Disclosed herein are methods and systems for expressing a polypeptide in a Rhodospirillum species. The methods include introducing an expression vector having a nucleic acid sequence encoding the polypeptide operably linked to a puc promoter into the Rhodospirillum bacterium and growing the Rhodospirillum bacterium under conditions that allow expression of the polypeptide. Vectors for expressing a membrane polypeptide in a Rhodospirillum species are disclosed. The vectors include a puc promoter and a nucleic acid encoding a membrane polypeptide.