Section 3.3, Earth Surface Geochemistry, GFZ German Research Centre for Geosciences , Telegrafenberg, 14473 Potsdam, Germany.
Institute of Geological Sciences, Freie Universität Berlin , 12249 Berlin, Germany.
Environ Sci Technol. 2017 Sep 5;51(17):9691-9699. doi: 10.1021/acs.est.7b01798. Epub 2017 Aug 18.
The model rock-inhabiting microcolonial fungus Knufia petricola fractionates stable Mg isotopes in a time- and pH-dependent manner. During growth, the increase of Mg/Mg in the fungal cells relative to the growth media amounted to 0.65 ± 0.14‰ at pH 6 and 1.11 ± 0.35‰ at pH 3. We suggest a constant equilibrium fractionation factor during incorporation of Mg into ribosomes and ATP as a cause of enrichment of Mg in the cells. We suggest too that the proton gradient across the cell wall and cytoplasmic membrane controls Mg transport into the fungal cell. As the strength of this gradient is a function of extracellular solution pH, the pH-dependence on Mg isotope fractionation is thus due to differences in fungal cell mass fluxes. Through a mass balance model we show that Mg uptake into the fungal cell is not associated with a unique Mg isotope fractionation factor. This Mg isotope fractionation dependence on pH might also be observed in any organism with cells that follow similar Mg uptake and metabolic pathways and serves to reveal Mg cycling in ecosystems.
模式岩石栖息的微型殖民地真菌 Knufia petricola 以时间和 pH 值依赖的方式分离稳定的镁同位素。在生长过程中，相对于生长介质，真菌细胞中 Mg/Mg 的增加量在 pH 值为 6 时达到 0.65±0.14‰，在 pH 值为 3 时达到 1.11±0.35‰。我们认为，在将镁掺入核糖体和 ATP 中的过程中，镁的平衡常数同位素分馏因子是导致细胞中镁富集的原因。我们还认为，穿过细胞壁和细胞质膜的质子梯度控制着镁向真菌细胞的运输。由于该梯度的强度是细胞外溶液 pH 值的函数，因此 pH 值对镁同位素分馏的依赖性是由于真菌细胞质量通量的差异造成的。通过质量平衡模型，我们表明，镁进入真菌细胞与独特的镁同位素分馏因子无关。这种 pH 值依赖的镁同位素分馏也可能在任何具有类似镁吸收和代谢途径的细胞的生物体中观察到，并有助于揭示生态系统中的镁循环。
