Amino acids play an important role in ecology as essential nutrients for animals and as currencies in symbiotic associations. Here we present a new approach to tracing the origins of amino acids by identifying unique patterns of carbon isotope signatures generated by amino acid synthesis in plants, fungi, and bacteria ("13C fingerprints"). We measured amino acid delta 13C from 10 C3 plants, 13 fungi, and 10 bacteria collected and isolated from a boreal forest in interior Alaska, USA, using gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Microorganisms were cultured under amino-acid-free conditions and identified based on DNA sequences. Bacteria, fungi, and plants generated consistent, unique 13C fingerprints based on the more complex amino acids (five or more biosynthetic steps) that are classified as essential for animals. Linear discriminant analysis classified all samples correctly with >99% certainty and correctly classified nearly all insect samples from a previous study by diet. Our results suggest that 13C fingerprints of amino acids could provide a powerful in situ assay of the biosynthetic sources of amino acids and a potential new tool for understanding nutritional linkages in food webs.

Organic matter decomposition in the globally widespread coniferous forests has an important role in the carbon cycle, and cellulose decomposition is especially important in this respect because cellulose is the most abundant polysaccharide in plant litter. Cellulose decomposition was 10 times faster in the fungi-dominated litter of Picea abies forest than in the bacteria-dominated soil. In the soil, the added (13)C-labelled cellulose was the main source of microbial respiration and was preferentially accumulated in the fungal biomass and cellulose induced fungal proliferation. In contrast, in the litter, bacterial biomass showed higher labelling after (13)C-cellulose addition and bacterial biomass increased. While 80% of the total community was represented by 104-106 bacterial and 33-59 fungal operational taxonomic units (OTUs), 80% of the cellulolytic communities of bacteria and fungi were only composed of 8-18 highly abundant OTUs. Both the total and (13)C-labelled communities differed substantially between the litter and soil. Cellulolytic bacteria in the acidic topsoil included Betaproteobacteria, Bacteroidetes and Acidobacteria, whereas these typically found in neutral soils were absent. Most fungal cellulose decomposers belonged to Ascomycota; cellulolytic Basidiomycota were mainly represented by the yeasts Trichosporon and Cryptococcus. Several bacteria and fungi demonstrated here to derive their carbon from cellulose were previously not recognized as cellulolytic.

Groundwater within Area 3 of the U.S. Department of Energy (DOE) Environmental Remediation Sciences Program (ERSP) Field Research Center at Oak Ridge, TN (ORFRC) contains up to 135 microM uranium as U(VI). Through a series of experiments at a pilot scale test facility, we explored the lower limits of groundwater U(VI) that can be achieved by in-situ biostimulation and the effects of dissolved oxygen on immobilized uranium. Weekly 2 day additions of ethanol over a 2-year period stimulated growth of denitrifying, Fe(III)-reducing, and sulfate-reducing bacteria, and immobilization of uranium as U(IV), with dissolved uranium concentrations decreasing to low levels. Following sulfite addition to remove dissolved oxygen, aqueous U(VI) concentrations fell below the U.S. Environmental Protection Agengy maximum contaminant limit (MCL) for drinking water (< 30/microg L(-1) or 0.126 microM). Under anaerobic conditions, these low concentrations were stable, even in the absence of added ethanol. However, when sulfite additions stopped, and dissolved oxygen (4.0-5.5 mg L(-1)) entered the injection well, spatially variable changes in aqueous U(VI) occurred over a 60 day period, with concentrations increasing rapidly from < 0.13 to 2.0 microM at a multilevel sampling (MLS) well located close to the injection well, but changing little at an MLS well located further away. Resumption of ethanol addition restored reduction of Fe(III), sulfate, and U(VI) within 36 h. After 2 years of ethanol addition, X-ray absorption near-edge structure spectroscopy (XANES) analyses indicated that U(IV) comprised 60-80% of the total uranium in sediment samples. Atthe completion of the project (day 1260), U concentrations in MLS wells were less than 0.1 microM. The microbial community at MLS wells with low U(VI) contained bacteria that are known to reduce uranium, including Desulfovibrio spp. and Geobacter spp., in both sediment and groundwater. The dominant Fe(III)-reducing species were Geothrix spp.