A study on the mechanism of domoic acid production by a pennate diatom.

关于多系列藻软骨藻酸的产生机制，提出了一种假说，认为软骨藻酸的产生可能是由于藻类细胞异养摄取细菌或某些细菌产物的结果。为了阐明这一假说，我们首先对软骨藻的产酸、光合作用、铁吸收和细菌共存进行了一些培养实验。测定了多系假凤尾藻非无菌培养和无菌培养的软骨藻酸和溶铁浓度。在非无菌培养中，溶解铁耗尽后，软骨藻酸开始大量生产。然而，在无菌培养的情况下，溶解铁耗尽10天后，软骨藻酸的产量很低，这表明软骨藻酸的产生不仅与溶解铁的消耗有关，而且与细菌的共存有关。在无菌培养的情况下，少量细菌可能在藻类细胞内存活，并可能帮助产生软骨藻酸。细菌对P. multiseries产软骨藻酸的影响受到正常透析膜（m.w. 12,000切断）的干扰，而0.2 μm膜过滤器没有干扰，这表明细菌对软骨藻酸的影响不需要细菌和藻类直接接触。在黑暗条件下，非无菌P.多系列培养中软骨藻酸的产生停止，并且通过添加30 μM的ATP、NADP、NADPH和葡萄糖不能恢复。这些结果表明，多系软骨藻酸的产生可能与溶解铁的耗竭和一些细菌产物与铁的螯合有关，然后在光合作用下被藻类细胞吸收。

Regarding the domoic acid production mechanism of P. multiseries, a hypothesis was made that domoic acid production might be occurred as a result of a heterotrophic uptake of bacteria or some bacterial products by algal cells. In order to clarify this hypothesis, a few culture experiments were primarily performed concerning the domoic acid production comparing with its photosynthesis, iron uptake and bacterial co-existence. Determination of the non-axenic and axenic culture of P. multiseries was done for both domoic acid and dissolved iron concentration. Significant amount of domoic acid production was started just after the depletion of dissolved iron in non-axenic culture. However, in case of axenic culture, just a low level of domoic acid production was observed 10 days after the depletion of dissolved iron, This results suggest that domoic acid production occurs not only in association with dissolved iron depletion but also with the co-existence of bacteria. In case of axenic culture, small number of bacteria might be alive inside the algal cells and might help producing domoic acid. The influence of bacteria on the production of domoic acid by P. multiseries was disturbed by a normal dialyzing membrane (m.w. 12,000 cut off), however it was not disturbed by a 0.2 μm membrane filter, suggesting that the bacterial effect on the domoic acid production does not need direct contact between bacteria and algae. Domoic acid production in non-axenic P. multiseries culture was stopped under dark conditions and was not recovered by adding 30 μM ATP, NADP, NADPH, and glucose. These results suggest that domoic acid production of P. multiseries might be occurred in association with depletion of dissolved iron and some bacterial products chelated with iron, followed by being up-taken by algae cell under photosynthesis.