CORA – Copper Acquisition


Archaea (Copyright: Christa Schleper/Universität Wien)

Project start: 2016

How archaea capture copper from soils

Ammonia oxidizing archaea play an important role in the nitrogen cycle on Earth. In order to oxidize ammonia to nitrite, the single-celled microorganisms require copper. In the course of a Marie Curie Fellowship, microbiologist Carolina Reyes examines strategies how archaea take-up copper from soils and water. The project arises from the Environmental Sciences Research Network of the University of Vienna and is based on cooperation between scientists in the fields of environmental geosciences (led by Stephan Krämer) and microbiology (led by Christa Schleper).

Archaea constitute one of the three domains of life and, together with bacteria, they are the main actors controlling nitrification as a key component in the nitrogen cycle. Nitrification describes the biological process of converting ammonia to nitrite and subsequently to nitrate. In 2005 ammonia oxidizing archaea (AOA) have been detected for the first time. Since then they have been found to be globally distributed and in large amounts in almost all terrestrial and marine environments, which raised expectations among scientists that AOA play a major role in environmental processes. 

“Ammonia oxidizing archaea require enzymes containing copper in order to convert ammonia to nitrite. To date we do not know how the microorganisms take up copper from soil and water. In our project we want to describe the molecular pathways for copper uptake”, says postdoctoral researcher Carolina Reyes from the Department of Environmental Geosciences. Her project “CORA – Copper Acquisition” is linked to the research groups of environmental geochemist Stephan Krämer (Department of Environmental Geosciences) and microbiologist Christa Schleper (Department of Ecogenomics and Systems Biology). The two research groups work intensively on environmental geochemistry of nutrient acquisition respectively the characterisation of archaea.

Searching for molecular mechanisms

What types of proteins are involved in copper uptake? How does copper uptake differ between archaea that derive from soils and archaea that have been isolated from aquatic systems? What different copper acquisition strategies exist? The project that runs for two years aims at finding answers to these questions. “We already know that in bacteria various models for copper acquisition and incorporation of copper into enzymes exist”, says Stephan Krämer, Head of the Department of Environmental Geosciences. It is currently unknown how AOA acquire copper from the environment, but the researchers have various hypotheses how this process is integrated into the metabolism of the organisms.

For their studies the researchers make use of strain Nitrososphaera viennensis, an archaeon that was described by Christa Schleper’s group a few years ago. It was isolated in 2011 from soil in the garden of the Department for Ecogenomics and Systems Biology of the University of Vienna. „Like in other AOA representatives the genome of N. viennensis shows a surprisingly high number of genes coding for copper-dependent enzymes. Therefore we expect them to have very efficient systems for copper uptake“, says Christa Schleper, Head of the Division of Archaea Biology and Ecogenomics of the Faculty of Life Sciences.

A hypothesis that will be tested in the project is whether AOA trigger changes in geochemistry in their surrounding environment in case of copper shortage. This process might involve highly specialised ligands, so called metallophores, which are able to bind to copper and to form extremely stable, soluble complexes that can be absorbed by the organisms. This mechanism could have an impact on the rate of ammonia that is converged into nitrite. The overall goal of the project is to contribute to the basic understanding of copper uptake by archaea.

Contact persons:

Prof. Stephan Krämer
Head of the Department of Environmental Geosciences
University of Vienna
1090 - Wien, Althanstraße 14 (UZA II)
+43-1-4277-534 63
+43-664-60277-534 63

Prof. Christa Schleper
Head of the Division of Archaea Biology and Ecogenomics of the Faculty of Life Sciences
University of Vienna
1090 - Wien, Althanstraße 14 (UZA I)
+43-1-4277-765 10
+43-664-60277-765 10

Project Summary

It has recently been discovered that archaea are promoting ammonia oxidation, an important process in nitrogen cycling. Ammonia oxidizing archaea (AOA) use Cu containing enzymes to oxidize ammonia to nitrite. Therefore, they have an elevated Cu requirement and thus the bioavailability of Cu to archaea may impact the nitrogen cycle. However, the molecular mechanism of Cu uptake by Archaea from terrestrial and aquatic environments remains unknown. Understanding the molecular mechanism of Cu uptake by these archaea will be an important step in understanding limitations of nitrification activities in the nitrogen cycle. The first objective of this study will be to determine what types of proteins are potentially involved in Cu uptake under Cu limiting conditions. The hypothesis that low concentrations of Cu will result in expression of Cu acquisition genes will be tested using different strains of AOA originating from soil and hot spring environments and varying the availability of Cu to the AOA. The gene expression of AOA cultures as a function of Cu availability will be monitored using transcriptome studies. The hypothesis that soil AOA will secrete extracellular reactive compounds to mobilize Cu as part of a Cu acquisition strategy will be tested. The presence of a strong copper binding ligand will be evaluated using a colorimetric assay and an electrochemical method. The second objective of this study will be to use different strains of AOA in batch incubation experiments with different previously characterized Cu containing soils and minerals. The hypothesis that AOA isolated from soil environments will have high efficiency Cu uptake systems compared to AOA from the aquatic environment will be tested in batch incubations with AOA cell cultures and different Cu containing soils and minerals. This study will help to elucidate Cu uptake of AOA and of Archaea in general and to increase our understanding of factors limiting nitrification activities in the environment.