[Improvement of heavy metal removing strain by protoplast combination mutant]

Ultraviolet and HNO2 were selected as the mutagens to perform the single factor and multi-factor induction mutation towards Candida utilis CR-001. Six mutant strains which possessed high heavy metal removal efficiency and high resistance to Cr6+ were obtained through combined induction with UV and HNO2. After they were subcultured for 10 generations, the diameter of bacteriostatic circle of CRC2811-1 and CRC7-2 was reduced to 1.7 mm and 1.2 mm respectively, while the Cr6+ removal efficiency of CRC2811-1 was increased from 80.2% to 95.2%, and that of CRC7-2 was from 81.2% to 94.7%. The stability of the other 4 mutant strains was rather stable. Furthermore, precipitation of chromium outside or inside the cell was studied by using combined technique of scanning electron microscopy(SEM), transmission electron microscopy (TEM), and atomic force microscopy(AFM), and the mechanism of chromium removal improvement by the mutant strains was discussed.