期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：49
页码：15119-15124
DOI：10.1073/pnas.1508782112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceWe report evidence that microbes are trophically equivalent to animals. When bacteria or fungi are fed the same diets as animals, the microbes register the same trophic position as animals. This discovery reframes how microbes can be viewed within food chains and facilitates the inclusion of the microbiome in functional diversity studies. To demonstrate the broad applicability of our approach, we investigated the ancient symbioses represented by leaf-cutter ant fungus gardens, revealing four discrete trophic levels within this community and providing evidence that fungi, not ants, are the dominant herbivores of the Neotropics. Altogether, we show that microbes can be integrated with plants and animals in a food chain, thereby unifying the macro- and microbiome in studies of trophic ecology. In most ecosystems, microbes are the dominant consumers, commandeering much of the heterotrophic biomass circulating through food webs. Characterizing functional diversity within the microbiome, therefore, is critical to understanding ecosystem functioning, particularly in an era of global biodiversity loss. Using isotopic fingerprinting, we investigated the trophic positions of a broad diversity of heterotrophic organisms. Specifically, we examined the naturally occurring stable isotopes of nitrogen (15N:14N) within amino acids extracted from proteobacteria, actinomycetes, ascomycetes, and basidiomycetes, as well as from vertebrate and invertebrate macrofauna (crustaceans, fish, insects, and mammals). Here, we report that patterns of intertrophic 15N-discrimination were remarkably similar among bacteria, fungi, and animals, which permitted unambiguous measurement of consumer trophic position, independent of phylogeny or ecosystem type. The observed similarities among bacterial, fungal, and animal consumers suggest that within a trophic hierarchy, microbiota are equivalent to, and can be interdigitated with, macrobiota. To further test the universality of this finding, we examined Neotropical fungus gardens, communities in which bacteria, fungi, and animals are entwined in an ancient, quadripartite symbiosis. We reveal that this symbiosis is a discrete four-level food chain, wherein bacteria function as the apex carnivores, animals and fungi are meso-consumers, and the sole herbivores are fungi. Together, our findings demonstrate that bacteria, fungi, and animals can be integrated within a food chain, effectively uniting the macro- and microbiome in food web ecology and facilitating greater inclusion of the microbiome in studies of functional diversity.
关键词：compound specific ; food chain ; leaf-cutter ant ; microbe ; stable isotope
