1. Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
3. Department of Microbiology, Radboud University Nijmegen, Nijmegen 3, Nijmegen 6525 AJ, The Netherlands
4. Institute for Geosciences, University of Kiel, Kiel D-24098, Germany