Competitive inhibition of cobalt uptake by zinc and manganese in a pacific Prochlorococcus strain: Insights into metal homeostasis in a streamlined oligotrophic cyanobacterium
Competitive inhibition of cobalt uptake by zinc and manganese in a pacific Prochlorococcus strain: Insights into metal homeostasis in a streamlined oligotrophic cyanobacterium
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DOI：
10.1002/lno.10935
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发表时间：
2018-09-01
影响因子：
4.5
通讯作者：
Saito, Mak A.
中科院分区：
文献类型：
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作者：
Hawco, Nicholas J.;Saito, Mak A.
为了满足生长的代谢需求，海洋蓝藻如原绿球藻必须从海水中获取钴并合成钴胺素辅助因子。通过在钴限制条件下对原绿球菌菌株MIT 9215进行一系列实验，研究了原绿球菌吸收钴的机制。由于配额较低，原绿球藻 MIT 9215 可以以极慢的钴吸收速度（每个细胞每小时大约 1 个原子）保持生长。钴配额与无机钴物质 Co 的浓度呈线性相关，表明转运蛋白上的金属结合位点对于钴而言是高度不饱和的。当受到钴的限制时，原绿球藻的生长速率在高水平的锌和锰下下降，表明这两种金属与钴竞争相同的转运蛋白。在大范围的铁、铜和镍浓度下没有观察到这种效应，尽管在高镍浓度下指数生长的开始被延迟。这些观察结果与周质锰结合蛋白 MntC 的先前表征一致，MntC 可能是无机钴吸收的主要途径以及锰和锌竞争性抑制的位点。锌对钴限制原绿球藻 MIT 9215 的毒性与在真核浮游植物中观察到的钴-锌替代物形成对比，并且预计会在与环境相关的游离锌和钴离子浓度下发生。因此，原绿球藻在现代海洋中的生态成功可能取决于能否获得由强有机配体络合的钴，而这些有机配体不受其他金属的竞争性抑制。
In order to satisfy metabolic requirements for growth, marine cyanobacteria such as Prochlorococcus must acquire cobalt from seawater and synthesize cobalamin cofactors. Through a series of experiments with Prochlorococcus strain MIT 9215 under cobalt limiting conditions, the mechanism of Prochlorococcus' cobalt uptake was investigated. Due to low quotas, Prochlorococcus MIT 9215 can maintain growth at extremely slow rates of cobalt uptake, circa 1 atom per cell per hour. Cobalt quotas were linearly related to the concentration of inorganic cobalt species, Co, indicating that the metal binding sites on the transporter are strongly unsaturated with respect to cobalt. When limited by cobalt, Prochlorococcus growth rates decreased at high levels of both Zn and Mn, suggesting that both metals compete with cobalt for the same transporter. This effect was not observed under a wide range of Fe, Cu, and Ni concentrations, although the onset of exponential growth was delayed at high Ni. These observations agree with prior characterizations of the periplasmic manganese binding protein MntC, which is probably the main pathway for inorganic cobalt uptake and the locus for Mn and Zn competitive inhibition. The toxicity of zinc toward cobalt limited Prochlorococcus MIT 9215 contrasts with the observation of cobalt-zinc substitution in eukaryotic phytoplankton and is expected to occur at environmentally relevant concentrations of free zinc and cobalt ions. Thus, the ecological success of Prochlorococcus in the modern ocean may depend on access to cobalt complexed by strong organic ligands that are not subject to competitive inhibition by other metals.