Lis Hagar, Shaked Yeala, Kranzler Chana, Keren Nir, Morel François M M
1] Interuniversity Institute for Marine Sciences, Eilat, Israel [2] The Freddy and Nadine Herrmann Institute of Earth Sciences, Edmond J. Safra Campus, Givat Ram, Hebrew University, Jerusalem, Israel.
1] Interuniversity Institute for Marine Sciences, Eilat, Israel [2] Department of Plant and Environmental Sciences, The Alexander Silberman Institute of Life Sciences, Edmond J. Safra Campus, Givat Ram, Hebrew University, Jerusalem, Israel.
ISME J. 2015 Mar 17;9(4):1003-13. doi: 10.1038/ismej.2014.199.
Phytoplankton are often limited by iron in aquatic environments. Here we examine Fe bioavailability to phytoplankton by analyzing iron uptake from various Fe substrates by several species of phytoplankton grown under conditions of Fe limitation and comparing the measured uptake rate constants (Fe uptake rate/ substrate concentration). When unchelated iron, Fe', buffered by an excess of the chelating agent EDTA is used as the Fe substrate, the uptake rate constants of all the eukaryotic phytoplankton species are tightly correlated and proportional to their respective surface areas (S.A.). The same is true when FeDFB is the substrate, but the corresponding uptake constants are one thousand times smaller than for Fe'. The uptake rate constants for the other substrates we examined fall mostly between the values for Fe' and FeDFB for the same S.A. These two model substrates thus empirically define a bioavailability envelope with Fe' at the upper and FeDFB at the lower limit of iron bioavailability. This envelope provides a convenient framework to compare the relative bioavailabilities of various Fe substrates to eukaryotic phytoplankton and the Fe uptake abilities of different phytoplankton species. Compared with eukaryotic species, cyanobacteria have similar uptake constants for Fe' but lower ones for FeDFB. The unique relationship between the uptake rate constants and the S.A. of phytoplankton species suggests that the uptake rate constant of Fe-limited phytoplankton has reached a universal upper limit and provides insight into the underlying uptake mechanism.
浮游植物在水生环境中常常受到铁的限制。在此，我们通过分析几种在铁限制条件下生长的浮游植物从各种铁底物中摄取铁的情况，并比较所测得的摄取速率常数（铁摄取速率/底物浓度），来研究浮游植物对铁的生物可利用性。当以过量螯合剂乙二胺四乙酸（EDTA）缓冲的未螯合铁Fe²⁺作为铁底物时，所有真核浮游植物物种的摄取速率常数紧密相关，且与其各自的表面积（S.A.）成正比。当以二乙三胺五乙酸铁（FeDFB）作为底物时情况相同，但相应的摄取常数比Fe²⁺的小一千倍。我们所研究的其他底物的摄取速率常数大多介于相同表面积下Fe²⁺和FeDFB的值之间。因此，这两种模型底物从经验上定义了一个生物可利用性范围，Fe²⁺处于铁生物可利用性的上限，FeDFB处于下限。这个范围为比较各种铁底物对真核浮游植物的相对生物可利用性以及不同浮游植物物种的铁摄取能力提供了一个便利的框架。与真核物种相比，蓝细菌对Fe²⁺的摄取常数相似，但对FeDFB的摄取常数较低。浮游植物物种的摄取速率常数与表面积之间的独特关系表明，铁限制条件下浮游植物的摄取速率常数已达到一个普遍的上限，并为潜在的摄取机制提供了见解。
