A study on ASP toxin production mechanism in diatom

研究了伪尼茨氏菌多系列培养中软骨藻酸（DA）的产生。培养1周或3周后制备的非无性系无细胞培养基在相同条件下继续培养5周。在整个培养过程中没有观察到DA的产生，这表明即使在高DA水平的P多系培养中，细菌本身也不产生DA。在透析膜分离的非无菌P多系培养（m. w . 5万切断）中，研究了无菌培养的DA产量。3周前，无菌培养细胞无或微量DA。3周后，无菌细胞的DA含量显著升高。DA含量与非无菌细胞相当，表明无菌细胞的DA产生与一些小于m. w.的化合物有关。研究了耐氏耐氏菌培养的DA产量和铁吸收情况。在固定生长阶段，硅藻细胞的DA含量随着细胞铁含量的增加而增加，表明DA的产生可能与不溶性铁的吸收有关，如P. multiseries。从菲律宾分离得到的X navis-varingica不仅能产生DA，还能产生异domoic酸A （IA）和B （TB）。只有3个有限地区的分离株产生IA和IB，而不是DA。在菲律宾以外的地区对navis-varingica的ASP毒素组成进行了调查，结果证实许多navis-varingica产生DA和TB，只有上述有限的分离株产生IA和TB。非无菌亚菌株的毒素组成基本稳定，但有一株无菌亚菌株将其原有的毒素组成DA-IB变为IA-TB，说明某些细菌或细菌组合可能影响了褐藻毒素组成。

Domoic acid (DA) production by bacteria itself was investigated in Pseudo-nitzschia multiseries culture. Non-axenic cell-free medium prepared from 1-or 3-week culture was further cultured for 5 weeks under the same conditions. No DA production was observed during the entire culture period, suggesting that bacteria itself does not produce DA even in P multiseries culture that shows high level of DA. DA production of axenic culture was investigated when cultured in non-axenic P multiseries culture separating with dialysis membrane (m. w 50,000 cut off). Before 3-week, axenic culture cells showed no or trace amount of DA. After 3-week, DA content of axenic cells increased significantly. DA contents were comparable to that of non-axenic cells, suggesting that DA production of axenic cells occurred in association with some compounds smaller than m. w. 50,000 came from non-axenic culture. Nitzschia navis-varingica culture was examined for DA production and iron uptake. DA content of the diatom cells increased as the iron content of the cells increased during the stationary growth phase, suggesting that DA might be produced in association with the uptake of insoluble iron as in case of P. multiseries. X navis-varingica isolated from the Philippines was confirmed to produce not only DA but also isodomoic acids A (IA) and B (TB). Isolates from only 3 limited areas produced IA and IB instead of DA. Many other isolates from other places produced DA and IB. ASP toxin composition of N. navis-varingica was investigated outside the Philippines, resulting in confirmation that many N. navis-varingica produces DA and TB and only limited isolates described above produces IA and TB. Toxin composition in non-axenic sub-strain was stable, but one axenic sub-strain changed its original toxin composition DA-IB to IA-TB, suggesting that some bacteria or combination of bacteria might effect the toxin composition of N navis-varingica.