Molecular Mechanisms of Nitroarene Degradation
Final rept. 1 Jul 1999-30 Jun 2002
IOWA UNIV IOWA CITY DEPT OF MICROBIOLOGY
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The initial reaction in the degradation of 2-nitrotoluene by Pseudomonas sp. strain JS42 is catalyzed by 2-nitrotoluene dioxygenase 2NTDO. Electrons from NADH are transferred to 2NTDO via a reductase and a Rieske 2Fe-2S ferredoxin. The reductase was purified to homogeneity and shown to be an iron-sulfur flavoprotein. 2NTDO was purified and crystallized. The crystals diffracted to 3.8 on a synchrotron beamline. Preliminary analysis indicated that 2NTDO has similar structural features to naphthalene dioxygenase NDO from Pseudomonas sp. strain 9816. Better resolution is required for detailed structural studies. The genes encoding the nitrobenzene dioxygenase NBDO system in Comamonas sp. strain JS765 were cloned and sequenced. Four open reading frames nbzAaAbAcAd were identified as genes encoding the reductase, ferredoxin and alpha and beta subunits of the NBDO system. NBDO was purified from IPTG-induced cells of E. coli DH5apDTG927 expressing nbzAcAd. The enzyme is a Rieske non-heme iron dioxygenase closely related to 2NTDO and NDO. The genes encoding NBDO in JS765 and 2NTDO in JS42 are cotranscribed as operons under the control of identical transcriptional regulatory proteins NbzR and NtdR. The transcriptional start site for both operons are identical and several nitroaromatic compounds as well as salicylate and anthranilate can induce enzyme activity.