Bacteria know how to exploit quantum mechanics, research shows

Photosynthetic organisms harvest light from the sun to produce the energy they need to survive. A new paper published by researchers at the University of Chicago reveals their secret: exploiting quantum mechanics.

“Before this study, the scientific community saw quantum signatures generated in biological systems and posed the question: were these results just a result of the biology made up of molecules, or did they serve a purpose?” said Greg Engel, chemistry professor and senior author of the study. “This is the first time that we have seen biology actively use quantum effects.”

The scientists 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. So they have to figure out ways to minimize the damage when the bacteria comes into contact with oxygen.

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

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 oxygen is nearby. Vibronic mixing involves vibrational and electronic features in molecules that couple together. In essence, the vibrations blend so completely with the electronic states that their identities become inseparable. This bacterium uses this phenomenon to direct energy where it needs it.

When there is no oxygen nearby and the bacterium is safe, the bacterium uses vibronic mixing by matching the energy difference between two electronic states in a collection of molecules and proteins called the FMO complex with the energy of the vibration of a bacteriochlorophyll molecule . This stimulates the energy to flow through the ‘normal’ path to the photosynthetic reaction center, which is full of chlorophyll.

But if oxygen is nearby, the organism has evolved to send the energy through a less direct path where it can be extinguished. (Quenching energy is similar to placing a palm on a vibrating guitar string to dissipate energy.) In this way, the bacteria loses some energy but saves the entire system.

To achieve this effect, a few cysteine ​​residues in the photosynthetic complex act as a trigger: they each react with the oxygen in the environment by losing a proton, which disrupts vibronic mixing. This means that energy now preferentially moves through the alternate path where it can be safely extinguished. This principle is a bit like blocking two lanes on a highway and diverting traffic to local roads with many more exits.

“What’s interesting about this result is that we see the protein turn the vibronic link on and off in response to changes in the environment in the cell,” said Jake Higgins, a graduate student in the Department of Chemistry and the lead author of the study. article. “The protein uses the quantum effect to protect the organism from oxidative damage.”

These findings lead to an exciting new revelation about biology; the use of an explicit quantum mechanism to protect the system shows an important adaptation and that quantum effects can be important for survival.

This phenomenon is likely not limited to green sulfur bacteria, the scientists said. As Higgins explained, “The simplicity of the mechanism suggests that it can be found in other photosynthetic organisms in the evolutionary landscape. there’s a whole new set of effects selected by nature that we don’t know yet. ”