No abstract

Bacteria are present extensively in the environment. Investigation of their antioxidant properties will be useful for further study on atrazine stress tolerance of bacteria and the defense mechanism of antioxidant enzymes against atrazine or other triazine herbicides. Superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST) and total antioxidant capacity (T-AOC) from one Gram-negative representative strain Escherichia coli K12 and one Gram-positive representative strain Bacillus subtilis B19, respectively, were tested for response to atrazine stress. The results indicated that SOD, CAT, GST and T-AOC were induced upon exposure to atrazine. The growth of two bacteria was better in the absence than in the presence of atrazine, indicating that atrazine can decrease bacterial growth. The changes of enzyme activities indicate the presence of oxidative stress. Oxidative stress induced by atrazine may be due to imbalance of redox potential in bacterial cells, which leads to bacterial metabolic disorder.

Statistical experimental designs provided by statistical analysis system (SAS) software were applied to optimize the fermentation medium composition for the production of atrazine-degrading Acinetobacter sp. DNS32 in shake-flask cultures. A “Plackett-Burman Design” was employed to evaluate the effects of different components in the medium. The concentrations of corn flour, soybean flour, and K2HPO4 were found to significantly influence Acinetobacter sp. DNS32 production. The steepest ascent method was employed to determine the optimal regions of these three significant factors. Then, these three factors were optimized using central composite design of “response surface methodology.” The optimized fermentation medium composition was composed as follows (g/L): corn flour 39.49, soybean flour 25.64, CaCO3 3, K2HPO4 3.27, MgSO4·7H2O 0.2, and NaCl 0.2. The predicted and verifiable values in the medium with optimized concentration of components in shake flasks experiments were 7.079 × 108 CFU/mL and 7.194 × 108 CFU/mL, respectively. The validated model can precisely predict the growth of atrazine-degraing bacterium, Acinetobacter sp. DNS32.

It could be shown that atrazine bound to microbes DNA in black soil by using ethidium bromide (EB) as a fluorescence probe. To study the interaction between atrazine and the microbes DNA in black soil, spectral absorption and fluorescence analysis were adopted. Atrazine, when bound to DNA, showed a hyperchromic and red shift in the absorption spectra and fluorescence quenching (>50%) in the fluorescence spectra, which indicated the intercalation. The effect of phosphate ion showed that there were electrostatic attractions with the anionic sugar‐phosphate backbone of DNA. The ratio plots “fluorescence intensities in the absence” to “fluorescence intensities in the presence of a quencher” (Fo/F) showed that the quenching of fluorescence by atrazine was a combined quenching process. The results indicated that there were two binding modes, intercalation and electrostatic attractions, happened simultaneously. The hyperchromicity in the absorption spectra indicated the breaking or denaturation of DNA, and a fluorescence inhibiting effect showed that atrazine had a high ability to bind to the DNA of black soil microbes. Based on these results, it was speculated that the binding between atrazine and the DNA the black soil microbes could inhibit some functions of the nucleic acid, restrain microbial activity or cause genotoxicity.

No abstract