Phenomenal phytoplankton: Scientists uncover cellular process behind
oxygen production
One out of 10 breaths contains oxygen generated by cellular mechanism in microscopic algae

Date:
May 31, 2023
Source:
University of California - San Diego
Summary:
According to new research, the amount of oxygen in one of 10 breaths
was made possible thanks to a newly identified cellular mechanism
that promotes photosynthesis in marine phytoplankton. The new
study identifies how a proton pumping enzyme (known as VHA) aids
in global oxygen production and carbon fixation from phytoplankton.


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FULL STORY ==========================================================================
Take a deep breath. Now take nine more. According to new research, the
amount of oxygen in one of those 10 breaths was made possible thanks to
a newly identified cellular mechanism that promotes photosynthesis in
marine phytoplankton.

Described as "groundbreaking" by a team of researchers at UC San Diego's Scripps Institution of Oceanography, this previously unknown process
accounts for between 7% to 25% of all the oxygen produced and carbon
fixed in the ocean.

When also considering photosynthesis occuring on land, researchers
estimated that this mechanism could be responsible for generating up to
12% of the oxygen on the entire planet.

Scientists have long recognized the significance of phytoplankton -
- microscopic organisms that drift in aquatic environments -- due to
their ability to photosynthesize. These tiny oceanic algae form the
base of the aquatic food web and are estimated to produce around 50%
of the oxygen on Earth.

The new study, published May 31 in the journal Current Biology,
identifies how a proton pumping enzyme (known as VHA) aids in global
oxygen production and carbon fixation from phytoplankton.

"This study represents a breakthrough in our understanding of marine phytoplankton," said lead author Daniel Yee, who conducted the research
while a PhD student at Scripps Oceanography and currently serves as
a joint postdoctoral researcher at the European Molecular Biology
Laboratory and University of Grenoble Alpes in France. "Over millions
of years of evolution, these small cells in the ocean carry out minute
chemical reactions, in particular to produce this mechanism that enhances photosynthesis, that shaped the trajectory of life on this planet."
Working closely with Scripps physiologist Marti'n Tresguerres, one of
his co- advisors, and other collaborators at Scripps and the Lawrence
Livermore National Laboratory, Yee unraveled the complex inner workings
of a specific group of phytoplankton known as diatoms, which are
single-celled algae famous for their ornamental cell walls made of silica.

Understanding the "proton pump" enzyme Previous research in the
Tresguerres Lab has worked to identify how VHA is used by a variety of organisms in processes critical to life in the oceans. This enzyme is
found in nearly all forms of life, from humans to single-celled algae, and
its basic role is to modify the pH level of the surrounding environment.

"We imagine proteins as Lego blocks," explained Tresguerres, a study
co-author.

"The proteins always do the same thing, but depending on what other
proteins they are paired with, they can achieve a vastly different
function." In humans, the enzyme aids kidneys in regulating blood and
urine functions.

Giant clams use the enzyme to dissolve coral reefs, where they secrete an
acid that bores holes in the reef to take shelter. Corals use the enzyme
to promote photosynthesis by their symbiotic algae, while deep-sea worms
known as Osedax use it to dissolve the bones of marine mammals, such
as whales, so they can consume them. The enzyme is also present in the
gills of sharks and rays, where it is part of a mechanism that regulates
blood chemistry. And in fish eyes, the proton pump helps deliver oxygen
that enhances vision.

Looking at this previous research, Yee wondered how the VHA enzyme
was being used in phytoplankton. He set out to answer this question
by combining high- tech microscopy techniques in the Tresguerres Lab
and genetic tools developed in the lab of the late Scripps scientist
Mark Hildebrand, who was a leading expert on diatoms and one of Yee's co-advisors.

Using these tools, he was able to label the proton pump with a fluorescent green tag and precisely locate it around chloroplasts, which are known
as "organelles" or specialized structures within diatom cells. The
chloroplasts of diatoms are surrounded by an additional membrane compared
to other algae, enveloping the space where carbon dioxide and light
energy are converted into organic compounds and released as oxygen.

"We were able to generate these images that are showing the protein
of interest and where it is inside of a cell with many membranes," said
Yee. "In combination with detailed experiments to quantify photosynthesis,
we found that this protein is actually promoting photosynthesis by
delivering more carbon dioxide, which is what the chloroplast uses to
produce more complex carbon molecules, like sugars, while also producing
more oxygen as a by-product." Connection to evolution Once the underlying mechanism was established, the team was able to connect it to multiple
aspects of evolution. Diatoms were derived from a symbiotic event between
a protozoan and an algae around 250 million years ago that culminated into
the fusing of the two organisms into one, known as symbiogenesis. The
authors highlight that the process of one cell consuming another, known
as phagocytosis, is widespread in nature. Phagocytosis relies on the
proton pump to digest the cell that acts as the food source. However,
in the case of diatoms, something special occurred in which the cell
that was eaten didn't get 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," said Tresguerres. "Over evolutionary time, these
two separate organisms fused into one, for what we now call diatoms."
Not all algae have this mechanism, so the authors think that this proton
pump has given diatoms an advantage in photosynthesis. They also note that
when diatoms originated 250 million years ago, there was a big increase
in oxygen in the atmosphere, and the newly discovered mechanism in algae
might have played a role in that.

The majority of fossil fuels extracted from the ground are believed
to have originated from the transformation of biomass that sank to
the ocean floor, including diatoms, over millions of years, resulting
in the formation of oil reserves. The researchers are hopeful that
their study can provide inspiration for biotechnological approaches
to improve photosynthesis, carbon sequestration, and biodiesel
production. Additionally, they think it will contribute to a better understanding of global biogeochemical cycles, ecological interactions,
and the impacts of environmental fluctuations, such as climate change.

"This is one of the most exciting studies in the field of symbiosis
in the past decades and it will have a large impact on future research worldwide," said Tresguerres.

Additional co-authors 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 authors did not receive any funding for this study. Yee's doctoral
studies at Scripps Oceanography were supported by the Scripps Fellowship,
the NIH training grant, and the Ralph Lewin Graduate Fellowship. Funds by
UC San Diego's Arthur M. and Kate E. Tode Research Endowment in Marine Biological Sciences supported the purchase of a microscope that was
essential for the research.

* RELATED_TOPICS
o Plants_&_Animals
# Marine_Biology # Botany # Sea_Life # Biology
o Earth_&_Climate
# Global_Warming # Oceanography # Environmental_Awareness
# Ecology
* RELATED_TERMS
o Phytoplankton o Dead_zone_(ecology) o Carbon_dioxide o
Plankton o Plant o Oxygen o Breath o Algal_bloom

========================================================================== Story Source: Materials provided by
University_of_California_-_San_Diego. Original written by Brittany
Hook. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Daniel P. Yee et al. Report|Online Now PDF Figures Save Reprints
Request
The V-type ATPase enhances photosynthesis in marine phytoplankton
and further links phagocytosis to symbiogenesis. Current Biology,
2023 DOI: 10.1016/j.cub.2023.05.020 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230531150117.htm

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