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Applied and Environmental Microbiology, February 2006, p. 1476-1486, Vol. 72, No. 2
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.2.1476-1486.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Degradation of 4-Chloro-2-Methylphenoxyacetic Acid in Top- and Subsoil Is Quantitatively Linked to the Class III tfdA Gene

Jacob Bælum,1,2 Trine Henriksen,1 Hans Christian Bruun Hansen,2 and Carsten Suhr Jacobsen1,2,3*

Geological Survey of Denmark and Greenland (GEUS), Department of Geochemistry,1 Royal Veterinary and Agricultural University (KVL), Department of Natural Sciences,2 Royal Veterinary and Agricultural University (KVL), Department of Ecology, Copenhagen, Denmark3

Received 22 August 2005/ Accepted 22 November 2005

The tfdA gene is known to be involved in the first step of the degradation of the phenoxy acid herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) in several soil bacteria, but bacteria containing other tfdA-like genes have been isolated as well. A quantitative real-time PCR method was used to monitor the increase in the concentration of tfdA genes during degradation of MCPA in sandy topsoil and subsoil over a period of 115 days. Quantitative PCR revealed growth in the tfdA-containing bacterial community, from 500 genes g–1 soil to approximately 3 x 104 genes g–1 soil and to 7 x 105 genes g–1 soil for topsoil initially added to 2.3 mg MCPA kg–1 (dry weight) soil and 20 mg MCPA kg–1 (dry weight) soil, respectively. We analyzed the diversity of the tfdA gene during the degradation experiment. Analyses of melting curves of real-time PCR amplification products showed that a shift in the dominant tfdA population structure occurred during the degradation period. Further denaturing gradient gel electrophoresis and sequence analysis revealed that the tfdA genes responsible for the degradation of MCPA belonged to the class III tfdA genes, while the tfdA genes present in the soil before the occurrence of degradation belonged to the class I tfdA genes. The implications of these results is that the initial assessment of functional genes in soils does not necessarily reflect the organisms or genes that would carry out the degradation of the compounds in question.

* Corresponding author. Mailing address: Department of Geochemistry, Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. Phone: 45 3814 2313. Fax: 45 3814 2050. E-mail: csj{at}geus.dk.

Applied and Environmental Microbiology, February 2006, p. 1476-1486, Vol. 72, No. 2
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.2.1476-1486.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Baelum, J., Jacobsen, C. S. (2009). TaqMan Probe-Based Real-Time PCR Assay for Detection and Discrimination of Class I, II, and III tfdA Genes in Soils Treated with Phenoxy Acid Herbicides. Appl. Environ. Microbiol. 75: 2969-2972 [Abstract] [Full Text]  
  • Fredslund, L., Vinther, F. P., Brinch, U. C., Elsgaard, L., Rosenberg, P., Jacobsen, C. S. (2008). Spatial Variation in 2-Methyl-4-chlorophenoxyacetic Acid Mineralization and Sorption in a Sandy Soil at Field Level. J. Environ. Qual. 37: 1918-1928 [Abstract] [Full Text]  
  • Amos, B. K., Sung, Y., Fletcher, K. E., Gentry, T. J., Wu, W.-M., Criddle, C. S., Zhou, J., Loffler, F. E. (2007). Detection and Quantification of Geobacter lovleyi Strain SZ: Implications for Bioremediation at Tetrachloroethene- and Uranium-Impacted Sites. Appl. Environ. Microbiol. 73: 6898-6904 [Abstract] [Full Text]  


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