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An iceberg floats in Antarctica’s cold waters. Credit: Makoto Saito, Woods Hole Oceanographic Institution
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An iceberg floats in Antarctica’s cold waters. Credit: Makoto Saito, Woods Hole Oceanographic Institution
Vitamin B12 deficiency in people can cause various health issues and may even lead to fatality. It was previously believed that the same deficiencies could affect certain types of algae. A recent study has focused on the algae Phaeocystis antarctica’s (P. antarctica) exposure to varying levels of iron and vitamin B12. The results show that this algae has the ability to survive without B12, contrary to what computer analysis of genome sequences had previously suggested.
Originating from the Southern Ocean, this alga begins as a single cell and can grow into millimeter-scale colonies. The research, titled “Flexible B12 ecophysiology of Phaeocystis antarctica due to a fusion B12-independent methionine synthase with widespread homologues,” was published in the Proceedings of the National Academy of Sciences. The study was conducted by researchers from MIT, WHOI, J.C. Venter Institute, and Scripps Institution of Oceanography (UCSD). They found that unlike other important polar phytoplankton, P. antarctica can thrive with or without vitamin B12.
“Vitamin B12 is crucial to the algae’s metabolism because it enables them to produce a key amino acid more efficiently,” stated Makoto Saito, one of the study’s co-authors and a senior scientist at the Woods Hole Oceanographic Institution (WHOI).
“When vitamin B12 is unavailable, life finds ways to produce those amino acids at a slower rate, leading to slower growth. In this case, there are two forms of the enzyme responsible for producing the amino acid methionine – one that requires B12 and another that is slower but does not need B12. This means P. antarctica has the capability to adapt and survive with limited B12 availability.”
Time lapse movie of Phaeocystis antarctica from the Ross Sea . Credit: Makoto Saito, Woods Hole Oceanographic Institution
The researchers reached their conclusions by examining P. antarctica’s proteins in a lab culture, as well as evaluating key proteins in field samples. During their study, they discovered that the algae possesses a B12-independent methionine synthase fusion protein (MetE). While the MetE gene is not new, it was previously thought to be absent in P. antarctica. The presence of MetE gives the algae the flexibility to adjust to low vitamin B12 availability.
“This study indicates that the reality is more complex. For most algae, maintaining a flexible metabolism for B12 is advantageous due to the scarcity of the vitamin in seawater,” explained Deepa Rao, the lead researcher of the study and former MIT postdoc. “Having this flexibility allows them to produce essential amino acids, even when they cannot obtain enough of the vitamin from the environment. This suggests that the classification of algae as B12-requiring or not might be too simplistic.”
P. antarctica, which occupies the base of the food web, was previously believed to be solely influenced by iron nutrition. However, the discovery of the MetE gene suggests that vitamin B12 likely also plays a role. Its presence in P. antarctica provides the algae with a potential advantage to bloom in the early austral spring when the bacteria that produce B12 are less abundant.
Furthermore, this discovery has implications for climate change. The Southern Ocean, where P. antarctica is found, plays a significant role in the Earth’s carbon cycle. P. antarctica absorbs CO2 and releases oxygen through photosynthesis.
Researchers conducting a study of P. Antarctica aboard the R/V Palmer in the Ross Sea. Credit: Makoto Saito
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Researchers conducting a study of P. Antarctica aboard the R/V Palmer in the Ross Sea. Credit: Makoto Saito
“As our global climate warms, there’s increasing amounts of iron entering the coastal Southern Ocean from melting glaciers,” Saito said. “Predicting what the next limiting thing [is] after iron is important, and B12 appears to be one of them. Climate modelers want to know how much algae is growing in the ocean in order to get predictions right and they’ve parameterized iron, but haven’t included B12 in those models yet.”
“We are particularly interested in knowing more about the extent of strain level diversity. It will be interesting to see if B12 independent strains have a competitive advantage in a warmer Southern Ocean,” said co-author of the study Andy Allen, a joint professor at the J. Craig Venter Institute and the Scripps Institution of Oceanography at the University of California, San Diego. “Since there is a cost to B12 independence in terms of metabolic efficiency, an important question is whether or not strains that require B12 might become reliant on B12 producing bacteria.”
The discovery that P. antarctica has the ability to adapt to minimal vitamin B12 availability holds true for many other species of algae that were previously also assumed to be strict B12 users. The findings from this study will pave the way for future research related to the carbon cycle and how different types of algae survive in the Southern Ocean’s cold and harsh environment.
More information:
Deepa Rao et al, Flexible B 12 ecophysiology of Phaeocystis antarctica due to a fusion B 12-independent methionine synthase with widespread homologues, Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2204075121
