Clostridium Species as Metallic Copper-Forming Bacteria in Soil under Reducing Conditions

Abstract

Recent studies have reported the formation of Cu⁰ nanoparticles (CuNP) by suspended bacteria in pore water of periodically flooded soils, but the bacteria have not yet been identified. The aim of this study was to identify the CuNP-forming bacteria and to determine the location of CuNP formation relative to the bacterial cell surface. Electron microscopy revealed that the bacteria were rod-shaped spore formers and suggested that CuNP were formed in the periplasm. Combined results from denaturing gradient gel electrophoresis, 16S rRNA gene clone libraries, and classic microbiological cultivation techniques provided strong evidence for a Clostridium sp. strain as the CuNP-forming bacteria. Clostridia are well-adapted to frequent flooding and drying due to their ability to form spores and may play an important role in Cu cycling and metallic Cu formation in redox-dynamic environments.

Keywords:

• biomineralization
• Clostridia
• copA
• copper
• metals
• nanoparticles
• molecular microbial ecology
• redox
• soil
• spore forming bacteria
• wetland

Acknowledgments

Karin Stögerer is acknowledged for her help with microbiological analyses and for performing parts of the molecular microbiology work. Kurt Barmettler is acknowledged for his support in the Soil Chemistry Laboratory at ETH. We thank the electron microscopy center at ETH Zurich (EMEZ) for providing TEM facilities and Philippe Gasser for his assistance at the SEM. Fabian Gramm is acknowledged for the red cyan anaglyph images taken at CM12 at EMEZ.

Funding

This research benefitted from an exchange grant within the ESF Research Networking Program FIMIN, which is gratefully acknowledged. The study was financially supported by ETH Zurich, Eawag and University of Tübingen.

Supplemental Material

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