Proteorhodopsin in the ubiquitous marine bacterium SAR11

SAR11: basking in the light Proteorhodopsin genes were discovered, as DNA fragments in sea water, long before anybody knew what organisms they came from. They encode light-dependent proton pumps that are thought to have a central role in ocean ecology by supplying the energy for microbial metabolism, and now the intact proteorhodopsin system has been tracked down. It is found in SAR11, one of the most abundant organisms on the planet. SAR11, recently renamed Pelagibacter ubique, was synonymous with uncultured microbial diversity until it was first cultured in 2002. These organisms have proteorhodopsin proton pumps and have the odd (for a light-gatherer) ability to grow equally as well in the dark as in the light. SAR11 is out there in the oceans competing with the likes of cyanobacteria for a niche amongst the bacterioplankton. Now it seems that the cyanobacteria may have outside assistance. Viruses (or phages) that infect the ubiquitous cyanobacteria Prochlorococcus do more than just use their DNA to force the host to make more phage. The viral genome contains photosynthesis genes, possibly captured from cyanobacterial hosts long ago. These encode proteins that combine with host photosynthetic machinery to ensure that the host provides the phage with the energy necessary to produce phage progeny.