Table 1. List of strains used in this study.

Strain	Description	Source
Octadecabacter arcticus 238	Type strain of O. arcticus	CRBIP, Paris, France
Octadecabacter antarcticus 307	Type strain of O. antarcticus	CRBIP, Paris, France
Gloeobacter violaceus PCC 7421	Type strain of G. violaceus	CRBIP, Paris, France
pBAD_EBAC31A08 in E. coli UT5600	Opsin gene of EBAC31A08 subcloned into expression vector pBAD in host E. coli UT5600	DeLong, E.F., MIT, Cambridge, MA, USA
pET24D_protRho2 in E. coli C43	Opsin insert of pBAD_EBAC31A08 subcloned into expression vector pET24D in host E. coli C43	This study
pET24D_oarRho2 in E. coli C43	Opsin gene of O. arcticus 238 cloned in expression vector pET24D in host E. coli C43	This study
pET24D_oanRho2 in E. coli C43	Opsin gene of O. antarcticus cloned in expression vector pET24D in host E. coli C43	This study
pET24D_gviolRho2 in E. coli C43	Opsin gene of G. violaceus PCC 7421 in expression vector pET24D in host E. coli C43	This study
pET24D in E. coli C43	Expression vector pET24D in host E. coli C43	This study