Isolation and Identification of a Chromium-Tolerant Fungus and its Chromium-Tolerant Mechanism Based on Antioxidant Enzymes Response

A strain of fungus was isolated from 100 mg/L 1∶1 Cr-EDTA solution contaminated by fungi in the laboratory. Results of identification by morphology and molecular biology show that the strain belongs to the genus downy mildew. Its optimal growth conditions are culture temperature of 30 ℃ and pH of 6 or 7. Chromium stress test confirmed that the strain could tolerate the hexavalent chromium with the maximum concentration of 1000 mg/L. By measuring the activities of total antioxidant enzymes (T-AOC), total superoxide dismutase (T-SOD) and catalase (CAT) of the strain under different concentrations of chromium, we investigated the response path of antioxidant enzyme system of the strain and the correlation of different antioxidant enzyme activity response under chromium stress, in order to clarify the chromium resistance mechanism of the strain from the perspective of antioxidant enzyme system. Results show that, under Cr stress, all the activities of T-SOD, T-AOC and CAT showed an increasing trend, among which the activity of T-SOD increased the fastest. When the Cr concentration was 155 mg/L, the activity of T-SOD was 4 times of that of the blank control group, and the activity of CAT was 3.8 times of that of the control group, while the activity of T-AOC was 2 times of that of the control group. These results indicate that the response sequence of antioxidant enzyme activities in the strain to Cr⁶⁺ stress is T-SOD>CAT>T-AOC, and there is a positive linear correlation between T-AOC and T-SOD activities, T-AOC and over-CAT activities, and T-SOD and CAT activities, respectively.