Alternative Energy Creation

For most of the history of biology, plants and animals have been thought of in two separate categories: autotrophs and heterotrophs.

Autotrophs are organisms that provide their own food sources. Plants do this by capturing sunlight and using a process called photosynthesis, where carbon dioxide and water are converted into carbohydrates and oxygen.

Carbon dioxide + Water → Carbohydrates + Oxygen

Heterotrophs are organisms that consume other organisms for food. Whether animals are herbivores, omnivores, or carnivores, they are eating other organisms to acquire energy.

For most of biology, this has been the general framework. Plants make their own energy from sunlight. Animals consume plants, animals, or both to get the energy they need. However, there are exceptions that have been called photoheterotrophs or mixotrophs.

Most corals, for example, can both synthesize energy from sunlight and consume organisms like plankton. The Venus flytrap, along with other insect-eating plants, can derive energy from sunlight and from the organisms they consume. Other examples include certain types of non-sulfur bacteria, heliobacteria, many types of plankton, and even some insects.

Humans, however, have generally been understood as purely heterotrophic. We need to eat plants and animals of various kinds to get our energy.

That may still be true in the most basic sense, but research into light, mitochondria, and cellular energy production adds an interesting layer to the conversation.

Hundreds of studies have found that human cells, specifically the mitochondria inside our cells, can produce more ATP when exposed to red and near-infrared light. ATP, or adenosine triphosphate, is the primary energy currency of the cell.

The research goes even further than that. A study published in the Journal of Cell Science found that other organisms, including mammals that are biologically similar to humans, such as rodents and pigs, were shown to be capable of taking up chlorophyll metabolites into their mitochondria. Those metabolites were then able to help capture sunlight energy and amplify cellular energy production. The study was titled “Light-harvesting chlorophyll pigments enable mammalian mitochondria to capture photonic energy and produce ATP.”

The research suggests that some animals can use these chlorophyll metabolites to speed up the rate of energy production and increase the overall volume of ATP produced by fairly large amounts in many cases.

Here is a key passage from the abstract of that study:

“Sunlight is the most abundant energy source on this planet. However, the ability to convert sunlight into biological energy in the form of adenosine-5′-triphosphate (ATP) is thought to be limited to chlorophyll-containing chloroplasts in photosynthetic organisms. Here we show that mammalian mitochondria can also capture light and synthesize ATP when mixed with a light-capturing metabolite of chlorophyll.”

This does not mean humans are plants, and it does not mean food is unnecessary. Humans still acquire energy primarily by consuming food. However, the research does suggest that our relationship with light may be more biologically meaningful than the traditional autotroph-versus-heterotroph model makes it seem.

Another related paper, “Light Effect on Water Viscosity: Implication for ATP Biosynthesis,” explored how near-infrared light may influence ATP synthesis through effects on intramitochondrial water viscosity. The authors proposed a physicochemical mechanism that could help explain why non-destructive levels of near-infrared light have been associated with increases in ATP synthesis.

Taken together, these findings point toward a broader idea: light may play a more direct role in cellular energy production than previously assumed.

For most of biology, we have drawn a clear line between organisms that make energy from sunlight and organisms that must consume other organisms for energy. That distinction is still useful, but it may not tell the whole story. Some organisms clearly blur that line, and research into mammalian mitochondria suggests there may be more overlap than once believed.

At minimum, this research gives us a reason to think more carefully about sunlight, red light, near-infrared light, chlorophyll metabolites, mitochondria, and ATP production. Energy creation in biology may not be as simple as plants make energy from light and animals get energy only from food.

The body may be more responsive to light than the older model allowed us to see.

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References

Xu, C., Zhang, J., Mihai, D. M., & Washington, I. “Light-harvesting chlorophyll pigments enable mammalian mitochondria to capture photonic energy and produce ATP.” Journal of Cell Science 127, no. 2, 388–399, 2014. https://doi.org/10.1242/jcs.134262

Sommer, A. P., Haddad, M. K., & Fecht, H. J. “Light Effect on Water Viscosity: Implication for ATP Biosynthesis.” Scientific Reports 5, 12029, 2015. https://doi.org/10.1038/srep12029