Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic.
Faculty of Science, Charles University, Prague, Czech Republic.
mBio. 2023 Feb 28;14(1):e0327922. doi: 10.1128/mbio.03279-22. Epub 2023 Jan 16.
Barium and strontium are often used as proxies of marine productivity in palaeoceanographic reconstructions of global climate. However, long-searched biological drivers for such correlations remain unknown. Here, we report that taxa within one of the most abundant groups of marine planktonic protists, diplonemids (Euglenozoa), are potent accumulators of intracellular barite (BaSO), celestite (SrSO), and strontiobarite (Ba,Sr)SO. In culture, accumulates Ba and Sr 42,000 and 10,000 times higher than the surrounding medium, forming barite and celestite representing 90% of the dry weight, the greatest concentration in biomass known to date. As heterotrophs, diplonemids are not restricted to the photic zone, and they are widespread in the oceans in astonishing abundance and diversity, as their distribution correlates with environmental particulate barite and celestite, prevailing in the mesopelagic zone. We found diplonemid predators, the filter-feeding zooplankton that produces fecal pellets containing the undigested celestite from diplonemids, facilitating its deposition on the seafloor. To the best of our knowledge, evidence for diplonemid biomineralization presents the strongest explanation for the occurrence of particulate barite and celestite in the marine environment. Both structures of the crystals and their variable chemical compositions found in diplonemids fit the properties of environmentally sampled particulate barite and celestite. Finally, we propose that diplonemids, which emerged during the Neoproterozoic era, qualify as impactful players in Ba/Sr cycling in the ocean that has possibly contributed to sedimentary rock formation over long geological periods. We have identified that diplonemids, an abundant group of marine planktonic protists, accumulate conspicuous amounts of Sr and Ba in the form of intracellular barite and celestite crystals, in concentrations that greatly exceed those of the most efficient Ba/Sr-accumulating organisms known to date. We propose that diplonemids are potential players in Ba/Sr cycling in the ocean and have possibly contributed to sedimentary rock formation over long geological periods. These organisms emerged during the Neoproterozoic era (590 to 900 million years ago), prior to known coccolithophore carbonate biomineralization (~200 million years ago). Based on reported data, the distribution of diplonemids in the oceans is correlated with the occurrence of particulate barite and celestite. Finally, diplonemids may provide new insights into the long-questioned biogenic origin of particulate barite and celestite and bring more understanding of the observed spatial-temporal correlation of the minerals with marine productivity used in reconstructions of past global climate.
钡和锶常被用作古海洋学中全球气候重建的海洋生产力的代用指标。然而，长期以来，这种相关性的生物学驱动因素仍不清楚。在这里，我们报告说，在海洋浮游原生生物中最丰富的群体之一的双滴虫（Euglenozoa）中，某些分类群是细胞内重晶石（BaSO）、天青石（SrSO）和锶钡矿（Ba，Sr）SO 的有力积累者。在培养中， 积累的 Ba 和 Sr 分别比周围介质高 42,000 和 10,000 倍，形成重晶石和天青石，占干重的 90%，这是迄今为止已知的生物质中最高的浓度。作为异养生物，双滴虫不限于光区，它们在海洋中分布广泛，数量惊人，多样性丰富，因为它们的分布与中海洋层中普遍存在的环境颗粒重晶石和天青石相关。我们发现了双滴虫的捕食者，即滤食性浮游动物，它们产生含有双滴虫未消化的天青石的粪便颗粒，促进了天青石在海底的沉积。据我们所知，双滴虫生物矿化的证据为海洋环境中颗粒重晶石和天青石的存在提供了最强的解释。在双滴虫中发现的晶体结构及其可变的化学成分与环境采样的颗粒重晶石和天青石的性质相吻合。最后，我们提出，在新元古代出现的双滴虫，作为海洋中钡/锶循环的有影响力的参与者，可能有助于长期地质时期的沉积岩形成。我们已经确定，海洋浮游原生生物中丰富的双滴虫群体以细胞内重晶石和天青石晶体的形式积累大量的 Sr 和 Ba，其浓度远远超过迄今为止已知的最有效的钡/锶积累生物。我们提出，双滴虫可能是海洋钡/锶循环的潜在参与者，并可能在长期地质时期有助于沉积岩的形成。这些生物出现在新元古代（5.9 亿至 9 亿年前），早于已知的颗石藻碳酸盐生物矿化作用（约 2 亿年前）。根据报告的数据，双滴虫在海洋中的分布与颗粒重晶石和天青石的存在相关。最后，双滴虫可能为长期存在争议的颗粒重晶石和天青石的生物起源提供新的见解，并更好地理解在过去全球气候重建中观察到的与海洋生产力的矿物的时空相关性。
