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

Predation of Poterioochromonas sp. on prey Microcystis is normally a one way process, i.e., prey cells were continuously ingested and gradually disappeared. However, it was not always the same. Occasionally, a patch of blue-green 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 Poterioochromonas 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 If 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