Proteorhodopsin

Abstract

The membrane‐bound protein Proteorhodopsin (PR) is a simple light‐dependent proton pump. The single gene that encodes PR was detected in 2000 on genomic fragments of heterotrophic marine bacteria. Over the following years, researchers realised that the majority of bacteria in the photic zone (where light is present) of nearly all oceanic water bodies possess this protein. The high abundance of closely related PR genes in only distantly related bacteria is very likely due to frequent lateral gene transfer. Experiments with PR‐containing pure cultures did not show uniform results on improved growth upon illumination, indicating a functional diversity that probably depends on environmental nutrient conditions. In most cases, PR will help bacteria to produce additional energy without the need of oxidising organic carbon. This energy can be used to grow better, move faster or survive longer during starvation periods. Key Concepts: Most marine bacteria in surface waters contain proteorhodopsin, a protein that is closely related to other rhodopsins of Archaea and Eukarya. Proteorhodopsin is a light‐dependent proton pump. The huge phylogenetic diversity of PRs in the environment might reflect to some degree a functional diversity as well. Environmental conditions have an impact on the function of PR for the residing bacteria. The activity of PR can result in enhanced growth, faster movement or extended starvation survival. The simplicity of the PR photosystem makes it an interesting target for biotechnological exploitation.

Bacterial, archaeal and viral‐like rhodopsins from the Red Sea

“…In oceanic surface waters, the light‐driven proton pumps proteorhodopsins (Béjà et al ., 2000; 2001) are estimated to occur in 13–70% of marine microbes (Sabehi et al ., ; Rusch et al ., ; Campbell et al ., ; Fuhrman et al ., ; Finkel et al ., ). Proteorhodopsins are also among the most highly transcribed genes in marine bacterial communities (Frias‐Lopez et al ., ; Poretsky et al ., ; Shi et al ., ; Gifford et al ., ; Varaljay et al ., ) and thus contribute significantly to oceanic phototrophy (DeLong and Béjà, ; Miyake and Stingl, ). Recently, type‐1 rhodopsin genes where also detected in giant viruses that infect unicellular aquatic eukaryotes (Yutin and Koonin, ).…”