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Journal of Bacteriology, October 2001, p. 5554-5561, Vol. 183, No. 19
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.19.5554-5561.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Extragenic Suppressors of Growth Defects in
msbB Salmonella
Sean R.
Murray,1
David
Bermudes,2
Karim Suwwan
de Felipe,3 and
K. Brooks
Low4,*
Departments of
Biology,1 Molecular Biophysics and
Biochemistry,3 and Therapeutic
Radiology,4 Yale University, New Haven,
Connecticut 06520, and Vion
Pharmaceuticals,2 New Haven, Connecticut 06511
Received 9 April 2001/Accepted 7 May 2001
Lipid A, a potent endotoxin which can cause septic shock, anchors
lipopolysaccharide (LPS) into the outer leaflet of the outer membrane
of gram-negative bacteria. MsbB acylates
(KDO)2-(lauroyl)-lipid IV-A with myristate during lipid A
biosynthesis. Reports of knockouts of the msbB gene
describe effects on virulence but describe no evidence of growth
defects in Escherichia coli K-12 or Salmonella. Our data confirm the general lack of growth defects in msbB E. coli K-12. In contrast, msbB Salmonella enterica
serovar Typhimurium exhibits marked sensitivity to galactose-MacConkey
and 6 mM EGTA media. At 37°C in Luria-Bertani (LB) broth, msbB
Salmonella cells elongate, form bulges, and grow slowly.
msbB Salmonella grow well on LB-no salt (LB-0) agar;
however, under specific shaking conditions in LB-0 broth, many
msbB Salmonella cells lyse during exponential growth and a
fraction of the cells form filaments. msbB Salmonella grow
with a near-wild-type growth rate in MSB (LB-0 containing Mg2+ and Ca2+) broth (23 to 42°C). Extragenic
compensatory mutations, which partially suppress the growth defects,
spontaneously occur at high frequency, and mutants can be isolated on
media selective for faster growing derivatives. One of the suppressor
mutations maps at 19.8 centisomes and is a recessive IS10
insertional mutation in somA, a gene of unknown function
which corresponds to ybjX in E. coli. In
addition, random Tn10 mutagenesis carried out in an
unsuppressed msbB strain produced a set of Tn10
inserts, not in msbB or somA, that correlate
with different suppressor phenotypes. Thus, insertional mutations, in
somA and other genes, can suppress the msbB phenotype.
*
Corresponding author. Mailing address: Radiobiology
Laboratories, Yale University School of Medicine, 333 Cedar St., New
Haven, CT 06520. Phone: (203) 785-2976. Fax: (203) 785-6309. E-mail: brooks.low{at}yale.edu.
Journal of Bacteriology, October 2001, p. 5554-5561, Vol. 183, No. 19
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.19.5554-5561.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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