Revolutionary Discovery – Newly Identified Process Could Account for 12% of Global Oxygen Production

An illustrative image of diatoms, single-celled algae distinguished for their decorative silica cell walls. Credit: Daniel Yee

The oxygen in every tenth breath you take can be attributed to a cellular process in tiny marine algae.

Breathe deeply. Now repeat it nine times more. One out of the ten breaths you just inhaled was enabled by a recently discovered cellular process that stimulates photosynthesis in marine phytoplankton, suggests new research.

Dubbed “revolutionary” by a research team at UC San Diego’s Scripps Institution of Oceanography, this previously unknown process is credited with contributing between 7% and 25% of all oceanic oxygen production and carbon fixation. When considering photosynthesis on land, this process is thought to contribute to roughly 12% of the total global oxygen production.

The vital role of phytoplankton, microscopic organisms that float in aquatic ecosystems, is well-known to scientists due to their photosynthetic capabilities. These minuscule ocean-dwelling algae are integral to the aquatic food chain and are estimated to produce about half of the Earth’s oxygen.

The recent study, released on May 31 in the journal Current Biology, outlines how a proton-pumping enzyme (known as VHA) facilitates global oxygen production and carbon fixation from phytoplankton.

“This research signifies a significant advancement in our understanding of marine phytoplankton,” stated lead author Daniel Yee, who conducted the study during his Ph.D. at Scripps Oceanography and now holds a joint postdoctoral position at the European Molecular Biology Laboratory and University of Grenoble Alpes in France. “Through eons of evolution, these tiny ocean cells have developed minute chemical reactions, particularly this mechanism that boosts photosynthesis, which has profoundly influenced the course of life on Earth.”

In collaboration with Scripps physiologist Martín Tresguerres, one of his advisors, and other partners at Scripps and the Lawrence Livermore National Laboratory, Yee unveiled the intricate inner mechanisms of a group of phytoplankton known as diatoms, single-celled algae recognized for their intricately crafted silica cell walls.

Understanding the “proton pump” enzyme

Previous studies in the Tresguerres Lab aimed to determine how the VHA enzyme is used by various organisms in processes vital for oceanic life. This enzyme, present in almost all life forms, from humans to single-celled algae, fundamentally modifies the pH level of its surrounding environment.

“We conceptualize proteins as Lego blocks,” Tresguerres, a co-author of the study, elaborated. “The proteins always perform the same function, but they can achieve a greatly diverse functionality depending on the other proteins they pair with.”

In humans, this enzyme helps kidneys regulate blood and urine functions. Giant clams use it to dissolve coral reefs by secreting an acid to burrow into the reef for shelter. Corals use the enzyme to enhance photosynthesis in their symbiotic algae, while deep-sea worms, Osedax, use it to dissolve the bones of marine mammals like whales for consumption. The enzyme is also present in the gills of sharks and rays, where it’s part of a mechanism that adjusts blood chemistry. And in fish eyes, the proton pump facilitates oxygen delivery that improves vision.

Given this prior research, Yee became intrigued about how the VHA enzyme functioned in phytoplankton. He sought to answer this question by merging advanced microscopy techniques in the Tresguerres Lab with genetic tools developed in the lab of the late Scripps scientist Mark Hildebrand, a leading diatom expert and one of Yee’s advisors.

Employing these tools, Yee managed to mark the proton pump with a fluorescent green tag and precisely locate it around chloroplasts, specialized structures in diatom cells. These chloroplasts have an extra membrane compared to other algae, encasing the space where carbon dioxide and light energy are transformed into organic compounds and oxygen is released.

“We managed to produce these images that display the protein of interest and its location within a cell with multiple membranes,” Yee commented. “Alongside detailed photosynthesis quantification experiments, we discovered that this protein enhances photosynthesis by delivering more carbon dioxide, which the chloroplast uses to generate more complex carbon molecules, like sugars, and concurrently produces more oxygen.”

Link to evolution

After determining the underlying mechanism, the team connected it to various aspects of evolution. Diatoms evolved from a symbiotic event approximately 250 million years ago, where a protozoan and an algae merged into one organism, a process known as symbiogenesis. The authors underscore that phagocytosis, one cell consuming another, is a common occurrence in nature, and it relies on the proton pump to digest the cell serving as the food source. In the case of diatoms, an unusual event occurred where the consumed cell was not fully digested.

“Instead of one cell digesting the other, the acidification driven by the proton pump of the predator ended up promoting photosynthesis by the ingested prey,” Tresguerres explained. “Over evolutionary time, these two separate organisms fused into one, which we now call diatoms.”

As not all algae possess this mechanism, the authors speculate that this proton pump has provided diatoms with a photosynthetic advantage. They also note that when diatoms emerged 250 million years ago, atmospheric oxygen levels significantly increased, and the newly discovered algae mechanism may have contributed to this event.

It’s widely believed that the majority of fossil fuels we extract come from biomass that sank to the ocean floor, including diatoms, over millions of years, culminating in the formation of oil reserves. The researchers hope their study can inform biotechnological strategies to enhance photosynthesis, carbon sequestration, and biodiesel production. They also believe it will lead to a better understanding of global biogeochemical cycles, ecological interactions, and the impacts of environmental changes, like climate change.

“This study is one of the most thrilling in the field of symbiosis in recent decades, and it will significantly impact future research globally,” Tresguerres predicted.

Reference: “The V-type ATPase enhances photosynthesis in marine phytoplankton and further links phagocytosis to symbiogenesis” by Daniel P. Yee, Ty J. Samo, Raffaela M. Abbriano, Bethany Shimasaki, Maria Vernet, Xavier Mayali, Peter K. Weber, B. Greg Mitchell, Mark Hildebrand, Johan Decelle and Martin Tresguerres, 31 May 2023, Current Biology.
DOI: 10.1016/j.cub.2023.05.020

Additional collaborators include Raffaela Abbriano, Bethany Shimasaki, Maria Vernet, Greg Mitchell, and the late Mark Hildebrand of Scripps Oceanography; Ty Samo, Xavier Mayali, and Peter Weber of the Lawrence Livermore National Laboratory; and Johan Decelle of University of Grenoble Alpes.

The study did not receive any specific funding. Yee’s doctoral studies at Scripps Oceanography were supported by the Scripps Fellowship, the NIH training grant, and the Ralph Lewin Graduate Fellowship. The Arthur M. and Kate E. Tode Research Endowment in Marine Biological Sciences at UC San Diego funded the purchase of an essential microscope for the research.

Frequently Asked Questions (FAQs) about Marine Phytoplankton Oxygen Production

More about Marine Phytoplankton Oxygen Production

• Scripps Institution of Oceanography at UC San Diego
• European Molecular Biology Laboratory
• University of Grenoble Alpes
• Lawrence Livermore National Laboratory
• Current Biology Journal
• Information on Marine Phytoplankton
• Basics on Photosynthesis
• Information on Diatoms