Learning About Photosynthesis from Purple Bacteria

In nature, it would appear that purple is indeed the new green. Actually, it's been this way since the beginning of time, but it's only now that investigators are finally beginning to realize the massive superiority that purple bacteria have over their green counterparts in producing energy from sunlight. Scientists hope to use the new investigations to produce more advanced solar panels, that would feature higher photon-conversion rates, and therefore be more efficient.

When life emerged on Earth, the tiny purple bacteria were among the organisms in the front lines. These single-cells constructs play a fundamental role in sustaining life on our planet, researchers believe, even if they live at the bottom of lakes and on coral reefs. They appear to prefer aquatic environments, which is another indicator of their early evolution. Sunlight is their main source of energy, and they are very efficient in converting the small amounts of light that penetrate the water to their depth into energy with which to grow.

A team of investigators from the University of Miami, led by physicist Neil Johnson, now hopes to be able to mimic cellular arrangement identified in purple bacteria in order to produce a new generation of solar panels. The expert, who is also the head of the inter-disciplinary research group in complexity in the College of Arts and Sciences at the university, adds that other energy-conversion devices could also benefit from this type of study. Preliminary data of the team's analysis appeared in the latest issue of the esteemed scientific journal Physical Review Letters.

“These bacteria have been around for billions of years, you would think they are really simple organisms and that everything is understood about them. However, purple bacteria were recently found to adopt different cell designs depending on light intensity. Our study develops a mathematical model to describe the designs it adopts and why, which could help direct design of future photoelectric devices,” explains Johnson. The scientists collaborated closely with colleagues from the Universidad de los Andes in Colombia for the new investigation. The paper accompanying the findings is entitled “Light-harvesting in bacteria exploits a critical interplay between transport and trapping dynamics.”

“One might assume that the more light the cell receives, the more open reaction centers it has. However, that is not always the case, because with each new generation, purple bacteria create a design that balances the need to maximize the number of photons trapped and converted to chemical energy, and the need to protect the cell from an oversupply of energy that could damage it,” the team leader adds.

“Imagine a really busy day at the supermarket, if the reaction center is busy it's like the cashier is busy, somebody is doing the bagging," Johnson says. "The shopper wonders around to find an open checkout and some of the shoppers may get fed up and leave…The bacteria are like a very responsible supermarket. They would rather lose some shoppers than have congestion on the way out, but it is still getting enough profit for it to survive,” Johnson says of the active modifications purple bacteria undergo in order to maximize the amount of energy they produce.