1 Soehngen Institute of Anaerobic Microbiology, Netherlands; Laboratory of Microbiology, Wageningen University, Netherlands. Electronic address: irene.sanchezandrea@wur.nl.
2 Soehngen Institute of Anaerobic Microbiology, Netherlands; Department of Microbiology, Radboud University, Nijmegen, Netherlands. Electronic address: mike.jetten@ru.nl.