Journal of Bacteriology, April 2000, p. 1930-1934, Vol. 182, No. 7
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
andDepartments of Microbiology and Molecular Genetics and Medicine, University of California, Irvine, Irvine, California 92697
Received 26 August 1999/Accepted 6 January 2000
The free-living spirochete Spirochaeta aurantia was
nearly as susceptible to diacetyl chloramphenicol, the product of
chloramphenicol acetyltransferase, as it was to chloramphenicol itself.
This unexpected susceptibility to diacetyl chloramphenicol was wholly
or partly the consequence of intrinsic carboxylesterase activity, as
indicated by high-performance liquid chromatography, thin-layer
chromatography, and microbiological assays. The esterase converted the
diacetate to chloramphenicol, thus inhibiting spirochete growth. The
esterase activity was cell associated, reduced by proteinase K,
eliminated by boiling, and independent of the presence of either
chloramphenicol or diacetyl chloramphenicol. S. aurantia
extracts also hydrolyzed other esterase substrates, and two of these,
-napthyl acetate and 4-methylumbelliferyl acetate, identified an
esterase of approximately 75 kDa in a nondenaturing gel.
Carboxylesterases occur in Streptomyces species, but in
this study their activity was weaker than that of S. aurantia. The S. aurantia esterase could reduce the
effectiveness of cat as either a selectable marker or a
reporter gene in this species.
Present address: Tuberculosis Research Laboratory (151), Veterans
Administration Medical Center, Long Beach, CA 90822.
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