Fungi link detrital resources and metazoan consumers through their role as decomposers. However, fungal contributions to metazoans may be misestimated in amino acid isotope studies because fungi are capable of both synthesizing amino acids (AAs) de novo and absorbing AAs from their environment. While fungi cultured in AA-free media have been used to represent fungi in studies of natural environments, fungi likely gain energetic benefits by taking up substrate AAs directly in situ. Consequently, fungi cultured on AA-free media may not be representative of the true variability of natural fungal δ13CAA profiles. Therefore, the objective of this experiment was to determine the effect of substrate AA availability on yeast δ13CAA profiles. We found that yeasts cultured in media of relatively higher AA content had different δ13CAA profiles than fungi grown in AA-free media, in part because yeasts utilized two essential AAs (Leu and Val) directly from media substrates when available in sufficient amounts. Furthermore, these differences among yeast δ13CAA profiles remained after normalization of δ13CAA values. We recommend further characterization of the variation in fungal δ13CAA profiles and the incorporation of this potential variability into interpretations of basal resource use by metazoans.
Bibliographical noteFunding Information:
The authors are grateful for the constructive feedback provided by two reviewers that helped to improve this manuscript. This study was funded by NSF MacroSystems Biology grant #1442595 to James Thorp and co‐PIs. The authors are grateful for the analytical work and assistance with methods reporting provided by Michael Polito and Hayat Bennadji at the Louisiana State University Stable Isotope Ecology Laboratory. They would also like to thank Ben Sikes for granting access to lab space and materials at the Kansas Biological Survey.
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