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Journal of Bacteriology, May 2000, p. 2387-2392, Vol. 182, No. 9
National Food Research Institute, Ministry of
Agriculture, Forestry and Fisheries, Tsukuba 305-8642, Japan
Received 22 October 1999/Accepted 29 January 2000
Certain Bacillus subtilis strains, such as B. subtilis (natto) starter strains for the manufacture
of natto (fermented soybeans), produce capsular poly-
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
A New IS4 Family Insertion Sequence,
IS4Bsu1, Responsible for Genetic Instability of
Poly-
-Glutamic Acid Production in Bacillus
subtilis

-glutamate
(
PGA). In B. subtilis (natto),
PGA
synthesis is controlled by the ComP-ComA two-component regulatory system and thereby induced at the beginning of the stationary growth
phase. We have found a new insertion sequence (IS), designated IS4Bsu1, in the comP gene of a spontaneous
PGA-negative mutant of B. subtilis (natto)
NAF4. IS4Bsu1 (1,406 bp), the first IS discovered in
B. subtilis, encodes a putative transposase (Tpase) with a
predicted Mr of 34,895 (374 residues) which
displays similarity to the Tpases of IS4 family members.
Southern blot analyses have identified 6 to 11 copies of
IS4Bsu1, among which 6 copies were at the same loci, in the
chromosomes of B. subtilis (natto) strains, including NAF4, three commercial starters, and another three
PGA-producing B. subtilis (natto) strains.
All of the eight spontaneous
PGA
mutants, which were
derived from five independent NAF4 cultures, had a new additional
IS4Bsu1 copy in comP at six different positions within 600 bp of the 5'-terminal region. The target sites of
IS4Bsu1 were determined to be AT-rich 9-bp sequences by
sequencing the flanking regions of IS4Bsu1 in mutant
comP genes. These results indicate that IS4Bsu1
transposes by the replicative mechanism, in contrast to other
IS4 members that use the conservative mechanism, and that
most, if not all, of spontaneous
PGA
mutants appear to
have resulted from the insertion of IS4Bsu1 exclusively
into comP. The presence of insertion hot spots in comP, which is essential for
PGA synthesis, as well as
high transposition activity, would account for the high frequency of
spontaneous
PGA
mutation by IS4Bsu1 in
B. subtilis (natto).
*
Corresponding author. Mailing address: National Food
Research Institute, Kannondai 2-1-2, Tsukuba 305-8642, Japan. Phone: 81-298-38-8075. Fax: 81-298-38-7996. E-mail:
yosifumi{at}nfri.affrc.go.jp.
Present address: Genetic Resource Center, National Institute of
Agrobiological Resources, MAFF, Tsukuba 305-8602, Japan.
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