Self-organization of dissolved organic matter to micelle-like microparticles in river water

Abstract

In aquatic systems, the concept of the ‘microbial loop’ is invoked to describe the conversion of dissolved organic matter to particulate organic matter by bacteria1. This process mediates the transfer of energy and matter from dissolved organic matter to higher trophic levels, and therefore controls (together with primary production) the productivity of aquatic systems. Here we report experiments on laboratory incubations of sterile filtered river water in which we find that up to 25% of the dissolved organic carbon (DOC) aggregates abiotically to particles of diameter 0.4–0.8 micrometres, at rates similar to bacterial growth. Diffusion drives aggregation of low- to high-molecular-mass DOC and further to larger micelle-like microparticles. The chemical composition of these microparticles suggests their potential use as food by planktonic bacterivores. This pathway is apparent from differences in the stable carbon isotope compositions of picoplankton and the microparticles. A large fraction of dissolved organic matter might therefore be channelled through microparticles directly to higher trophic levels—bypassing the microbial loop—suggesting that current concepts of carbon conversion in aquatic systems require revision.

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Figure 1: Changes in organic matter size speciation and associated δ13C values during abiotic incubation of sterile filtered and poisoned Elbe water.
Figure 2: Total reflection X-ray fluorescence difference and proton NMR spectra of microparticles produced during abiotic incubation.
Figure 3: Transmission electron microscopy of aggregated DOM.
Figure 4: Diagram of DOM transformation in the microbial loop bypassed (dashed lines) by abiotic microparticle formation.

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Acknowledgements

We thank L. Ehrhardt for technical assistance and H. Lother for discussions. This research was funded by the Deutsche Forschungsgemeinschaft (M.K. and A.S). The Heinrich-Pette-Institute is supported by the Bundesministerium für Gesundheit and the Freie und Hansestadt Hamburg.

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Correspondence to Martin Kerner.

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Kerner, M., Hohenberg, H., Ertl, S. et al. Self-organization of dissolved organic matter to micelle-like microparticles in river water. Nature 422, 150–154 (2003). https://doi.org/10.1038/nature01469

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