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Researchers Sequence Genome of Photosynthetic Bacterium That Uses Near-Infrared Light

5 February 2008

Acaryo
Photomicrograph of Acaryochloris marina. Source: Phototrophic Prokaryotes Sequencing Project

Researchers at Washington University in St. Louis and Arizona State University have sequenced the genome of the cyanobacterium Acaryochloris marina, the only well-studied photosynthetic species that contains chlorophyll d (Chl d) as the major photosynthetic pigment. Chlorophyll d absorbs “red edge,” near-infrared, long wavelength light.

The extension of Chl d absorption into the near-infrared, beyond the range of any other oxygenic photosynthetic organisms, could have immense agricultural consequences, noted the project team. If Chl d could be incorporated into higher plants, it has a potential capacity of increasing the energy conversion of sunlight by 5% compared to that of the chlorophyll a-containing organisms.

Robert Blankenship Ph.D., Lucille P. Markey Distinguished Professor in Arts & Sciences at Washington University, and principal investigator of the project, said with every gene of Acaryochloris marina now sequenced and annotated, the immediate goal is to find the enzyme that causes a chemical structure change in chlorophyll d, making it different from primarily chlorophyll a, and b, but also from about nine other forms of chlorophyll.

The synthesis of chlorophyll by an organism is complex, involving 17 different steps in all. Some place near the end of this process an enzyme transforms a vinyl group to a formyl group to make chlorophyll d. This transformation of chemical forms is not known in any other chlorophyll molecules.

—Robert Blankenship

Blankenship said he and his collaborators have some candidate genes they will test. They hope to insert these genes into an organism that makes just chlorophyll a.

We now have genetic information on a unique organism that makes this type of pigment that no other organism does. We don’t know what all the genes do by any means. But we’ve just begun the analysis. When we find the chlorophyll d enzyme and then look into transferring it into other organisms, we’ll be working to extend the range of potentially useful photosynthesis radiation.

—Robert Blankenship

Blankenship and his colleagues from both institutions are publishing a paper on their work in the 4 February online edition of the Proceedings of the National Academy of Sciences. The work was supported by the National Science Foundation and also involved collaborators from Australia and Japan. Three Washington University undergraduate students and one graduate student participated in the project, as well as other research personnel.

Acaryochloris marina was discovered 11 years ago, living in a symbiotic relationship with a colonial ascidian (sea squirt) in Australia’s Great Barrier Reef. The Acaryochloris marina lives beneath the sea squirt, which is a marine animal that lives attached to rocks just below the surface of the water. The cyanobacterium absorbs “red edge” light through the tissues the sea squirt.

Acaryochloris marina lies down there using that far red light that no one else can use. The organism has never been under very strong selection pressure to be lean and mean like other bacteria are. It’s kind of in a sweet spot. Living in this environment is what allowed it to have such dramatic genome expansion.

—Robert Blankenship

As a result, its genome is massive for a cyanobacterium, comprising 8.3 million base pairs, and sophisticated. The genome is among the very largest of 55 cyanobacterial strains in the world sequenced thus far, and it is the first chlorophyll d–containing organism to be sequenced.

Other related organisms are being discovered. Researchers from the University of Oregon and the University of Montana found a strain related to Acaryochloris marina during a biotic inventory of the Salton Sea in California. In contrast to A. marina, however, which lives in clean oceanic waters, Acaryochloris 2A51 lives in a hypereutrophic high salinity environment.

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February 5, 2008 in Biomass, Biotech | Permalink | Comments (21) | TrackBack (0)

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Fascinating that any phototropic life is found in the Salton Sea. Which bodes well for life (and perhaps derivative substances) in the most inhospitable of places.

I wonder if GM algae capable of utilizing near-infrared radiation could continue to produce some biomass at night. The radiation source could be flue gases from a coal-fired power plant that also provides the CO2. The trick, of course, would be to filter out the useful frequencies to avoid frying the little critters.

One worry is that isolating and adding this unusual photosynthetic pathway to regular algae could bestow an evolutionary advantage on them. After all, such an organism would not be burdened by the maintenance of the massive genome of Ac. marina. If an advantage were to result, any genetically modified algae that escape into the wild - and some will - could become an invasive pest.

5%.  I wonder how much of a difference this could make to viability of plants under stress?

Rafael, if a cyanobacterium could photosynthesize from thermal IR it would be able to generate chemical energy from its own heat (violation of 2LOT).  This is near-edge IR around 800 nanometers, not thermal IR at 12000 nm.

@ Engineer-Poet -

fair point. Are there any artificial sources of near-edge IR near power plants that could be leveraged at night or, is sunlight the only viable source?

