize. 2. Mixing models used to infer diets from isotopic data assume that assimilated macromolecules are dissembled into elements and then reassembled in animal tissues. 3. To test this assumption, we fed Nile tilapia diets with contrasting levels of protein and in which the carbon isotopic composition of protein differed from that of other macronutrients (carbohydrates and lipids). We then analysed the d13 C values of individual tilapia amino acids using compound-specific stable isotope analysis (CSIA). 4. C values of their corresponding dietary amino acid as protein intake increased. This pattern is consistent with assimilation of indispensable amino acids of microbial origin by tilapias fed low protein food. 6. Our results suggest that the assumptions of mixing models are sound in situations where omnivores consume protein-deficient diets, as the elemental constituents used to biosynthesize amino acids in tissues may be derived from various ingested macromolecules (e.g. protein, carbohydrates, or lipids) and their elemental components. In contrast, for omnivores that consume sufficient amounts of protein, macromolecular (e.g. protein) routing likely occurs and mixing model assumptions are violated. 7. Our study shows that CSIA is a novel method to quantify the contribution of symbiotic microbes to the amino acid homeostasis of animals.

Diversity of trophic niches among herbivorous fishes on a Caribbean reef (Guadeloupe, Lesser Antilles), evidenced by stable isotope and gut content analyses

“…However, mixing models could have overestimated the contribution of corals to their diet, precisely because of its high nutritional quality (Newsome et al 2011). Indeed, Newsome et al (2011) suggested that, for animals fed with moderate to high amounts of protein foods, mixing models can overestimate the contribution of dietary protein sources to diet, because the incorporation of dietary protein carbon was dependent on dietary protein content and on each amino acid's biosynthesis pathway.…”

“…Indeed, Newsome et al (2011) suggested that, for animals fed with moderate to high amounts of protein foods, mixing models can overestimate the contribution of dietary protein sources to diet, because the incorporation of dietary protein carbon was dependent on dietary protein content and on each amino acid's biosynthesis pathway. Benthic invertebrates also presented a high nutritional quality.…”

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

“…Extensive tests were performed with solid AA powders to determine whether or not hydrogen atoms were exchangeable with liquid water vapor at room temperature or steam at 100°C. We used the δ 2 H of the native AA standards to calculate the δ 2 H values and the isotopic fractionation in making the derivative, similar to the method used for determining δ 13 C values of AAs (12,13). Because a subset of the hydrogen atoms is removed during derivatization, we needed to know whether the remaining hydrogen atoms had similar δ 2 H values.…”

“…These fractionations are related to biochemical pathway in autotrophs and to a combination of biochemical pathway and direct incorporation in heterotrophs. Certain AAs (e.g., glutamate, alanine) can be synthesized by any eukaryotic organism (nonessential AAs), whereas others (e.g., valine and leucine) must originate from an animal's diet (essential AAs) or gastrointestinal microbiota (13). As an animal incorporates Significance Hydrogen isotope (δ 2 H) values of bulk tissues have become valuable tracers for studying migration and movement patterns in animals, but the biochemical mechanism for how hydrogen is incorporated into heterotrophic organisms is not well understood.…”

Microbes are trophic analogs of animals

“…In past work, this method has produced accurate TP estimates of zooplankton (18,21), fish (17), gastropods (17), amphibians (22), and insects (19,20), ranging from simple herbivores to higher-order carnivores. Although the utility of isotopic fingerprinting has been demonstrated in both aquatic (17,21,23,24) and terrestrial ecosystems (19,20), there remains an unbridged knowledge gap between the macro-and microbiome.…”