. Author manuscript; available in PMC: 2016 Sep 27.
Published in final edited form as: Mol Microbiol. 2016 Jun 1;101(4):559–574. doi: 10.1111/mmi.13408
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.