03/15/2016

Abiotic Pathway Makes Organic Nitrogen Compounds Available to Microbes and Plants

Manganese oxides found in some minerals interact with proteins to release organic nitrogen compounds into soils.

The Science

The ability of plants and microorganisms to take up organic nitrogen in the form of amino acids and peptides has received increasing attention over the last two decades, yet mechanisms for the formation of such compounds in soil environments remain poorly understood. A new study reveals that manganese oxides found in some minerals fragment proteins to produce soluble peptides that are released into the soil and could be directly taken up by microbes and plants.

The Impact

The study reveals how mineral-mediated, abiotic processes could produce small peptides that could contribute to the availability of organic nitrogen to plants and microorganisms. Understanding the mechanism by which nitrogen is made bioavailable is key to understanding nutrient cycling within terrestrial ecosystems.

Summary

Understanding patterns of protein abundance and diversity is critical for assessing soil ecosystem function. Unclear, however, is how minerals interact with proteins to affect nitrogen availability in soil environments. To address this question, a team of scientists from Oregon State University, Environmental Molecular Sciences Laboratory, and Leibniz Zentrum fÃ¼r Agrarlandschaftsforschung characterized reactions of a model protein called Gb1 with a mineral that contains manganese oxide (birnessite) and one that does not (kaolinite). They used nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopies at EMSL, a Department of Energy (DOE) scientific user facility. Their findings suggest that a mineral’s impact on a protein depends on the type of mineral present in the environment. In contrast to kaolinite, the manganese oxide-containing birnessite fragmented Gb1 to produce soluble peptides available to soil biota. The results confirm the existence of an abiotic pathway for the formation of organic nitrogen compounds for direct uptake by plants and microorganisms, highlighting the potential influence abiotic protein degradation could have on soil nitrogen turnover and bioavailability. Moreover, the study highlights NMR and EPR spectroscopies as valuable tools to observe reactions between proteins and minerals to shed light on soil ecosystem function.

Principal Investigator(s)

Markus Kleber
Oregon State University
[email protected]

Funding

This work was supported by DOE’s Office of Science, Office of Biological and Environmental Research, including support of EMSL, a DOE Office of Science user facility at Pacific Northwest National Laboratory; the William Wiley Distinguished Postdoctoral Fellowship at EMSL; and a research fellowship from the Institut fuer Bodenlandschaftsforschung, Leibniz Zentrum für Agrarlandschaftsforschung.

References

Reardon, P. N., S. S. Chacon, E. D. Walter, M. E. Bowden, N. M. Washton, and M. Kleber. 2016. “Abiotic Protein Fragmentation by Manganese Oxide: Implications for a Mechanism to Supply Soil Biota with Oligopeptides,” Environmental Science and Technology 50(7), 3486-93. DOI: 10.1021/acs.est.5b04622.