University of Bristol, School of Earth Sciences, Wills Memorial Building, Queen's Road, Brsitol, BS8 1RJ, UK.
University of Bristol, School of Biochemistry, Medical Sciences Building, University Walk, Bristol, BS8 1TD, UK.
Sci Rep. 2021 May 6;11(1):9698. doi: 10.1038/s41598-021-88881-6.
The stable isotopic composition of diatom silica is used as a proxy for nutrient utilisation in natural waters. This approach provides essential insight into the current and historic links between biological production, carbon cycling and climate. However, estimates of isotopic fractionation during diatom silica production from both laboratory and field studies are variable, and the biochemical pathways responsible remain unknown. Here, we investigate silicon isotopic fractionation through a series of chemical precipitation experiments that are analogous to the first stages of intracellular silica formation within the diatom silicon deposition vesicle. The novelty of our experiment is the inclusion of the R5 peptide, which is closely related to a natural biomolecule known to play a role in diatom silicification. Our results suggest that the presence of R5 induces a systematic but non-significant difference in fractionation behaviour. It thus appears that silicon isotopic fractionation in vitro is largely driven by an early kinetic fractionation during rapid precipitation that correlates with the initial amount of dissolved silica in the system. Our findings raise the question of how environmental changes might impact silicon isotopic fractionation in diatoms, and whether frustule archives record information in addition to silica consumption in surface water.
硅藻二氧化硅的稳定同位素组成被用作天然水中营养物质利用的示踪剂。这种方法为当前和历史上生物生产力、碳循环和气候之间的联系提供了重要的见解。然而，实验室和野外研究中对硅藻二氧化硅生产过程中同位素分馏的估计是可变的，其负责的生化途径仍然未知。在这里，我们通过一系列化学沉淀实验来研究硅同位素分馏，这些实验类似于硅藻硅沉积囊泡内细胞内二氧化硅形成的早期阶段。我们实验的新颖之处在于包含 R5 肽，它与一种已知在硅藻硅化中起作用的天然生物分子密切相关。我们的结果表明，R5 的存在诱导了分馏行为的系统但非显著差异。因此，体外硅同位素分馏主要是由快速沉淀过程中的早期动力学分馏驱动的，这与系统中溶解二氧化硅的初始量相关。我们的研究结果提出了这样一个问题，即环境变化可能如何影响硅藻中的硅同位素分馏，以及是否贝壳记录的信息除了地表水的硅消耗之外还有其他信息。
