Proteorhodopsin containing prokaryotes are a class of photoherotrophic microorganisms that use a relatively simple system to harvest energy from light. This system is composed of a trans-membrane protein called proteorhodopsin (PR) and to the cofactor retinal. When exposed to light, PR changes its conformation and moves a proton from the cytoplasm side to the region between the cellular membrane and the cell wall then changes back to its original conformation. The overall goal of the project is to gain significant insights into the role of marine proteorhodopsin containing prokaryotes in the ocean by identification of PR lineages over one year.