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Applied and Environmental Microbiology, July 2000, p. 2965-2971, Vol. 66, No. 7
Air Force Research Laboratory/MLQR, Tyndall
Air Force Base, Florida 32403-5323
Received 22 March 2000/Accepted 18 April 2000
Pseudomonas pseudoalcaligenes JS45 grows on
nitrobenzene by a partially reductive pathway in which the intermediate
hydroxylaminobenzene is enzymatically rearranged to 2-aminophenol by
hydroxylaminobenzene mutase (HAB mutase). The properties of the enzyme,
the reaction mechanism, and the evolutionary origin of the gene(s)
encoding the enzyme are unknown. In this study, two open reading frames (habA and habB), each encoding an HAB mutase
enzyme, were cloned from a P. pseudoalcaligenes JS45
genomic library and sequenced. The open reading frames encoding HabA
and HabB are separated by 2.5 kb and are divergently transcribed. The
deduced amino acid sequences of HabA and HabB are 44% identical. The
HAB mutase specific activities in crude extracts of Escherichia
coli clones synthesizing either HabA or HabB were similar to the
specific activities of extracts of strain JS45 grown on nitrobenzene.
HAB mutase activity in E. coli extracts containing HabB
withstood heating at 85°C for 10 min, but extracts containing HabA
were inactivated when they were heated at temperatures above 60°C.
HAB mutase activity in extracts of P. pseudoalcaligenes
JS45 grown on nitrobenzene exhibited intermediate temperature
stability. Although both the habA gene and the
habB gene conferred HAB mutase activity when they were
separately cloned and expressed in E. coli, reverse transcriptase PCR analysis indicated that only habA is
transcribed in P. pseudoalcaligenes JS45. A mutant strain
derived from strain JS45 in which the habA gene was
disrupted was unable to grow on nitrobenzene, which provided
physiological evidence that HabA is involved in the degradation of
nitrobenzene. A strain in which habB was disrupted grew on
nitrobenzene. Gene Rv3078 of Mycobacterium tuberculosis
H37Rv encodes a protein whose deduced amino acid sequence is 52%
identical to the HabB amino acid sequence. E. coli
containing M. tuberculosis gene Rv3078 cloned into
pUC18 exhibited low levels of HAB mutase activity. Sequences that
exhibit similarity to transposable element sequences are present
between habA and habB, as well as downstream of
habB, which suggests that horizontal gene transfer resulted
in acquisition of one or both of the hab genes.
0099-2240/00/$04.00+0
Sequence Analysis and Initial Characterization of
Two Isozymes of Hydroxylaminobenzene Mutase from
Pseudomonas pseudoalcaligenes JS45


*
Corresponding author. Mailing address: Air Force
Research Laboratory/MLQR, 139 Barnes Dr., Tyndall Air Force Base, FL
32403-5323. Phone: (850) 283-6058. Fax: (850) 283-6090. E-mail:
jspain{at}mlq.afrl.af.mil.
Present address: Center for Microbial Ecology, Michigan State
University, East Lansing, MI 48824-1325.
Present address: USDA-ARS New England Plant, Soil and Water Lab,
University of Maine, Orono, ME 04469.
§
Present address: Department of Biological Sciences, Marshall
University, Huntington, WV 25755-2580.
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