Machanism of iron regulation on amnesic neurontoxin production by coastal diatoms

对一种滨海硅藻伪尼茨奇亚多系进行了批量培养实验，以研究其生长对铁的需求，这种硅藻已知会产生软骨藻酸，一种健忘贝类中毒的致病毒素。当培养基中溶解的无机铁浓度[Fe']约为0/1 nM时，P.multiseries的比生长率下降了50%。与其他沿海浮游植物相似，多叶藻需要较高的溶解无机铁浓度才能最大限度地生长。但P.multiseriesi在[Fe']<0.02 nM时仍能生长，这完全限制了大部分沿海物种的生长。在铁胁迫条件下，添加2μM的软骨藻酸对多刺藻的特定生长速率没有影响，这表明软骨藻酸本身确实刺激了铁的运输，从而支持了高生长速率。当添加真菌铁载体去铁胺B（DFB）大大降低铁的可利用性时，多孢霉的生长速度显著提高。即使在这些严格的铁胁迫条件下，与没有DFB的对照组相比，细胞中的软骨藻酸浓度几乎没有变化。此外，培养基中的软骨藻酸浓度始终低于检测限。这些结果表明，在严重的铁限制条件下，多叶藻可能利用有机配合铁，这种铁运输系统在不产生或释放软骨藻酸的情况下变得活跃。这种铁摄取机制可能使该物种在极低铁条件下生长。

Batch culture experiments were performed to investigate iron requirement for growth of a coastal diatom Pseudo-nitzschia multiseries, which id known to produce domoic acid, a causative toxin of amnestic shellfish poisoning. Specific growth rates of P.multiseries showed a 50% decrease when dissolved inorganic iron concentration [Fe'] in the media was about 0/1 nM. P.multiseriesi required relatively high dissolved inorganic iron concentration for the maximum growth, that is similar to the other coastal phytoplankton. However, P.multiseriesi was still able to grow at [Fe']<0.02 nM, which limit the growth of most coastal species completely. Under iron-stressed condition, specific growth rates of P.multiseriesi were not affected by the addition of 2μM domoic acid, suggesting domoic acid itself does stimulate iron transport to support high growth rates. When iron availability was greatly reduced by the addition of a fungal siderophore desferrioxamine B(DFB), growth rates of P.multiseriesi significantly increased. Even under these strict iron stressed conditions, domoic acid concentrations in the cells showed little change compared with control without DFB. In addition, domoic acid concentrations in the media were always below the detection limit. These findings suggest that P.multiseriesi may utilize organically complexed iron under severe iron limitation and this iron transport system becomes active without production or release of domoic acid. Such iron uptake mechanism may allow this species to grow at the extremely low iron conditions.