Improvement of chromium biosorption by UV–HNO2 cooperative mutagenesis in Candida utilis

The present study focused on the improvement of chromium resistance and biosorption efficiency in Candida utilis CR-001 utilizing protoplast mutagenesis technology. Through ultraviolet (UV) radiation, HNO2 treatment and chromium acclimatization, six preferred mutants of C. utilis CR-001 were screened out, namely, CRU132-26, CRC7-2, CRC2811-1, CRC2811-2, CRC2814-8 and CRY182-1. The removal efficiency of these mutants for 20 mg/L Cr(VI) solutions were 85.6%, 95.2%, 87.0%, 82.5%, 94.7% and 82.7%, respectively, noticeably greater than that of the parent strain CR-001 (79.5%). Furthermore, CRC2811-1 exhibited outstanding application potential with high removal efficiency and low dosage over a wide range of pH. Cell surface and inner details of CRC2811-1 and its parent strain CR-001 were analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) in order to explore possible changes caused by inducement. The results showed that Cr-sorption of CR-001 mainly depended on intracellular accumulation, but for CRC2811-1, cell surface deposition was also involved in improving its chromium biosorption capacity.