Affiliation:
1. Biology Department, Carleton University, Ottawa, Ontario, Canada K1S 5B6
Abstract
ABSTRACT
Nitroheterocyclic and nitroaromatic compounds constitute an enormous range of chemicals whose potent biological activity has significant human health and environmental implications. The biological activity of nitro-substituted compounds is derived from reductive metabolism of the nitro moiety, a process catalyzed by a variety of nitroreductase activities. Resistance of bacteria to nitro-substituted compounds is believed to result primarily from mutations in genes encoding oxygen-insensitive nitroreductases. We have characterized the
nfsA
and
nfsB
genes of a large number of nitrofuran-resistant mutants of
Escherichia coli
and have correlated mutation with cell extract nitroreductase activity. Our studies demonstrate that first-step resistance to furazolidone or nitrofurazone results from an
nfsA
mutation, while the increased resistance associated with second-step mutants is a consequence of an
nfsB
mutation. Inferences made from mutation about the structure-function relationships of NfsA and NfsB are discussed, especially with regard to the identification of flavin mononucleotide binding sites. We show that expression of plasmid-carried
nfsA
and
nfsB
genes in resistant mutants restores sensitivity to nitrofurans. Among the 20 first-step and 53 second-step mutants isolated in this study, 65 and 49%, respectively, contained insertion sequence elements in
nfsA
and
nfsB
. IS
1
integrated in both genes, while IS
30
and IS
186
were found only in
nfsA
and IS
2
and IS
5
were observed only in
nfsB
. Insertion hot spots for IS
30
and IS
186
are indicated in
nfsA
, and a hot spot for IS
5
insertion is evident in
nfsB
. We discuss potential regional and sequence-specific determinants for insertion sequence element integration in
nfsA
and
nfsB
.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
176 articles.
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