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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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