Swappable DNA Module in Bacteria Gives Light Harnessing Ability

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Engineering Bacteria to Harvest Light


Some bacteria, such as cyanobacteria, use photosynthesis to make sugars, just as plants do. But others have a newly discovered ability to harvest light through a different mechanism: using light-activated proteins known as proteorhodopsins, which are similar to proteins found in our retinas. When the protein is bound to a light-sensitive molecule called retinal and hit with light, it pumps positively charged protons across the cell membrane. That creates an electrical gradient that acts as a source of energy, much like the voltage, or electromotive force, supplied by batteries.

First discovered in marine organisms in 2000, scientists recently found that the genes for the proteorhodopsin system – essentially a genetic module that includes the genes that code for both the protein and the enzymes required to produce retinal – are frequently swapped among different microorganisms in the ocean.

Intrigued by the prospect that a single piece of DNA is really all an organism needs to harvest energy from light, the researchers inserted it into E. coli. They found that the microorganisms synthesized all the necessary components and assembled them in the cell membrane, using the system to generate energy.

The findings have implications for both marine ecology and for synthetic biology, an emerging field that aims to design and build new life forms that can perform useful functions. Giant genomic studies of the ocean have found that the rhodopsin system is surprisingly widespread. The fact that a single gene transfer can result in an entirely new functionality helps explain how this genetic module traveled so widely. In fact for microbes, this kind of module swapping may be the rule rather than the exception.

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3 Comments

  1. This seems like really old news to me. We have been aware of bacterial rhodopsin for at least 30 years and knew that it acts as a proton pump allowing production of ATP in the usual electron transport way.  
     
    This has been all over the news, but it seems that all they did was add one such gene to E.coli and find Ta DA!! A proton gradient. 
     
    Did I miss something?

  2. Mike, I find it interesting for two reasons: 
     
    First, a single gene coded for all the components needed to build a functional system. 
     
    Second, this ?swappable? light harvesting system is very common in the bacterial world. 
     
    To me this indicates that some bacteria genes may have evolved as independent units that have co-evolved with bacterial ?containers?. I?m thinking of modular software. The ?light harvesting? module evolved to become a single, swappable functional unit. The bacterial ?container? evolved so that it could use such swappable units. Thus the survival of the functional unit depends on all bacteria strains that can use the unit. The survival of the bacterial ?container? depends on all the swappable units that the strain can use.

  3. I’m thinking of the story possibilities here. :) 
     
    BTW, don’t assume eukaryotic cells can’t exchange genetic material. CF. Sticker’s Sarcoma and Devil Facial Tumor Disease for a possible example.

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