Did you know that the GREEN sheets used to wrapsushi are made from RED algae?
This week’s leaf is for plant lovers, orrather, those who eschew animal products in their diet. You have probably beentold that plants completely lack vitamin B₁₂ supplement, so you MUST take asupplement or eat products enriched with manufactured B₁₂.
Vitamin B₁₂ (cobalamin) is an essential “coenzyme” in animal metabolism, required for several enzymes needed for amino-acids and fatty acids, and for DNA synthesis. These are essential metabolic pathways in all lifeforms, so how do other organisms survive?
Cobalamin is a corrinoid molecule with a squarish central skeleton (see picture) similar to other “tetrapyrrole” molecules like haem and chlorophyll. A prominent difference is the central Cobalt ion (Co³⁺),rather than magnesium in chlorophyll or iron in haem. Cobalamin, however, is synthesised only by bacteria and archaea, and from there finds its way through the food chain to other. Most herbivores get enough B₁₂ from their but microbiomes; cows get it from bacterial fermentation in their rumens. Human gut bacteria also make some cobalamin, but it is poorly absorbed.
What about plants? Land plants have alternativeenzymes that work without cobalamin. They don’t need cobalamin and they don’t synthesise it, though some plants can accumulate measurable amounts produced by bacteriain their rhizosphere. Aqueous plant life, however, is a different story. Manyspecies of eukaryotic algae have an absolute requirement for cobalamin, and seemto get it by importing and modifying corrinoids produced by cohabitingprokaryotic cyanobacteria.
The rhodophyta (red algae) are a phylogenetic division distinct from the chlorophyta division that contains land plants and green algae. Despite the name, the rhodophytes have green chlorophyll, but like cyanobacteria they have phycobiliproteins as photosynthetic accessory pigments. The rhodophyte seaweed Pyropia is edible, notably in Welsh laverbread and Nori that wraps Japanese sushi. The good news for vegans is that Pyropia a good source of vitamin B₁₂.what
References
💊 Helliwell KE et al (2016). Cyanobacteria and Eukaryotic Algae Use Different Chemical Variants of Vitamin B12. Current biology : CB, 26(8),999–1008. https://doi.org/10.1016/j.cub.2016.02.041
💊 Watanabe F et al (2014). Vitamin B₁₂-containing plant food sources for vegetarians. Nutrients, 6(5), 1861–1873. https://doi.org/10.3390/nu6051861
💊 Wikipedia (2024). Nori. https://en.wikipedia.org/w/index.php?title=Nori&oldid=1216140141
