1. Department of Microbial Ecology; Netherlands Institute of Ecology (NIOO-KNAW); P.O. Box 50 Wageningen 6700 AB The Netherlands
2. Department of Chemistry, Biotechnology and Food Science; Norwegian University of Life Sciences; Aas Norway
3. Institute of Biology; Faculty of Science; Leiden University; Leiden The Netherlands
4. Soil Quality Group; Wageningen University; P.O. Box 9101 Wageningen 6700 HB The Netherlands