Global Concerns with B Vitamin Statuses: Biofortification,Fortification, Hidden Hunger,Interactions, and Toxicity

The prevalence of undernutrition due to insufficient energy intake has been reduced by nearly 50% since 1990. This reduction is largely attributed to improved yields of staple crops, such as wheat, rice, and maize; however, these improvements did little for micronutrient deficiencies that affect an estimated two billion people worldwide. Starchy staple crops are energy dense but are often lacking in one or more B vitamins, making resource‐constrained people who consume monotonous diets comprised predominantly of these staples at risk for developing deficiency. B vitamin deficiencies occur due to a poor overall nondiversified diet and rarely occur alone. Many B vitamins are essential cofactors involved in the metabolism of other nutrients, including other B vitamins, whereby the deficiency of one B vitamin affects the metabolism and status measurements of another. Food fortification efforts have nearly eradicated diseases of extreme B vitamin deficiency, such as beriberi from thiamin deficiency and pellagra from niacin deficiency. However, subclinical deficiency, sometimes referred to as hidden hunger, is still common especially in low‐income countries. Most dietary B vitamins, due to their water‐soluble nature, are not a concern for excessive intakes, but synthetic forms used for fortification and supplements sometimes can have adverse effects when consumed in high amounts. Biofortified crops offer a long‐term sustainable method to increase the amount of dietary B vitamins for people who rely on staple crops for most of their caloric intake. Efforts have been made to improve B vitamin content of crops, especially for thiamin, vitamin B₆, and folate, but none have undergone human feeding trials; therefore, more research is needed to provide sustainable and scalable solutions in many parts of the world.     

Comparison of the chemical properties of iron and cobalt porphyrins and corrins

Density functional calculations have been used to compare various geometric, electronic and functional properties of iron and cobalt porphyrin (Por) and corrin (Cor) species. The investigation is focussed on octahedral M(II/III) complexes (where M is the metal) with two axial imidazole ligands (as a model of b and c type cytochromes) or with one imidazole and one methyl ligand (as a model of methylcobalamin). However, we have also studied some five-coordinate M(II) complexes with an imidazole ligand and four-coordinate M(I/II) complexes without any axial ligands as models of other intermediates in the reaction cycle of coenzyme B12. The central cavity of the corrin ring is smaller than that of porphine. We show that the cavity of corrin is close to ideal for low-spin Co(III), Co(II), and Co(I) with the axial ligands encountered in biology, whereas the cavity in porphine is better suited for intermediate-spin states. Therefore, the low-spin state of Co is strongly favoured in complexes with corrins, whereas there is a small energy difference between the various spin states in iron porphyrin species. There are no clear differences for the reduction potentials of the octahedral complexes, but [Co(I)Cor] is more easily formed (by at least 40 kJ mole(-1)) than [Fe(I)Por]. Cobalt and corrin form a strong Cobond;C bond that is more stable against hydrolysis than iron and porphine. Finally, Fe(II/III) gives a much lower reorganisation energy than Co(II/III); this is owing to the occupied d(z2) orbital in Co(II). Altogether, these results give some clues about how nature has chosen the tetrapyrrole rings and their central metal ion.     

维生素B_(12)的生物合成研究

维生素B12广泛应用于医药、食品和畜牧业,主要由微生物发酵得到。脱氮假单胞菌(Pseudomonas denitrificans)和费氏丙酸杆菌(Propionibacterium freudenreichii)是主要的生产菌种。与之相应,维生素B12存在好氧和厌氧2条生物合成途径,生物合成过程十分复杂,2条合成途径大体相同又各有特点。维生素B12发酵产量的提高有待于菌种的改良和发酵工艺的改进。了解维生素B12生物合成途径和代谢调控机制具有重要意义,可为育种工作提供理论基础。     

不同钴胺素对其检测菌生长速度的影响

以氰钴胺、甲钴胺和腺苷钴胺的水溶液对维生素B12的缺陷菌——德氏乳酸杆菌（Lactobacillus delbrueckiiATCC 7830）进行刺激生长试验,证明出不同钴胺素对该种细菌生长速度的影响不同。     

一种简便、快速测定发酵液中V_(B_(12))含量的方法

文中探索了一种不经氰化物转化而直接使用HPLC测定发酵液中维生素B12 (包括羟基钴胺素、脱氧腺苷钴胺素和甲基钴胺素 )的检测方法。将发酵液离心取菌体 ,样品预处理后进样分析 ,采用乙腈和醋酸钠缓冲液为流动相。此方法能够精确检测上述 3种钴胺素 ,并且重复性好、分析速度快 ,可应用于工业发酵生产维生素B12 的过程监控和检测。     

Microbial and Genetic Resources for Cobalamin (Vitamin B12) Biosynthesis: From Ecosystems to Industrial Biotechnology

Many microbial producers of coenzyme B12 family cofactors together with their metabolically interdependent pathways are comprehensively studied and successfully used both in natural ecosystems dominated by auxotrophs, including bacteria and mammals, and in the safe industrial production of vitamin B12. Metabolic reconstruction for genomic and metagenomic data and functional genomics continue to mine the microbial and genetic resources for biosynthesis of the vital vitamin B12. Availability of metabolic engineering techniques and usage of affordable and renewable sources allowed improving bioprocess of vitamins, providing a positive impact on both economics and environment. The commercial production of vitamin B12 is mainly achieved through the use of the two major industrial strains, Propionobacterium shermanii and Pseudomonas denitrificans, that involves about 30 enzymatic steps in the biosynthesis of cobalamin and completely replaces chemical synthesis. However, there are still unresolved issues in cobalamin biosynthesis that need to be elucidated for future bioprocess improvements. In the present work, we review the current state of development and challenges for cobalamin (vitamin B12) biosynthesis, describing the major and novel prospective strains, and the studies of environmental factors and genetic tools effecting on the fermentation process are reported.