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Carbon 13 discrimination during lipid biosynthesis varies with dietary concentration of stable isotopes: implications for stable isotope analyses
Author(s) -
Wessels Frank J.,
Hahn Daniel A.
Publication year - 2010
Publication title -
functional ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.272
H-Index - 154
eISSN - 1365-2435
pISSN - 0269-8463
DOI - 10.1111/j.1365-2435.2010.01716.x
Subject(s) - trophic level , biology , bacillus subtilis , isotope , isotopes of carbon , stable isotope ratio , biosynthesis , δ13c , isotope analysis , heterotroph , food science , ecology , biochemistry , bacteria , enzyme , total organic carbon , genetics , physics , quantum mechanics
Summary 1. Carbon stable isotopes are commonly used as a research tool in physiological ecology. When elements are consumed, they are naturally enriched or depleted as the consumer processes them. The difference in isotopic composition between the consumer and the diet is known as the discrimination factor (Δ 13 C). 2. Mixing models are used to estimate the contribution of multiple dietary components to a consumer’s tissues and discrimination must be estimated in the model. Often, discrimination factors vary depending on multiple factors, yet in many models the discrimination factor is assumed to be constant for each dietary component. 3. Few studies have evaluated the mechanistic basis of stable isotope metabolism and discrimination during macromolecule biosynthesis, despite the potential to improve estimations of discrimination factors. We tested whether 13 C discrimination depends on the dietary concentration of 13 C by culturing the bacterium Bacillus subtilis in a gradient of broths ranging from a δ 13 C of −11·8‰ to −25·3‰. We found an increase in discrimination in whole bacterial tissue, bulk lipid, and lipid‐extracted fractions as dietary the concentration of 13 C increased, with lipids showing the greatest discrimination ranging from 2·72‰ in the low 13 C broths to 15·5‰ in the high 13 C broths. 4. These findings contrast with the majority of isotopic ecology data that typically show a moderate enrichment of 13 C as trophic level increases. This discrepancy is attributed to the de novo biosynthesis of the majority of cellular components in this study as opposed to the effects of isotopic routing seen in more metabolically complex taxa.