金藻吞噬微囊藻产生的无毒变异株与产毒原始株的比较

COMPARISON BETWEEN THE TOXIC MICROCYTIS SPECIES AND NON-TOXIC MICROCYSTIS SPECIES ORIGINATED FROM THE COCULTURE OF MICROCYSTIS AND POTERIOOCHROMOAS SP.

分别从喂食三株原始产毒铜绿微囊藻Microcystis aeruginosa(AC、DS和PCC 7820)的金藻Poterioochromonassp.培养物中获得三株藻,以Nest PCR方法(引物对CC/CG和CH/CI)确定此三株藻均为微囊藻属藻株。HPLC测试结果显示这三株藻均不产生微囊藻毒素。显示Poterioochromonassp.具有将产毒微囊藻转化为无毒微囊藻的能力。比较产毒原始株与无毒变异株的生理特性发现,变异株的类胡萝卜素/叶绿素比值高于原始株;而光反应曲线结果表明,变异株的PSⅡ的量子产率和光合作用活力高于原始产毒株,并且变异株在较低光强下就可达到最大的光合作用活力。显示喂食后产生的变异株比原始株有较高的光合作用效率。变异株的藻蓝蛋白/叶绿素比值则低于原始株,光合作用最适光强低于变异株,并且显示产毒原始株通过增加藻蓝蛋白的相对含量来提高对光照的吸收。变异株具有较高的光合作用效率和藻蓝蛋白含量可能是其能够在微囊藻和金藻混合培养的群体中占优势的原因之一。

Predation of Poterioochromonas sp. on prey Microcystis is normally a one way process, i. e. , prey ceils were continuously ingested and gradually disappeared. However, it was not always the same. Occasionally, a patch of bluegreen colored cells may re-appear from the bottom of the culture flask and gradually proliferated. Based on this phenomenon, experiments were designed by using three strains of Microcystis- M. aeruginosa AC, DS and PCC 7820-as prey organisms co-cultured with predator Poterioochromonas sp. , respectively. After one or two months, eventually ＂transformed＂ Microcystis populations were obtained separately from each of co-cultured treatment. Nest PCR and 16S rDNA analysis identified these transformed cells to be Microcystis sp.. Furthermore, it was astonishingly found that these three transformed Microcystis populations had lost the microcystin-producing ability. The result strongly suggested that Poterioo-chromonas sp. played an important role in transforming the toxicity of Microcystis during predating process. Transformed, non-toxic Microcystis had higher value of caroteinoids/chlorophyll ratio but lower value of cyanophycin/ chlorophyll ratio compared with original toxic strains. Light response curves indicated that the PS 11 quantum yield and photosynthetic activity of these non-toxic strains were higher than that of original toxic strains, moreover, non-toxic strains achieved the maximum photosynthetic activity at lower light intensity than that of toxic strains. This might explain why the non-toxic transformed strains outgrew the toxic wild strains in Microcystis and Poteroochromonas co-culture.