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Applied and Environmental Microbiology, October 2000, p. 4247-4252, Vol. 66, No. 10
Department of Biochemistry, Molecular
Biology, and Biophysics,1 Biological
Process Technology Institute,3 Center
for Microbial and Plant Genomics,2 and
Department of Soil, Water, and Climate,4
University of Minnesota, St. Paul, Minnesota 55108
Received 20 April 2000/Accepted 17 July 2000
Bacterial atrazine catabolism is initiated by the enzyme atrazine
chlorohydrolase (AtzA) in Pseudomonas sp. strain ADP. Other triazine herbicides are metabolized by bacteria, but the enzymological basis of this is unclear. Here we begin to address this by
investigating the catalytic activity of AtzA by using substrate
analogs. Purified AtzA from Pseudomonas sp. strain ADP
catalyzed the hydrolysis of an atrazine analog that was substituted at
the chlorine substituent by fluorine. AtzA did not catalyze the
hydrolysis of atrazine analogs containing the pseudohalide azido,
methoxy, and cyano groups or thiomethyl and amino groups. Atrazine
analogs with a chlorine substituent at carbon 2 and N-alkyl
groups, ranging in size from methyl to t-butyl, all
underwent dechlorination by AtzA. AtzA catalyzed hydrolytic
dechlorination when one nitrogen substituent was alkylated and the
other was a free amino group. However, when both amino groups were
unalkylated, no reaction occurred. Cell extracts were prepared from
five strains capable of atrazine dechlorination and known to contain
atzA or closely homologous gene sequences: Pseudomonas sp. strain ADP, Rhizobium strain
PATR, Alcaligenes strain SG1, Agrobacterium
radiobacter J14a, and Ralstonia picketti D. All
showed identical substrate specificity to purified AtzA from
Pseudomonas sp. strain ADP. Cell extracts from
Clavibacter michiganensis ATZ1, which also contains a gene
homologous to atzA, were able to transform atrazine analogs
containing pseudohalide and thiomethyl groups, in addition to the
substrates used by AtzA from Pseudomonas sp. strain ADP.
This suggests that either (i) another enzyme(s) is present which
confers the broader substrate range or (ii) the AtzA itself has a
broader substrate range.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Substrate Specificity of Atrazine Chlorohydrolase
and Atrazine-Catabolizing Bacteria
*
Corresponding author. Mailing address: Department of
Biochemistry, Molecular Biology, and Biophysics, Biological Process
Technology Institute, 1479 Gortner Ave., University of Minnesota, St.
Paul, MN 55108. Phone: (612) 625-3785. Fax: (612) 625-1700. E-mail: wackett{at}biosci.cbs.umn.edu.
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