Bacteria Know How To Harness Quantum Mechanics, Study Finds

Photosynthetic organisms harvest sunlight to produce the energy they need to survive. A new article published by researchers at the University of Chicago reveals their secret: the exploitation of quantum mechanics.

“Before this study, the scientific community saw quantum signatures generated in biological systems and wondered, were these results simply a consequence of building biology from molecules, or did they have a purpose? said Greg Engel, chemistry professor and lead author of the study. “This is the first time that we have seen biology actively harness quantum effects.”

Scientists have studied a type of microorganism called green sulfur bacteria. These bacteria need light to survive, but even small amounts of oxygen can damage their delicate photosynthetic equipment. They must therefore develop ways to minimize the damage when the bacteria encounters oxygen.

To study this process, the researchers tracked the movement of energy through a photosynthetic protein under different conditions – with oxygen around and without oxygen.

They found that the bacteria uses a quantum mechanical effect called vibronic mixing to move energy between two different pathways, depending on whether or not there is oxygen. Vibratory mixing involves vibrational and electronic characteristics in the coupling of molecules to each other. In essence, vibrations blend so completely with electronic states that their identities become inseparable. This bacteria uses this phenomenon to guide energy where it needs it.

If there is no oxygen and the bacteria are safe, the bacteria use a vibronic mixture by matching the energy difference between two electronic states in an assembly of molecules and proteins called the FMO complex, with the energy of the vibration of a bacteriochlorophyll molecule. This encourages energy to flow through the “normal” pathway to the photosynthetic reaction center, which is filled with chlorophyll.

But if there is oxygen around, the organism has evolved to direct the energy through a less direct path where it can be turned off. (Quenching energy is similar to putting a palm on a vibrating guitar string to dissipate the energy.) This way the bacteria lose energy but save the whole system.

To achieve this effect, a pair of cysteine ​​residues in the photosynthetic complex act as a trigger: they each react with oxygen in the environment by losing a proton, which disrupts vibronic mixing. This means that energy now preferably passes through the alternative route, where it can be safely switched off. This principle is a bit like blocking two lanes on a freeway and diverting some traffic to local roads where there are many more exits.

“What’s interesting about this result is that we see the protein activate and deactivate vibronic coupling in response to environmental changes in the cell,” said Jake Higgins, a graduate student in the Department of Chemistry and lead author. of the article. “The protein uses the quantum effect to protect the body from oxidative damage.”

These findings bring an exciting new revelation in biology; the use of an explicitly quantum mechanism to protect the system shows significant adaptation and that quantum effects may be important for survival.

This phenomenon is probably not limited to green sulfur bacteria, the scientists said. As Higgins explained, “The simplicity of the mechanism suggests that it could be found in other photosynthetic organisms across the evolutionary landscape. If more organisms are able to dynamically modulate quantum mechanical couplings in their molecules to produce larger changes in physiology, there could be a whole new set of inherently selected effects that we don’t yet know about. ”