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

Abstract

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.

Photochemical characterization of actinorhodopsin and its functional existence in the natural host

“…Later, three relatives with different functions were discovered from the same archaeon: inward Cl -pump halorhodopsin [5], phototaxis sensors sensory rhodopsin I [6], and sensory rhodopsin II (also called phoborhodopsin) [7]. For approximately 30 years, research on microbial rhodopsins was confined to these four archaeal rhodopsins [8]. Since 1999, however, the genes for other microbial rhodopsins have been identified in various microorganisms, including eubacteria, fungi, algae, and even viruses.…”

“…The expression of photoactive PR was verified in native planktonic membrane preparations [17]. Later, PR genes were identified in other oceanic microbial groups, and it was established that PR-encoding microorganisms are common in the world oceans (for reviews, see [8,18]). The cellular expression of PR and its H + -pumping activity were also proven in cultivated host strains.…”

Characterization of a Cyanobacterial Chloride-pumping Rhodopsin and Its Conversion into a Proton Pump

“…Microbial rhodopsins were originally discovered in highly halophilic archaea in the early 1970s to 1980s (3). Since 1999 their homologues have begun to be identified in various microorganisms inhabiting a broad range of environments (4 -6).…”

Marine Bacterial and Archaeal Ion-Pumping Rhodopsins: Genetic Diversity, Physiology, and Ecology

“…The recognition of microbial rhodopsins as light-driven ion pumps began in the 1970s when Stoeckenius and Oesterhelt decided to study the colorful inhabitants of crystallizer ponds in solar salterns (9,10). The photopigment they found in Halobacterium salinarum (Archaea) they named bacteriorhodopsin (BR), and its discovery initiated a long and detailed series of structural, biochemical, and biophysical studies (see references 4 and 11 for reviews).…”