Light-Harvesting Bacteria Reveal Photonic Defense Mechanism

Rhodospirillum Photometricum has a mechanism that allows it to harvest more light in dim conditions but protect its cellular machinery from photon damage when it’s too bright.

A few years ago, scientists studying the light-harvesting bacteria, Rhodospirillum Photometricum, made a curious discovery. This bacteria is able to exploit solar energy because its cell membrane is filled with chromophore vesicles: regions containing pigment molecules capable of absorbing light and turning it into chemical fuel.

The strange thing about these bacteria was that the membrane came in two forms: one form with large numbers of pigment molecules and another with only a few. And the difference was determined by the amount of light the organism had been exposed to. Why should that be?

Today, Neil Johnson at the University of Miami and a few pals explain why with the aid of a sophisticated model of the behaviour of the membrane. They say that the membrane performs two competing functions. First, it needs to convert large numbers of photons into useful chemical energy. Second, it must protect the inside of the cell from an oversupply of photonic energy and the damage it can cause. Johnson and co say the puzzle is explained by the interplay of these two forces which cause the membrane to form one way or the other.

That’s an interesting insight and not just because it explains the structural differences that appear during the growth of Rhodospirillum Photometricum. Johnson and co hint that a similar approach might be useful for creating a new generations of solar cells. They say: “this new quantitative understanding may help accelerate development of novel solar micropanels mimicking natural designs.”

I guess the important point is that if we want to copy nature’s machinery for harvesting light, we’ll also need to copy the defensive mechanisms that evolved to protect this machinery from over exposure to sunlight. Rather like sun cream for solar cells.

Ref: arxiv.org/abs/1003.2443: Light-Harvesting In Bacteria Exploits A Critical Interplay Between Transport and Trapping Dynamics