1 Research Group of Microbiology, Department of Bioengineering Sciences, Vrije Universiteit Brussel, Pleinlaan 2, B-1050, Brussels, Belgium. Electronic address: Eveline.Peeters@vub.be.
2 Centre for Synthetic Biology, Department of Biotechnology, Ghent University, Coupure Links 653, B-9000, Ghent, Belgium. Electronic address: marjan.demey@ugent.be.