Isolation And Characterization Of Highly Efficient Erythromycin-degrading Bacteria

Antibiotic drug is one of the drugs which have been widely used. The characteristics of wastewater which came from pharmaceutical process are high concentrations of COD and salt concentration, high color, large taste, and hard to be biodegradated. Currently, the environmental researchers are interested in the biological treatment of antibiotic wastewater. One of the most significant parts during the treatment process is how to domesticate and screen the bacteria with high efficient degradation. Such bacteria should be able to tolerate the antibiotics and other organic contaminants in the wastewater.This theme had screened and domesticated three high drug-resistant and high degradation strains named JA-1, JA-2 and JA-3 respectively, and then made systematic researches on their physiological and biochemical characteristics, growth conditions, degradation performance, drug resistance mechanism and so on.The characteristic analysis of morphological and physiochemical showed that JA-1 belonged to genus Klebsiella (Klebsiella. sp.); JA-2 belonged to genus Acidminococcus (Acidminococcus. sp.); and JA-3 belonged to genus Protens (Protens. Sp.). The optimum growth conditions of three strains were studied by spectrophotometric turbidimetry. The result showed that the carbon sources of JA-1, JA-2 and JA-3 were glucose; the nitrogen source of JA-1 was ammonium sulfate, while those of JA-2 and JA-3 were yeast extract; the optimum growth times of JA-1, JA-2 and JA-2 were 24 hours,49 hours, and 28 hours respectively; the optimum temperatures of JA-1, JA-2 and JA-3 were in the range of 26℃-40℃; the optimum initial pH of JA-1, JA-2 and JA-3 were in the range of 6-9. And all of the stains had a strong salt-tolerance and grew well in high NaCl concentration, of which the salt-tolerance concentration of JA-3 reaches 50 g/L. And the result of drug-resistant test showed that erythromycin has little effect on JA-2 and JA-3's growth, while it has great effect on JA-1's, when erythromycin concentrations are beyond 8g/L.In order to investigate the degradation abilities of three stains on erythromycin, sulfuric acid spectrophotometric method was adopted to detect erythromycin concentration in treated wastewater, while the fast-digestion spectrophotometric method was to detect COD concentration. The optimal degradation conditions were determined by changing the conditions of sources of carbon and nitrogen, pH, inoculation, temperature, incubation time and erythromycin concentration. The results showed the optimal degradation conditions as follow:(1) In the simulation wastewater the optimal degradation condition of JA-1 was anaerobic cultured for 56h in the condition of inoculation 8%, initial pH 7, temperature 35℃. And its maximum erythromycin and COD removal rate were 64.2% and 58.9% respectively.(2) In the simulation wastewater the optimal degradation condition of JA-2 was anaerobic cultured for 80h in the condition of inoculation 8%, initial pH 8, temperature 35℃. And its maximum erythromycin and COD removal rate were 72.0% and 66.2% respectively.(3) In the simulation wastewater the optimal degradation condition of JA-3 was anaerobic cultured for 56h in the condition of inoculation 8%, initial pH 8, temperature 35℃. And its maximum erythromycin and COD removal rate were 71.2% and 52.1% respectively.Meanwhile, the experimental result on complex microbial strains showed that the COD degradation rates of complex microbial strains were higher than those of single ones, while their erythromycin degradation rates were similar. It is because that different bacteria had synergistic effects on each other. Thus special degradation chains formed between them. Among the results, the optimal combinations of JA-1+JA-2 and JA-1+JA-3, whose COD degradation rates were 68.1% and 67.1% respectively.Finally, a study was performed on the effect of erythromycin concentration on the degration rate. It showed that the erythromycin concentration had greater effect on the degradation rate of COD than that of erythromycin. And then, the preliminary analysis on the drug-resistance mechanism suggested that the induction of erythromycin on microorganisms caused the variations in chromosomal gene and formed microbial drug-resistance or toxic tolerance. In all, it is very practical that it make biological method feasible to treat with erythromycin wastewater.