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Journal of Bacteriology, February 2000, p. 789-795, Vol. 182, No. 3
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Identification of an Extradiol Dioxygenase Involved in Tetralin Biodegradation: Gene Sequence Analysis and Purification and Characterization of the Gene Product

Eloísa Andújar,1 María José Hernáez,1 Stefan R. Kaschabek,2 Walter Reineke,2 and Eduardo Santero1,*

Departamento de Genética, Facultad de Biología, Universidad de Sevilla, 41080 Seville, Spain,1 and Chemische Mikrobiologie, Bergische Universität-Gesamthochschule Wuppertal, D-42097 Wuppertal, Germany2

Received 8 September 1999/Accepted 9 November 1999

A genomic region involved in tetralin biodegradation was recently identified in Sphingomonas strain TFA. We have cloned and sequenced from this region a gene designated thnC, which codes for an extradiol dioxygenase required for tetralin utilization. Comparison to similar sequences allowed us to define a subfamily of 1,2-dihydroxynaphthalene extradiol dioxygenases, which comprises two clearly different groups, and to show that ThnC clusters within group 2 of this subfamily. 1,2-Dihydroxy-5,6,7,8-tetrahydronaphthalene was found to be the metabolite accumulated by a thnC insertion mutant. The ring cleavage product of this metabolite exhibited behavior typical of a hydroxymuconic semialdehyde toward pH-dependent changes and derivatization with ammonium to give a quinoline derivative. The gene product has been purified, and its biochemical properties have been studied. The enzyme is a decamer which requires Fe(II) for activity and shows high activity toward its substrate (Vmax, 40.5 U mg-1; Km, 18.6 µM). The enzyme shows even higher activity with 1,2-dihydroxynaphthalene and also significant activity toward 1,2-dihydroxybiphenyl or methylated catechols. The broad substrate specificity of ThnC is consistent with that exhibited by other extradiol dioxygenases of the same group within the subfamily of 1,2-dihydroxynaphthalene dioxygenases.

* Corresponding author. Mailing address: Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Ap. 1095, 41080 Sevilla, Spain. Phone: 34-95-4557106. Fax: 34-95-4557104. E-mail: esantero{at}cica.es.

Journal of Bacteriology, February 2000, p. 789-795, Vol. 182, No. 3
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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