Enlightening the life sciences: the history of halobacterial and microbial rhodopsin research

The history of research on microbial rhodopsins offers a novel perspective on the history of the molecular life sciences. Events in this history play important roles in the development of fields such as general microbiology, membrane research, bioenergetics, metagenomics and, very recently, neurobiology. New concepts, techniques, methods and fields have arisen as a result of microbial rhodopsin investigations. In addition, the history of microbial rhodopsins sheds light on the dynamic connections between basic and applied science, and hypothesis-driven and data-driven approaches. The story begins with the late nineteenth century discovery of microorganisms on salted fish and leads into ecological and taxonomical studies of halobacteria in hypersaline environments. These programmes were built on by the discovery of bacteriorhodopsin in organisms that are part of what is now known as the archaeal genus Halobacterium. The transfer of techniques from bacteriorhodopsin studies to the metagenomic discovery of proteorhodopsin in 2000 further extended the field. Microbial rhodopsins have also been used as model systems to understand membrane protein structure and function, and they have become the target of technological applications such as optogenetics and nanotechnology. Analysing the connections between these historical episodes provides a rich example of how science works over longer time periods, especially with regard to the transfer of materials, methods and concepts between different research fields.