Understanding Algae's 'dimmer switch': joint study from Constructor University and Princeton sheds new light on how algae regulate photosynthesis with pH

A new joint study from Constructor University and Princeton University has discovered a "dimmer switch" used by certain algae to control light harvesting at the molecular level. The mechanism found in Cryptophyte algae—single-celled organisms that perform photosynthesis in low-light, underwater environments—responds to pH changes in the algae's internal environment, prompting special pigment molecules to dial energy capture up or down. Published in the Journal of the American Chemical Society, the study combined Constructor's computational expertise with Princeton's experimental capabilities to reveal the previously unknown regulatory system that could have implications for climate-adaptive agriculture and pharmaceutical research.

The study centers on PC645, a protein complex that contributes to cryptophyte algae’s renowned ability to photosynthesize efficiently using specialized light-harvesting pigments that can capture energy from the dim, blue-green underwater light. During photosynthesis, the pH inside the algae can fluctuate significantly, affecting how it manages light energy. The Constructor-Princeton team found that certain pigments within PC645 called mesobiliverdins (MBVs) act as pH-sensitive regulators, modulating how efficiently the organism harvests light in response to fluctuating pH levels. It’s a novel discovery that could have fascinating implications, if scientists can determine its underlying purpose.

"We've effectively found the dimmer switch, but we don't actually know what it's for yet," explained Professor of Theoretical Physics Dr. Ulrich Kleinekathöfer, who led the Constructor University team. "We now know there is a mechanism that responds dynamically to pH changes, and we have some ideas and assumptions about its purpose, but further investigation will be needed."

Complementary Collaboration  

The research combined the complementary and interdisciplinary expertise of both Constructor University and Princeton researchers. Prof. Kleinekathöfer’s Computational Physics and Biophysics Group performed sophisticated computer simulations to model how the pigments behave at different pH levels. A team of researchers at Princeton University, led by Professor Gregory Scholes—Editor-in-Chief of the Journal of Physical Chemistry Letters and a Fellow of the Royal Society—conducted experimental measurements using spectroscopy to successfully validate the computational predictions.

The collaboration revealed that when pH levels fluctuate, the MBV pigments undergo changes to their vibrational properties that alter their energy transfer rates by a factor of two to three, essentially turning the dimmer switch on their light-harvesting efficiency down as pH increases, and back up when it decreases. Prof. Kleinekathöfer’s computational models quantitatively reproduced the experimental observations, showing approximately 40-50% quenching of fluorescence at high pH.

The research also revealed that this pH-dependent regulatory mechanism may be conserved across multiple types of photosynthetic proteins, suggesting it could represent a general strategy that photosynthetic organisms use to respond to environmental changes. The team found similar structural features in related protein complexes, indicating that the dimmer switch mechanism might be more widespread than initially thought.  

"If we can understand the mechanism and find ways to modify it, this is the kind of thing that could one day be used in biomedical or pharmaceutical applications, or to modify crop yields for example in response to our changing climate," said Kleinekathöfer. "People can be wary of genetic modifications because they can introduce adaptations immediately that nature would typically require a very long timescale to produce. But we also live in a time when our changing climate is causing rapid changes to our environment. Being able to facilitate these kinds of modifications and adaptations could be a helpful or even necessary tool for responding to the kinds of major challenges we're encountering due to our changing climate.”

Life on a quantum scale: combining quantum mechanics and biology

The study offers a fascinating glimpse into the direction of quantum biology—a relatively new and intrinsically interdisciplinary field that explores how quantum phenomena occur in biological systems. "As a theoretical physicist, seeing biology, chemistry and physics all work together to give us new understanding and new perspectives on our natural world is very rewarding," said Prof. Kleinekathöfer. "When we're really in the thick of it, the boundaries between the fields can break down completely, which is part of what makes it such an exciting area of research."

Prof. Kleinekathöfer and his Computational Physics and Biophysics research group at Constructor University are dedicated to combining quantum mechanics, quantum chemistry and molecular biology. In addition to the Princeton collaboration, Prof. Kleinekathöfer serves as the lead coordinator of PhotoCaM, a €2.6 million European Union-funded doctoral training network focused on photosynthesis and quantum effects therein.

Through PhotoCaM, Prof. Kleinekathöfer and is network are helping to train the next generation of computational scientists who can explore interdisciplinary and complex problems like light harvesting on a molecular level, positioning Constructor University as a leader in this emerging field.