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Microbiology 155 (2009), 3641-3651; DOI  10.1099/mic.0.032086-0
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Microbiology 155 (2009), 3641-3651; DOI  10.1099/mic.0.032086-0
© 2009 Society for General Microbiology

Genuine genetic redundancy in maleylacetate-reductase-encoding genes involved in degradation of haloaromatic compounds by Cupriavidus necator JMP134

Danilo Pérez-Pantoja1, Raúl A. Donoso2, Miguel A. Sánchez1 and Bernardo González1,2

1 Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, P. Universidad Católica de Chile, Millennium Nucleus on Microbial Ecology and Environmental Microbiology and Biotechnology, NM-EMBA, Center for Advanced Studies in Ecology and Biodiversity, CASEB, Santiago, Chile
2 Facultad de Ingeniería y Ciencia, Universidad Adolfo Ibáñez, Santiago, Chile

Maleylacetate reductases (MAR) are required for biodegradation of several substituted aromatic compounds. To date, the functionality of two MAR-encoding genes (tfdFI and tfdFII) has been reported in Cupriavidus necator JMP134(pJP4), a known degrader of aromatic compounds. These two genes are located in tfd gene clusters involved in the turnover of 2,4-dichlorophenoxyacetate (2,4-D) and 3-chlorobenzoate (3-CB). The C. necator JMP134 genome comprises at least three other genes that putatively encode MAR (tcpD, hqoD and hxqD), but confirmation of their functionality and their role in the catabolism of haloaromatic compounds has not been assessed. RT-PCR expression analyses of C. necator JMP134 cells exposed to 2,4-D, 3-CB, 2,4,6-trichlorophenol (2,4,6-TCP) or 4-fluorobenzoate (4-FB) showed that tfdFI and tfdFII are induced by haloaromatics channelled to halocatechols as intermediates. In contrast, 2,4,6-TCP only induces tcpD, and any haloaromatic compounds tested did not induce hxqD and hqoD. However, the tcpD, hxqD and hqoD gene products showed MAR activity in cell extracts and provided the MAR function for 2,4-D catabolism when heterologously expressed in MAR-lacking strains. Growth tests for mutants of the five MAR-encoding genes in strain JMP134 showed that none of these genes is essential for degradation of the tested compounds. However, the role of tfdFI/tfdFII and tcpD genes in the expression of MAR activity during catabolism of 2,4-D and 2,4,6-TCP, respectively, was confirmed by enzyme activity tests in mutants. These results reveal a striking example of genetic redundancy in the degradation of aromatic compounds.

Correspondence
Bernardo González
bernardo.gonzalez{at}uai.cl

Abbreviations: 2-CMA, 2-chloromaleylacetate; 2,4-D, 2,4-dichlorophenoxyacetate; 2,4,6-TCP, 2,4,6-trichlorophenol; 3-CB, 3-chlorobenzoate; 4-FB, 4-fluorobenzoate; MA, maleylacetate; MAR, maleylacetate reductase(s)






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