Martinez, A., Bradley, A.S., Waldbauer, J.R., Summons, R.E. and Delong, E.F.
Notes: Photorhodopsins (PRs), retinal-binding membrane proteins that catalyze light-activated proton efflux across the cell membrane, are found in many marine bacteria. These authors screened a fosmid library of planktonic DNA, looking for PR-expressing clones. Candidate clones, identified by pigment formation on retinal-containing plates, were sequenced and subjected to transposon-mediated mutagenesis. Six genetically linked genes were identified and shown to be sufficient for the synthesis of functional PR photoprotein in E. coli. Light-induced changes in ATP levels were measured in E. coli recombinant clones expressing the PR photosystem and mutant PR- derivatives. ATP measurements performed after 5 minutes of light stimulation showed significant light-induced increases in cellular ATP levels in PR+, but not in PR- cells. The data therefore demonstrated that the E. coli clones expressing the PR genes acquired a fully functional phototrophic system that drove cellular ATP synthesis upon illumination. The BacTiter-Glo™ System was used to measure light-induced changes in ATP levels. (3581)