1 Department of Biotechnology, Delft University of Technology, Van der Maasweg 9, 2629HZ Delft, The Netherlands. Electronic address: r.kleerebezem@tudelft.nl.
2 Laboratory of Microbiology, Wageningen University & Research, Stippeneng 4, 6708WE Wageningen, The Netherlands. Electronic address: diana.sousa@wur.nl.