Soil microorganisms are the primary mediators of organic matter decomposition and humification processes in soil, which represent a critical C flux in the global C cycle. Little is known about how soil microbes regulate carbon cycling including the contribution of their own biomass to stable soil organic matter. A comprehensive understanding of microbial composition is a first step to unraveling microbial regulation of soil humification processes. For this purpose, we isolated 23 microbial strains representing four major groups (Gram (+) bacteria, Gram (-) bacteria, Actinobacteria, and Fungi) from a temperate and a tropical forest soil. The microbial isolates were cultured with uniformly 13C-labeled glucose as the C source such that all biochemical components synthesized from glucose were 13C labeled. This approach enabled field mesocosm experiments on tracking microbial decomposition, while facilitating solution- and solid-state NMR analysis of microbial composition. Polar and lipid extracts of labeled biomass of the four microbial groups from the two forest sites were profiled by 2D NMR methods, including high-resolution heteronuclear single quantum coherence spectroscopy and HCCH-total correlation spectroscopy. This 13C labeling approach also enabled the analysis of intact biomass by 2D solid-state 13C- 13C correlation spectroscopy. Distinction between microbial groups and sites was observed in the polar and lipophilic metabolite profiles. Dominant differences could also be related to the capacity for lipid β-oxidation or adaptation to desiccation. Solid-state NMR further revealed differential synthetic capacity for glycolipids among groups. This technology coupled with 13C metabolite profiling should facilitate future functional annotation of indigenous microbial genomes.
|Number of pages||15|
|State||Published - 2009|
Bibliographical noteFunding Information:
Acknowledgments This work was supported by NSF grants DEB0343577 and EPS-0447479. NMR spectra were recorded at the J.G. Brown Cancer Center NMR facility. Part of this work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Berkeley National Laboratory, under contract DE-AC02-05CH11231. We thank T. Shimada, E. Long and J. Fortney for their assistance with the microbial isolation, screening and culture of the microorganisms; and S. Arumugam for help with solid state NMR. We also thank Drs. Mary Firestone and Richard Higashi for helpful discussion.
- 2D solid-state C NMR
- 2D solution-state NMR
- Gram negative bacteria
- Gram positive bacteria
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Clinical Biochemistry