New microbial species can capture carbon

Australian scientists have described a new species of carbon-capturing microbe living in waters near Sydney.

The study published in Nature Communications offers new insight into the ocean’s carbon cycles, and may even hold hope for a novel nature-inspired method of carbon capture to help combat climate change.

The microbe, called Prorocentrum cf. balticum, is not a bacterium but a member of a relatively little-known branch of the tree of life: the protists. Protists are eukaryotes, meaning they have a distinct nucleus and organelles inside their cells, but don’t fit into the kingdoms of animals, plants or fungi.

These mostly single-celled creatures are quite common in the ocean, but we don’t understand a lot about what they do there. P. cf. balticum is a mixotroph, which means it can photosynthesise like a plant and also consume other organisms like an animal.

Michaela Larsson, a marine biologist at University of Technology Sydney (UTS) who led the paper, describes the microbe as analogous to a carnivorous plant.

“Most terrestrial plants use nutrients from the soil to grow, but some, like the Venus flytrap, gain additional nutrients by catching and consuming insects,” she says.

“Similarly, marine microbes that photosynthesise, known as phytoplankton, use nutrients dissolved in the surrounding seawater to grow.

“However, our study organism, Prorocentrum cf. balticum, is a mixotroph, so is also able to eat other microbes for a concentrated hit of nutrients, like taking a multivitamin.”

This flexible dietary strategy helps the microbe survive in parts of the ocean where phytoplankton can’t. But that’s not the only cool trick Prorocentrum cf. balticum has up its sleeve. Its method for capturing its occasional prey actually helps to also capture carbon too.

The UTS researchers discovered that the microbe uses the carbon it gets from photosynthesis to build a three-dimensional carbon-rich structure out of mucus, which they dubbed a “mucosphere”.

Carbon capture concept illustration of the mucosphere housing the protist with prey microbes stuck in the mucus
An artist’s impression of the mucosphere housing P. cf. balticum and trapping microscopic prey. Credit: Larsson et al (2022) / Martina Doblin via Twitter.

The mucosphere acts a bit like a spider’s web – it traps the microbe’s prey to be eaten at leisure. On top of this, the mucosphere actually emits chemicals that attract prey to the ‘web’.

After the mucosphere has successfully caught enough prey to satisfy P. cf. balticum, it is abandoned and sinks through the water, taking its trapped carbon with it.

“This is an entirely new species, never before described in this amount of detail,” says senior author Martina Doblin, a professor at UTS.

“The implication is that there’s potentially more carbon sinking in the ocean than we currently think.”

Importantly, the mucospheres can still be made under nutrient-deficient ocean conditions – which are what we’ll see more of under current climate change trends.

Doblin says that the next step will be to learn more about how fast the mucospheres sink and whether they are broken down by marine bacteria, which would likely release the carbon again.

“This could be a game changer in the way we think about carbon and the way it moves in the marine environment,” she says.

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