Cadmium (Cd) can serve as nutrient in marine diatoms by partially replacing zinc (Zn) in Zn‐limited cells. A major basis for this is the replacement of Cd for Zn in a Cd‐containing carbonic anhydrase (CDCA) needed for cellular acquisition of CO₂. As a result of these interactions, cells can become colimited by Zn, Cd, and CO₂. Large cell size should restrict the cellular uptake of Zn, Cd, and CO₂ due to decreasing surface to volume ratios and limitation of diffusive flux of these nutrients to the cell surface. Large cells are thus more likely to become Zn‐Cd‐CO₂ colimited than smaller ones. These predictions were confirmed in experiments with three marine diatoms: Thalassiosira pseudonana, Thalassiosira weissflogii, and Ditylum brightwellii, ranging in cell volume from 50 to 6000 fL. Cellular Zn : C ratios decreased by 10‐fold between the largest and smallest species, and consequently, the largest diatom was more readily growth‐limited than smaller ones by low external concentrations of bioavailable dissolved inorganic Zn (Zn′). Decreasing cellular Zn : C ratios were accompanied by large increases in cellular Cd uptake rates and Cd : C ratios. However, at the lowest Zn′ concentrations, Cd uptake plateaued, with the larger cells having lower cellular concentrations of both Zn and Cd. Cellular replacement of Zn by Cd was accompanied by increases in cellular CDCA expression. The largest diatom had higher combined carbonic anhydrase activities for a given Zn‐, Cd‐limited growth rate, supporting the hypothesis that these cells could be colimited by Zn, Cd, and CO₂ at low external CO₂ concentrations.

中文翻译：

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细胞大小对海洋硅藻细胞中Zn和Cd以及Zn-Cd-CO2生长速率共限制的影响

镉（Cd）可以通过部分替代锌受限细胞中的锌（Zn）来作为海洋硅藻的营养物质。这样做的主要依据是用细胞吸收CO ₂所需的含镉碳酸酐酶（CDCA）中的Zn替代Cd 。这些相互作用的结果是，细胞可以被Zn，Cd和CO _2限制。大的细胞大小会由于表面积与体积比的降低以及这些营养物向细胞表面的扩散通量的限制而限制细胞对Zn，Cd和CO _2的吸收。因此，大型电池比小型电池更有可能成为Zn-Cd-CO ₂受限的电池。这些预测在以下三个海洋硅藻的实验中得到了证实：Thalassiosira pseudonana，Thalassiosira weissflogii和Ditylum Brightwellii，细胞体积从50到6000 fL。在最大和最小物种之间，细胞的Zn：C比降低了10倍，因此，由于外部可用生物可利用的溶解性无机锌（Zn'）浓度低，最大的硅藻比较小的硅藻更容易受到生长的限制。细胞锌：碳比的降低伴随着细胞镉吸收率和镉：碳比的大幅增加。但是，在最低的Zn'浓度下，Cd吸收达到平台，较大的细胞同时具有较低的Zn和Cd细胞浓度。镉对锌的细胞替代作用伴随着细胞CDCA表达的增加。对于给定的Zn，Cd限制生长速率，最大的硅藻具有更高的联合碳酸酐酶活性，支持以下假设：这些细胞可能被Zn，Cd和CO限制。₂在低外部CO ₂浓度下。