Clostridium difficile has two parallel and essential Sec secretion systems.

Fagan RP, Fairweather NF
J Biol Chem. 2011 Aug 5;286(31):27483-93. doi: 10.1074/jbc.M111.263889. Epub 2011 Jun 9. (Link opens in a new window) PubMed (Link opens in a new window) Article

Plasmids from Article

ID	Plasmid	Purpose
106367	pRPF185	C. difficile inducible expression system. Shuttle plasmid containing a tetracycline-inducible gusA
106372	pRPF144	C. difficile constitutive expression system. Shuttle plasmid containing constitutive Pcwp2 -gusA