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Applied and Environmental Microbiology, January 2001, p. 82-88, Vol. 67, No. 1
Department of Microbiology and Immunology,
College of Medicine, National Cheng-Kung University, Tainan 701, Taiwan, Republic of China
Received 24 July 2000/Accepted 18 October 2000
We have cloned a nuclease gene, vvn, from Vibrio
vulnificus, an estuarine bacterium that causes wound infections
and septicemia in humans and eels. The gene contained a 696-bp open
reading frame encoding 232 amino acids (aa), including a signal
sequence of 18 aa. The deduced amino acid sequence of the mature
nuclease predicted a molecular mass of 25 kDa, which was confirmed by
vital stain, and a pI of 8.6. Vvn was produced in the periplasm of
either V. vulnificus or recombinant Escherichia
coli strains and was active in the oxidized (but not the reduced)
form. This nuclease was able to digest DNA and RNA, with differential
thermostability in DNase and RNase activities. Expression of Vvn in
E. coli DH5
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.1.82-88.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Cloning and Characterization of a Periplasmic
Nuclease of Vibrio vulnificus and Its Role in Preventing
Uptake of Foreign DNA
reduced the frequencies of transformation
with the divalent ion-treated cells and electroporation by about 6 and
2 logs, respectively. In addition, the transformation frequency of a
Vvn-deficient V. vulnificus mutant (ND) was 10-fold higher
than that of the parent strain. These data suggested that Vvn may be
involved in preventing uptake of foreign DNA by transformation.
However, Vvn expressed in the recipients had little effect on the
conjugation frequency in either E. coli or V. vulnificus. Some other DNase(s) may be present in the periplasm
and responsible for a residual DNase activity, which was about
one-fourth of that of the parent strain, detected in the ND mutant. We
also demonstrated that Vvn was not required for the virulence of
V. vulnificus mice.
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, College of Medicine, National Cheng-Kung University, 1 Ta-Hsieh Rd., Tainan 701, Taiwan, Republic of China. Phone: 886-6-2353535, ext. 5635. Fax: 886-6-2082705. E-mail:
h061453{at}mail.ncku.edu.tw.
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