Abstract: Four strains capable of degrading polyvinyl alcohol （PVA） were separated from natural specimens‚and two mutants‚S7（Str r ‚Kan s ） and K15（Str s ‚Kan r ）‚which are of single drug resistance‚were obtained via UV－irradia-tion．The effects of various factors on the preparation and the regeneration rates of the protoplast were systematically ana-lyzed．By the protoplast fusion of S7and K15as parent strains and via orthorhombic tests‚the conditions of protoplast fu-sion were then optimized‚in which the fusion rate was up to4．603×10－5 ．It is found that the fusion strain F4can clean 87％ of PVA when it is cultured into activated sludge‚which is3～4times that of ordinary activated sludge．

Key words: protoplast fusion, strain breeding, PVA degradation