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Applied and Environmental Microbiology, December 2005, p. 7643-7649, Vol. 71, No. 12
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.12.7643-7649.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Regulation and Characterization of Two Nitroreductase Genes, nprA and nprB, of Rhodobacter capsulatus
Eva Pérez-Reinado,1 Rafael Blasco,2 Francisco Castillo,1 Conrado Moreno-Vivián,1 and M. Dolores Roldán1*Departamento de Bioquímica y Biología Molecular, Campus de Rabanales, Edificio Severo Ochoa, 1st Planta, Universidad de Córdoba, 14071 Córdoba, Spain,1 Departamento de Bioquímica, Biología Molecular y Genética, Facultad de Veterinaria, Universidad de Extremadura, 11071 Cáceres, Spain2
Received 25 May 2005/ Accepted 22 July 2005
Among photosynthetic bacteria, strains B10 and E1F1 of Rhodobacter capsulatus photoreduce 2,4-dinitrophenol (DNP), which is stoichiometrically converted into 2-amino-4-nitrophenol by a nitroreductase activity. The reduction of DNP is inhibited in vivo by ammonium, which probably acts at the level of the DNP transport system and/or physiological electron transport to the nitroreductase, since this enzyme is not inhibited by ammonium in vitro. Using the complete genome sequence data for strain SB1003 of R. capsulatus, two putative genes coding for possible nitroreductases were isolated from R. capsulatus B10 and disrupted. The phenotypes of these mutant strains revealed that both genes are involved in the reduction of DNP and code for two major nitroreductases, NprA and NprB. Both enzymes use NAD(P)H as the main physiological electron donor. The nitroreductase NprA is under ammonium control, whereas the nitroreductase NprB is not. In addition, the expression of the nprB gene seems to be constitutive, whereas nprA gene expression is inducible by a wide range of nitroaromatic and heterocyclic compounds, including several dinitroaromatics, nitrofuran derivatives, CB1954, 2-aminofluorene, benzo[a]pyrene, salicylic acid, and paraquat. The identification of two putative mar/sox boxes in the possible promoter region of the nprA gene and the induction of nprA gene expression by salicylic acid and 2,4-dinitrophenol suggest a role in the control of the nprA gene for the two-component MarRA regulatory system, which in Escherichia coli controls the response to some antibiotics and environmental contaminants. In addition, upregulation of the nprA gene by paraquat indicates that this gene is probably a member of the SoxRS regulon, which is involved in the response to stress conditions in other bacteria.
* Corresponding author. Mailing address: Departamento de Bioquímica y Biología Molecular, Campus de Rabanales, Edificio Severo Ochoa, 1st Planta, Universidad de Córdoba, 14071 Córdoba, Spain. Phone: 34 957218318. Fax: 34 957218588. E-mail: bb2rorum{at}uco.es.
Applied and Environmental Microbiology, December 2005, p. 7643-7649, Vol. 71, No. 12
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.12.7643-7649.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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