Seeing the Potential

neuronal signalingI had never heard of Halorubrum sodomense until a few days ago. It’s name describes it pretty well, it is a salt-tolerant (Halophilic) organism that contains the red-colored photosynthetic pigment archaerhodopsin, and it was originally isolated from the region of Sodom near the Dead Sea. It’s an organism that is well-known only to those with reason to study it. Many of the rest of us will never have cause to say its name, or to even remember it, and may even occasionally wonder why it is studied at all.

Halorubrum sodomense was in the news recently because a genetically engineered form of its rhodopsin was used to create a method that lights up mammalian neurons as they fire. This exciting development was reported in a paper by Kralj et al, published in the Nov 27 issue of Nature Methods.

The paper describes an interesting application of the pigment Halorhodopsin–a light-activated proton pump that captures solar energy. At neutral pH it exhibits red fluorescence, and high pH it does not fluoresce. The changes in pH are associated with deprotonation. The authors of the paper exploited this property to create an engineered form of halorhodopsin that fluoresces as a result of changes in membrane potential. Transfection of neuronal cells with the altered halorhodopsin led to expression of the engineered pigment in the cell membrane. This enabled visualization of the progress of an action potential as the neuron fired by monitoring the generation of red fluorescence as it travelled along the neuron. Previously it the only way to monitor electrical activity in such a cell was to insert an electrode. This the new method is less invasive, allows monitoring of changes in membrane electrical activity at more than one location in the cell, and raises the possibility of visualizing how signals spread through neuronal networks, and potentially how they propagate in living animals.

The paper is very exciting in itself, the science is elegant and the results beautiful and promising. However, to me it also illustrates another important point about scientific progress. Halorubrum sodomense is a relatively obscure organism, yet knowledge of it’s physiology was key to the method developed. It shows how no knowledge is really insignificant, and that the ability to identify and apply the right knowledge to the right problem is something that has awesome potential in every field of research.

We can probably all think of other examples where an observation or piece of knowledge from one field of study has been successfully adapted to create tools or medicines that have proven valuable in others. Around here bioluminescence springs to mind as a natural phenomenon that has been taken and adapted to create tools to advance knowledge in many areas. The discovery of penicillin is the classic example of the results of someone being observant enough to notice an effect, and then smart enough to see the application. Of course this is what science is all about, but this week the elegant application of an H. sodomense pigment to the problem of visualizing neuronal signals brought it into fresh perspective for me.

Here’s the paper:

ResearchBlogging.orgKralj JM, Douglass AD, Hochbaum DR, Maclaurin D, & Cohen AE (2011). Optical recording of action potentials in mammalian neurons using a microbial rhodopsin. Nature methods PMID: 22120467

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Isobel Maciver

Isobel Maciver

Isobel was a graduate of the University of Edinburgh and of Aston University in Birmingham, U.K. She was a technical writer and editor, and manager of the Scientific Communications group at Promega and later went on to manage web page content and publishing. Isobel's ever helpful and serving spirit, her dry Scottish humor and her kind heart will be forever missed by her Promega Connections colleagues.


  1. Ever since green fluorescent protein came on the scene, as biologist, I am so pleased and in awe of the new ways we can visualize mechanisms in the living organism. This genetically engineered rhodopsin will surely find many more uses!

    I am paying “blog calls” to each @scio12 attendee to say “Hi” and give your blog a shoutout on twitter (I’m @sciencegoddess). I look forward to meeting you in January!

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