Functional Genomics and Phylogenetic Evidence Suggest Genus-Wide Cobalamin Production by the Globally Distributed Marine Nitrogen Fixer Trichodesmium.
Functional Genomics and Phylogenetic Evidence Suggest Genus-Wide Cobalamin Production by the Globally Distributed Marine Nitrogen Fixer Trichodesmium.
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DOI：
10.3389/fmicb.2018.00189
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发表时间：
2018
影响因子：
5.2
通讯作者：
Hutchins DA
中科院分区：
文献类型：
--
作者：
Walworth NG;Lee MD;Suffridge C;Qu P;Fu FX;Saito MA;Webb EA;Sañudo-Wilhelmy SA;Hutchins DA
只有选择的原核生物可以生物合成维生素B12（即，钴），但这些有机辅酶是所有微生物生命所必需的，在广阔的海洋生物群落中可能非常稀少。虽然全球海洋基因组数据表明蓝细菌是钴胺素的主要真光来源，但最近的研究强调，>95%的蓝细菌只能产生钴胺素类似物伪B12，这是由于缺乏合成生物合成钴胺素所需的α配体5，6-二甲基苯并咪唑（DMB）的BluB蛋白。假B12对真核藻类的生物利用率低得多，因为只有某些分类群可以在细胞内将其改造为钴酸盐之一。在这里，我们提出了系统发育，宏基因组学，转录组学，蛋白质组学和化学分析提供多条证据，固氮蓝藻Trichodesmium转录和翻译的生物合成，钴胺素需要BluB酶。系统发育证据表明，束毛藻DMB生物合成基因，bluB，是古老的起源，这可能有助于从其他固氮蓝藻的生态分化。此外，直向同源物分析揭示了两个编码铁依赖性B12生物合成酶（cbiX和isiB）的基因，这表明铁的可用性可能不仅与固氮的新氮供应有关，而且与束毛藻的B12输入有关。这些分析表明，Trichodesmium包含一个以前未被认识到的钴源的作用，这可能会大大影响海洋生物地球化学循环的全属基因组的潜力。
Only select prokaryotes can biosynthesize vitamin B12 (i.e., cobalamins), but these organic co-enzymes are required by all microbial life and can be vanishingly scarce across extensive ocean biomes. Although global ocean genome data suggest cyanobacteria to be a major euphotic source of cobalamins, recent studies have highlighted that >95% of cyanobacteria can only produce a cobalamin analog, pseudo-B12, due to the absence of the BluB protein that synthesizes the α ligand 5,6-dimethylbenzimidizole (DMB) required to biosynthesize cobalamins. Pseudo-B12 is substantially less bioavailable to eukaryotic algae, as only certain taxa can intracellularly remodel it to one of the cobalamins. Here we present phylogenetic, metagenomic, transcriptomic, proteomic, and chemical analyses providing multiple lines of evidence that the nitrogen-fixing cyanobacterium Trichodesmium transcribes and translates the biosynthetic, cobalamin-requiring BluB enzyme. Phylogenetic evidence suggests that the Trichodesmium DMB biosynthesis gene, bluB, is of ancient origin, which could have aided in its ecological differentiation from other nitrogen-fixing cyanobacteria. Additionally, orthologue analyses reveal two genes encoding iron-dependent B12 biosynthetic enzymes (cbiX and isiB), suggesting that iron availability may be linked not only to new nitrogen supplies from nitrogen fixation, but also to B12 inputs by Trichodesmium. These analyses suggest that Trichodesmium contains the genus-wide genomic potential for a previously unrecognized role as a source of cobalamins, which may prove to considerably impact marine biogeochemical cycles.