At one point here on GCC there was a suggestion that the color temp of the fluid bed process might contain enough in the IR range:

Fluidized bed combustion:

2898/1100K = 2580.5 nm

I guess there'd be some light at 700-1000nm which could be used for algal growth at night. The trick would be to pipe the algal soup into the combustion area without frying it.

And if the GM variety was also highly saline dependent - it might not survive in the wild.

Rafael, think about the conversion losses before you take that thought any further.

I suspect the energy content of slowly radiating heat sources would not have a significant impact, compared to, oh, say, direct sunlight.

As to whether the 5% would confer a significant evolutionary benefit, we should look at whether the cyanobacteria seem to have an advantage over similar non-chlorphyl d organisms.

Also, if we modify algae with this chlorophyl-d, they still might not be very competitive. One of the problems with the high-lipid algaes is that they are not very competitive. Maybe that's a good thing. They could be highly productive in bioreactors, but unlikely to do much if they escape.

EP:

You are right on frequency, but wrong on second law. Second law defines heat transfer direction between macroscopic bodies without applied mechanical energy.

First, photosynthesis is molecular event, not macroscopic, so second law does not apply. This is why any endothermic reaction is possible in chemistry, and this is why evaporation from surface of cold water or even ice could take place.

Second, there is transfer of heat energy into energy of chemical bonds, which is not subject of second law.

In practical terms, only first law for conservation of energy could be applied to hypothetical case when thermal IR emission of the body is used by same body to produce chemical energy. The body will cool down exactly by amount of heat energy converted to chemical energy.

Something like a chameleon?

First, photosynthesis is molecular event, not macroscopic, so second law does not apply. This is why any endothermic reaction is possible in chemistry, and this is why evaporation from surface of cold water or even ice could take place.

The second law applies universally. If you think it doesn't apply, you have used it incorrectly.

Perhaps a strain that is phototropic in the 2500nm frequency could be engineered. In which case one species can grown under radiant light from the burn and another from solar during sunup.

Paul Dietz:

Take two macroscopic bodies, one hot, another warm. Both bodies emit IR radiation, according to their temperature. Second law of thermodynamics requires that net heat transfer should be from hot to warm body.

Now, on atomic level, “warm” atom from warm body emits electromagnetic quantum of IR radiation, which is adsorbed by “hot” atom of hot body. You have transfer of heat energy from warm to hot body (atoms).

What I described is roughly how GHG of atmosphere “heat” much warmer surface of Earth. Net heat energy transfer is still from hot to warm body – Earth surface heats atmosphere. But on molecular level, where quantum effects prevail, second law is not applicable.

Second law defines heat transfer direction between macroscopic bodies without applied mechanical energy.
Two words:  Maxwell's Demon.
“warm” atom from warm body emits electromagnetic quantum of IR radiation, which is adsorbed by “hot” atom of hot body.
While more photons go from hot to warm than vice versa.
What I described is roughly how GHG of atmosphere “heat” much warmer surface of Earth.
What you have described is like one spin of an unobservable roulette wheel, when all we can measure is the odds favoring the house.

Jeee, guys, get a habit to consult at minimum Wiki before wearing your fingers over a keyboard:

“Thermodynamics is a theory of macroscopic systems at equilibrium and therefore the second law applies only to macroscopic systems with well-defined temperatures. No violation of the second law of thermodynamics has ever been observed in a macroscopic system. But on scales of a few atoms, the second law does not apply; for example, in a system of two molecules, it is possible for the slower-moving ("cold") molecule to transfer energy to the faster-moving ("hot") molecule. Such tiny systems are outside the domain of thermodynamics, but they can be investigated using statistical mechanics. For any isolated system with a mass of more than a few picograms, the second law is true to within a few parts in a million.”

http://en.wikipedia.org/wiki/Second_law_of_thermodynamics

Second Law does not apply even to macroscopic systems, when: a)system is not at equilibrium, b)system is not isolated. The classic example of such system where second law is meaningless is combustion of fuel, while it lasts.

Yeah, like chemical reactions aren't driven in the direction given by Gibb's free energy (which is intimately connected to the 2nd Law).

Again, EP, Gibbs law is applicable only to closed thermodynamic system.

Returning to the subject of the article, second law does not prohibit concentration of energy (not just heat energy) by photosynthesis system, because such system in nature is not closed and not at equilibrium. The example of such process is concentration of low-density solar energy into highly concentrated form we successfully use, such as coal.

Photosynthetic systems can be analyzed by thermodynamic principles, like any other open system; you just have to draw the control boundary and account for everything crossing it.

Seriously, Andrey, you're making a real fool of yourself.

Of course photosynthesis systems could be analyzed by thermodynamic principles. By one who understand how to apply it correctly.

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