1. Institute of Microbiology, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland.
2. Institute for Chemical and Bioengineering, Department of Chemistry, ETH Zürich, 8093 Zürich, Switzerland.
3. Merck Healthcare, Biotech Process Sciences, Route de Fenil 25, 1804 Corsier-sur-Vevey, Switzerland.