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Applied and Environmental Microbiology, October 2007, p. 6421-6428, Vol. 73, No. 20
0099-2240/07/$08.00+0     doi:10.1128/AEM.01051-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Degradation of Carbazole by Microbial Cells Immobilized in Magnetic Gellan Gum Gel Beads{triangledown}

Xia Wang,1 Zhonghui Gai,2 Bo Yu,3 Jinhui Feng,1 Changyong Xu,1 Yong Yuan,1 Zhixin Lin,2 and Ping Xu1,2,3*

State Key Laboratory of Microbial Technology, Shandong University, Jinan 250100, People's Republic of China,1 Key Laboratory of Microbial Metabolism, Ministry of Education, College of Life Science and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China,2 Institute of Microbiology, Chinese Academy of Sciences, Beijing 100080, People's Republic of China3

Received 11 May 2007/ Accepted 13 August 2007

Polycyclic aromatic heterocycles, such as carbazole, are environmental contaminants suspected of posing human health risks. In this study, we investigated the degradation of carbazole by immobilized Sphingomonas sp. strain XLDN2-5 cells. Four kinds of polymers were evaluated as immobilization supports for Sphingomonas sp. strain XLDN2-5. After comparison with agar, alginate, and {kappa}-carrageenan, gellan gum was selected as the optimal immobilization support. Furthermore, Fe3O4 nanoparticles were prepared by a coprecipitation method, and the average particle size was about 20 nm with 49.65-electromagnetic-unit (emu) g–1 saturation magnetization. When the mixture of gellan gel and the Fe3O4 nanoparticles served as an immobilization support, the magnetically immobilized cells were prepared by an ionotropic method. The biodegradation experiments were carried out by employing free cells, nonmagnetically immobilized cells, and magnetically immobilized cells in aqueous phase. The results showed that the magnetically immobilized cells presented higher carbazole biodegradation activity than nonmagnetically immobilized cells and free cells. The highest biodegradation activity was obtained when the concentration of Fe3O4 nanoparticles was 9 mg ml–1 and the saturation magnetization of magnetically immobilized cells was 11.08 emu g–1. Additionally, the recycling experiments demonstrated that the degradation activity of magnetically immobilized cells increased gradually during the eight recycles. These results support developing efficient biocatalysts using magnetically immobilized cells and provide a promising technique for improving biocatalysts used in the biodegradation of not only carbazole, but also other hazardous organic compounds.

* Corresponding author. Mailing address: State Key Laboratory of Microbial Technology, Shandong University, Jinan 250100, People's Republic of China. Phone: 86-531-88564003. Fax: 86-531-88567250. E-mail: pingxu{at}sdu.edu.cn

{triangledown} Published ahead of print on 7 September 2007.

Applied and Environmental Microbiology, October 2007, p. 6421-6428, Vol. 73, No. 20
0099-2240/07/$08.00+0     doi:10.1128/AEM.01051-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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