Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL, 60201, United States of America.
Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2 PB, United Kingdom.
Acta Biomater. 2021 Apr 15;125:83-89. doi: 10.1016/j.actbio.2021.02.025. Epub 2021 Feb 22.
The localization of organic material within biominerals is central to developing biomineral formation mechanisms. Coccoliths, morphologically sophisticated calcite platelets of intracellularly calcifying coccolithophores, are not only eco-physiologically important, but also influence biogeochemical cycles through mass production. Despite their importance and over a century of research, the formation mechanism of coccoliths is still poorly understood. Crucial unsolved questions include the localization of organic material within coccoliths. In extracellular calcifiers the discovery of an organics-containing nano-structure within seemingly single crystals has led to the formulation of a two-step crystallization mechanism. Coccoliths are traditionally thought of as being formed by a different mechanism, but it is unclear whether coccolith crystals possess a nano-structure. Here we review the evidence for and against such a nano-structure. Current SXPD analyses suggest a nano-structure of some kind, while imaging methods (SEM, TEM, AFM) provide evidence against it. We suggest directions for future research which should help solve this puzzle. STATEMENT OF SIGNIFICANCE: Coccolithophores, unicellular calcifying algae, are important primary producers and contribute significantly to pelagic calcium carbonate export. Their calcite platelets, the coccoliths, are amongst the most sophisticated biomineral structures. Understanding the crystallization mechanism of coccolith crystals is not only central to coccolithophore cell biology but also lies at the heart of biomineralization research more generally. The crystallization mechanism of coccoliths has remained largely elusive, not least because it is still an open question whether the micron sized coccolith crystals are pure calcite, or contain organic material. Here we review the state of the art and suggest a way to solve this central problem.
有机物质在生物矿物中的定位对于开发生物矿物形成机制至关重要。 球石藻的细胞内钙化球石是形态复杂的方解石薄片，不仅在生态生理学上很重要，而且通过大规模生产还影响生物地球化学循环。 尽管它们很重要，并且已经研究了一个多世纪，但球石的形成机制仍未得到很好的理解。 关键的未解决问题包括有机物质在球石中的定位。 在细胞外钙化剂中，在看似单晶内发现含有有机物的纳米结构，导致提出了两步结晶机制。 球石传统上被认为是通过不同的机制形成的，但是否球石晶体具有纳米结构尚不清楚。 在这里，我们回顾了支持和反对这种纳米结构的证据。 当前的 SXPD 分析表明存在某种纳米结构，而成像方法（SEM，TEM，AFM）则提供了反对的证据。 我们提出了未来研究的方向，这应该有助于解决这个难题。 意义声明：单细胞钙化藻类球石藻是重要的初级生产者，对浮游碳酸钙的输出有重要贡献。 它们的方解石薄片，即球石，是最复杂的生物矿物结构之一。 了解球石晶体的结晶机制不仅是球石藻细胞生物学的核心，而且更广泛地说是生物矿化研究的核心。 球石晶体的结晶机制仍然很大程度上难以捉摸，尤其是因为微米大小的球石晶体是否是纯方解石，还是含有有机物质，这仍然是一个悬而未决的问题。 在这里，我们回顾了现状，并提出了解决这一核心问题的方法。
