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Applied and Environmental Microbiology, April 2000, p. 1429-1434, Vol. 66, No. 4
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

The Function of Cytoplasmic Flavin Reductases in the Reduction of Azo Dyes by Bacteria

Rainer Russ,dagger Jörg Rau, and Andreas Stolz*

Institut für Mikrobiologie, Universität Stuttgart, 70569 Stuttgart, Germany

Received 10 August 1999/Accepted 11 January 2000

A flavin reductase, which is naturally part of the ribonucleotide reductase complex of Escherichia coli, acted in cell extracts of recombinant E. coli strains under aerobic and anaerobic conditions as an "azo reductase." The transfer of the recombinant plasmid, which resulted in the constitutive expression of high levels of activity of the flavin reductase, increased the reduction rate for different industrially relevant sulfonated azo dyes in vitro almost 100-fold. The flavin reductase gene (fre) was transferred to Sphingomonas sp. strain BN6, a bacterial strain able to degrade naphthalenesulfonates under aerobic conditions. The flavin reductase was also synthesized in significant amounts in the Sphingomonas strain. The reduction rates for the sulfonated azo compound amaranth were compared for whole cells and cell extracts from both recombinant strains, E. coli, and wild-type Sphingomonas sp. strain BN6. The whole cells showed less than 2% of the specific activities found with cell extracts. These results suggested that the cytoplasmic anaerobic "azo reductases," which have been described repeatedly in in vitro systems, are presumably flavin reductases and that in vivo they have insignificant importance in the reduction of sulfonated azo compounds.

* Corresponding author. Mailing address: Institut für Mikrobiologie, Universität Stuttgart, 70569 Stuttgart, Germany. Phone: 49-711-6855489. Fax: 49-711-6855725. E-mail: Andreas.Stolz{at}PO.Uni-Stuttgart.DE.

dagger Present address: Lehrbereich Biotechnologie, Universität Kaiserslautern, 67663 Kaiserslautern, Germany.

Applied and Environmental Microbiology, April 2000, p. 1429-1434, Vol. 66, No. 4
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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