| Biological sciences & biotechnology |
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| Isolation and characterization of diphenyl ether degrading bacterium Sphingomonas sp. DZ-3 |
| Feng Zhuo, Wang Sheng, Bai Naling, Zhao Yuhua* |
| (Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou 310058, China) |
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Abstract Polybrominated diphenyl ethers (PBDEs) are man-made flame-retardant chemicals that are widely used to decrease the flammability of plastics, electronic appliances textiles and polyurethanes. Annually, more than 67 400 tons of PBDEs including penta-, octa-, and deca-BDE were produced. PBDEs can be incorporated into polymers without any covalent bonds to adjacent materials. Because of the widespread production and improper disposal of these polymers, PBDEs have been accumulated in the environment. The toxicity of PBDEs is variable for different congeners. Some of them show neurotoxic toxicity in mice and dioxin-like endocrine disruption. In spite of the accumulation of PBDEs in the environment, few remediation technologies have been investigated sufficiently. A few works of biological degradation of PBDEs have been done in recent years.
An efficient diphenyl ether degrading bacterium strain DZ-3, which was able to utilize diphenyl ether as a sole source of carbon and energy under aerobic condition, was isolated from activated sludge of a wastewater treatment plant. The growth and degradation character of the strain were studied in order to offer some useful informations for the remediation of contamination.
In addition to the diphenyl ether degrading bacterium DZ-3, the other bacterium strain CZ-3 was also isolated, which can’t degrade biphenyl ether. But the mixed cultures of the two strains could enhance the degradation of diphenyl ether compared with DZ-3 cultivation. Based on 16S rDNA gene sequencing, the strains DZ-3 and CZ-3 were identified as Sphingomonas sp. DZ-3 and Ochrobactrum sp. CZ-3. Mixture design was used to adjust the proportion of each strain and the optimal ratio of inoculation size was DZ-3∶CZ-3=2∶3 . Diphenyl ether degradation experiments using high performance liquid chromatograph (HPLC) showed that the strain DZ-3 could degrade 71% of diphenyl ether (initial concentration of 835 mg/L) within 6 days, while the mixture of DZ-3 and CZ-3 could degrade 90% within 4 days. To further investigate the degree of metal ions affecting the biodegradation of Sphingomonas sp. DZ-3, a background propagation artificial neural network (ANN) was used to conduct a sensitive analysis on the individual variables. The ANN model showed satisfactory fits for the experimental data. The results indicated that Mg2+ appeared to be the most important metal ion for the biodegradation of DZ-3 with a relative importance of 31.01% followed by Co2+ (25.45%), Ni2+(15.12%) in which Mg2+ had a positive effect on the degradation, while Co2+ and Ni2+ had negative ones. In addition, the strain DZ-3 even catabolized biphenyl and monobrominated diphenyl ether. Meanwhile, the degradation of biphenyl ether in the polluted soil added with the exterior microorganism was studied by lab simulation. In lab simulation, the degradation percentage of diphenyl ether by Ochrobactrum sp CZ-3 and Sphingomonas sp. DZ-3 was 71% within 3 days and 98% within 6 days. The degradation effect was significant indicating that the mixed culture had great potential for remediation of contaminated soil.
In conclusion, the research on the characteristics of the diphenyl ether biodegradation can provide theoritical basis and experience about engineering application for bioremediation of diphenyl ether and PBDEs polluted sites.
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Published: 20 January 2015
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二苯醚降解菌鞘氨醇单胞菌DZ-3的分离及其降解特性
通过选择性富集从浙江上虞污水处理厂的活性污泥中分离获得2株细菌DZ-3和CZ-3。DZ-3能够以二苯醚为唯一碳源进行生长,CZ-3不能对二苯醚进行降解,但CZ-3和DZ-3的混合培养物能极大地提高对二苯醚的降解效率。对这2株菌进行16S rDNA鉴定,分别隶属于鞘氨醇单胞菌属（Sphingomonas sp.）以及苍白杆菌属（Ochrobactrum sp.）。无机盐降解实验表明,DZ-3在6 d内对初始质量浓度为835 mg/L的二苯醚的降解率为71%,而混合细菌以2∶3比例接种在4 d内的降解率为90%。通过人工神经网络的方法分析无机盐中金属离子对二苯醚降解效率的影响表明,Mg2+对降解的影响最大。在土壤中的降解实验表明,混合细菌在6 d内对土壤中二苯醚的降解率能够达到98%。
关键词：
二苯醚,
降解细菌,
降解率,
土壤修复
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