Algae acquire vitamin B12 through a symbiotic relationship with bacteria
Algae acquire vitamin B12 through a symbiotic relationship with bacteria
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DOI：
10.1038/nature04056
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发表时间：
2005-11-03
期刊：
影响因子：
64.8
通讯作者：
Smith, AG
中科院分区：
文献类型：
--
作者：
Croft, MT;Lawrence, AD;Smith, AG
维生素B-12（钴胺素）在近80年前被确定为肝脏中的抗恶性贫血因子(1)，其对人类健康和疾病的重要性导致了对其摄取(2)、细胞运输(3)和利用(4)的大量研究。植物不含钴胺素，因为它们没有依赖钴胺素的酶。因此，缺乏叶酸在严格素食者和老年人中很常见(5)，老年人易患自身免疫性疾病，无法有效吸收叶酸(6)。相反，许多藻类富含维生素B-12，一些物种，如紫菜，含有与肝脏一样多的钴胺素。尽管如此，辅助因子在藻类代谢中的作用仍然未知，这些生物维生素的来源也是如此。一项对326种藻类的调查显示，171种藻类的生长需要外源维生素B-12，这意味着超过一半的藻类是钴胺素营养不良者。在这里，我们表明维生素B-12在藻类代谢中的作用主要是作为维生素B-12依赖的蛋氨酸合成酶的辅助因子，并且在整个进化过程中，钴胺素营养不良已经出现了无数次，可能是由于缺乏维生素B-12独立形式的酶。钴胺素的来源似乎是细菌，这表明一种重要的、意想不到的共生关系。
Vitamin B-12 ( cobalamin) was identified nearly 80 years ago as the anti- pernicious anaemia factor in liver(1), and its importance in human health and disease has resulted in much work on its uptake(2), cellular transport(3) and utilization(4). Plants do not contain cobalamin because they have no cobalamin-dependent enzymes. Deficiencies are therefore common in strict vegetarians(5), and in the elderly, who are susceptible to an autoimmune disorder that prevents its efficient uptake(6). In contrast, many algae are rich in vitamin B-12, with some species, such as Porphyra yezoensis (Nori), containing as much cobalamin as liver(7). Despite this, the role of the cofactor in algal metabolism remains unknown, as does the source of the vitamin for these organisms. A survey of 326 algal species revealed that 171 species require exogenous vitamin B-12 for growth, implying that more than half of the algal kingdom are cobalamin auxotrophs. Here we show that the role of vitamin B-12 in algal metabolism is primarily as a cofactor for vitamin B-12-dependent methionine synthase, and that cobalamin auxotrophy has arisen numerous times throughout evolution, probably owing to the loss of the vitamin B-12-independent form of the enzyme. The source of cobalamin seems to be bacteria, indicating an important and unsuspected symbiosis.