Department of Botany, National Museum of Nature and Science, Tsukuba 305-0005, Japan.
Graduate School of Natural Science, Konan University, Kobe 658-8501, Japan; Institute for Integrative Neurobiology, Konan University, Kobe 658-8501, Japan.
J Struct Biol. 2018 Oct;204(1):45-51. doi: 10.1016/j.jsb.2018.06.008. Epub 2018 Jul 3.
Cross-sections were prepared by ultramicrotome (UM) and focused ion beam (FIB) system in order to examine the skeletal structure of ecologically and geologically important shell-bearing protists: phaeodarians and radiolarians. The elemental composition of the skeleton was clarified by the energy dispersive X-ray spectroscopy, suggesting that the skeletons of both groups are mainly made of amorphous silica (SiO·nHO) with other minor elements (Na, Mg, Al, Cl, K, Ca and Fe) and that these two groups have similar elemental composition, compared with other siliceous organisms (diatoms and sponges). However, the structural difference among the two groups was confirmed: phaeodarian skeletons are porous, unlike radiolarians with solid skeletons. It was also revealed that the phaeodarian skeleton contains concentric layered structure with spaces, presumably related to the ontogenetic skeleton formation. The distinction in the skeletal ultrafine structure (porous/solid and non-dense/dense) would reflect the ecological difference among the two groups and could be an effective criterion to determine whether microfossils belong to Radiolaria or Phaeodaria. The UM and FIB combined method presented in this study could be a useful approach to examine the chemical and structural characteristics of unculturable and/or rare microorganisms.
为了研究具有生态和地质重要性的带壳原生生物（如颗石藻和放射虫）的骨骼结构，我们通过超微切片机（UM）和聚焦离子束（FIB）系统制备了切片。通过能谱分析澄清了骨骼的元素组成，表明这两组的骨骼主要由无定形二氧化硅（SiO·nHO）组成，还有其他少量元素（Na、Mg、Al、Cl、K、Ca 和 Fe），与其他硅质生物（如硅藻和海绵）相比，这两组的元素组成相似。然而，两组之间的结构差异得到了证实：颗石藻的骨骼是多孔的，而放射虫的骨骼是实心的。研究还表明，颗石藻的骨骼具有同心层状结构和空间，可能与个体发生骨骼形成有关。骨骼超微结构的差异（多孔/实心和非致密/致密）反映了两组之间的生态差异，可能是确定微化石属于放射虫目还是颗石藻目的有效标准。本研究中提出的 UM 和 FIB 联合方法可能是一种有用的方法，可以研究不可培养和/或稀有微生物的化学和结构特征。
