Bioavailability of mineral‐associated trace metals as cofactors for nitrogen fixation by Azotobacter vinelandii
Bioavailability of mineral‐associated trace metals as cofactors for nitrogen fixation by Azotobacter vinelandii
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DOI：
10.1111/gbi.12552
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发表时间：
2023-02
期刊：
影响因子：
3.7
通讯作者：
S. Srivastava;Hailiang Dong;O. Baars;Yizhi Sheng
中科院分区：
文献类型：
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作者：
S. Srivastava;Hailiang Dong;O. Baars;Yizhi Sheng
地球上的生命依赖于固氮微生物通过固氮酶从大气中的N2气体中制造氨。大多数固氮酶使用Mo作为辅因子;然而，V和Fe也是可能的。N2固定曾经被认为是在太古宙-元古代使用Fe作为辅助因子进化而来的。然而，古海洋沉积物的δ 15 N值表明Mo和V辅因子，尽管它们在古海洋中的浓度较低。这一明显的悖论是基于一个未经检验的假设，即只有可溶性金属是生物可利用的。在这项研究中，进行了实验室实验，以测试矿物相关的微量金属的生物利用度的模式固氮菌棕色固氮菌。N2固定时，观察钼在钙钛矿，钒在钙钛矿，和铁的水铁矿作为唯一的来源的辅因子，但N2固定率大大降低。矿物质和细胞之间的物理分离进一步降低了N2固定率。生化分析检测到五种铁载体，包括氨基螯合素，azotochelin，azotochelin肌动蛋白，原螯合素，和弧菌铁蛋白，作为可能的螯合剂，从矿物中提取金属。这项研究的结果表明，矿物相关的微量金属是生物可利用的固氮酶的辅因子，以支持N2固定在那些缺乏可溶性微量金属的环境中，并可能提供一个部分答案的悖论。
Life on Earth depends on N2‐fixing microbes to make ammonia from atmospheric N2 gas by the nitrogenase enzyme. Most nitrogenases use Mo as a cofactor; however, V and Fe are also possible. N2 fixation was once believed to have evolved during the Archean‐Proterozoic times using Fe as a cofactor. However, δ15N values of paleo‐ocean sediments suggest Mo and V cofactors despite their low concentrations in the paleo‐oceans. This apparent paradox is based on an untested assumption that only soluble metals are bioavailable. In this study, laboratory experiments were performed to test the bioavailability of mineral‐associated trace metals to a model N2‐fixing bacterium Azotobacter vinelandii. N2 fixation was observed when Mo in molybdenite, V in cavansite, and Fe in ferrihydrite were used as the sole sources of cofactors, but the rate of N2 fixation was greatly reduced. A physical separation between minerals and cells further reduced the rate of N2 fixation. Biochemical assays detected five siderophores, including aminochelin, azotochelin, azotobactin, protochelin, and vibrioferrin, as possible chelators to extract metals from minerals. The results of this study demonstrate that mineral‐associated trace metals are bioavailable as cofactors of nitrogenases to support N2 fixation in those environments that lack soluble trace metals and may offer a partial answer to the paradox.