Isolation,identification, and decolorization capabilities of strain ZW-4 for Pigment Red 23

A strain ZW-4 with remarkable ability to decolorize the Pigment Red 23 was isolated from aerobic sludge by the method of concentration gradient domestication. The strain was identified as Prototheca sp. according to its morphological characters and 16S rDNA sequence analysis. Experiments on the effect of decolorization conditions were carried out under aerobic conditions. The results showed that the best nutrient source was yeast powder, and the optimum conditions were 1% yeast powder, 5% inoculum, pH 7.5, temperature 35 °C, and salinity less than 4%. Under these conditions, the decolorization rate of Pigment Red 23 (initial concentration of 100 mg L^?1) was more than 91% when the strain ZW-4 was cultivated for 18 h. The strain also showed better salt tolerance property, which ranged from 6 to 8%. Besides, spectrophotometric analysis demonstrated that the decolorization mechanism of Pigment Red 23 was mainly biological degradation. Furthermore, toxicity tests indicated that the toxicity of Pigment Red 23 after decolorization had reduced noticeably with the strain ZW-4.