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Antarctic Algae’s Vitamin B12 Adaptation: Impact on Climate Change and Southern Ocean Life

An iceberg is seen floating in the cold waters of Antarctica. Credit: Makoto Saito, Woods Hole Oceanographic Institution

A deficiency in Vitamin B12 can lead to various health issues and potentially fatal outcomes in humans. Surprisingly, recent research has challenged the conventional belief that such deficiencies only affect specific types of algae. A study focusing on the algae Phaeocystis antarctica (P. antarctica) investigated its response to varying levels of iron and Vitamin B12. The results revealed that this particular algae species can thrive even in the absence of B12, contrary to what genomic analysis had previously suggested.

Originating from the Southern Ocean, P. antarctica begins as a single cell and can later form colonies at the millimeter scale. The research, titled “Flexible B12 ecophysiology of Phaeocystis antarctica due to a fusion B12-independent methionine synthase with widespread homologues,” was conducted by a collaborative team from MIT, WHOI, J.C. Venter Institute, and Scripps Institution of Oceanography (UCSD). It was found that unlike other crucial polar phytoplankton, P. antarctica has the capability to thrive regardless of Vitamin B12 availability.

Makoto Saito, a senior scientist at the Woods Hole Oceanographic Institution (WHOI) and one of the study’s co-authors, emphasized the significance of Vitamin B12 in the algae’s metabolic processes. Saito explained that Vitamin B12 plays a vital role in enhancing the efficiency of amino acid production in the algae. The presence of two forms of the enzyme responsible for amino acid methionine synthesis—one requiring B12 and the other functioning at a slower pace without it—allows P. antarctica to adapt and survive even under low B12 conditions.

The researchers reached their conclusions by analyzing P. antarctica’s proteins in a laboratory setting and examining key proteins in field samples. Their observations led to the discovery of a B12-independent methionine synthase fusion protein (MetE) within the algae. While the MetE gene was not novel, its presence in P. antarctica challenges previous assumptions. This genetic feature equips the algae with the flexibility to adjust to limited Vitamin B12 availability.

Deepa Rao, the lead researcher of the study and a former MIT postdoc, highlighted the complexity of algae metabolism concerning Vitamin B12. Rao pointed out that maintaining a versatile metabolic capability regarding B12 is advantageous for most algae due to the vitamin’s scarcity in seawater. This adaptability enables algae to produce essential amino acids even when B12 is not abundantly available, suggesting that the traditional classification of algae based on B12 requirements may be oversimplified.

Furthermore, the discovery of the MetE gene in P. antarctica implies that Vitamin B12 likely plays a more significant role than previously assumed in the algae’s ecological dynamics. This newfound adaptability gives P. antarctica a potential edge in blooming during the early austral spring when B12-producing bacteria are less prevalent.

The implications of this discovery extend to the broader ecosystem of the Southern Ocean, where P. antarctica thrives and significantly influences the Earth’s carbon cycle. By absorbing CO2 and releasing oxygen through photosynthesis, P. antarctica plays a crucial role in this delicate environmental balance.

“As our global climate warms, there’s increasing amounts of iron entering the coastal Southern Ocean from melting glaciers,” noted Saito. “Predicting what the next limiting factor after iron is crucial, and B12 seems to be one of them. Climate models that aim to forecast algae growth in the ocean have primarily focused on iron, neglecting the role of B12 so far.”

Andy Allen, a co-author of the study and a professor at the J. Craig Venter Institute and the Scripps Institution of Oceanography at the University of California, San Diego, expressed curiosity about the diversity of strains within P. antarctica. Allen raised questions about whether B12-independent strains may gain a competitive advantage in a warmer Southern Ocean environment. He also pondered the possibility of B12-dependent strains becoming reliant on bacteria that produce B12, considering the metabolic efficiency trade-offs associated with B12 independence.

The revelation that P. antarctica can adapt to low Vitamin B12 availability holds true for many other algae species previously believed to be strict B12 dependents. These findings open up avenues for further research on the carbon cycle and the survival strategies of various algae species in the harsh conditions of the Southern Ocean.