This Article Full Text Full Text (PDF) Other Versions of this Article: JB.00083-07v1 189/16/5839    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Champion, K. Articles by Higgins, N. P. Search for Related Content PubMed PubMed Citation Articles by Champion, K. Articles by Higgins, N. P.

Growth Rate Toxicity Phenotypes and Homeostatic Supercoil Control Differentiate Escherichia coli from Salmonella enterica Serovar Typhimurium ^,

Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, Alabama 35294-0024

Received 16 January 2007/ Accepted 19 March 2007

Escherichia coli and Salmonella enterica serovar Typhimurium share high degrees of DNA and amino acid identity for 65% of the homologous genes shared by the two genomes. Yet, there are different phenotypes for null mutants in several genes that contribute to DNA condensation and nucleoid formation. The mutant R436-S form of the GyrB protein has a temperature-sensitive phenotype in Salmonella, showing disruption of supercoiling near the terminus and replicon failure at 42°C. But this mutation in E. coli is lethal at the permissive temperature. A unifying hypothesis for why the same mutation in highly conserved homologous genes of different species leads to different physiologies focuses on homeotic supercoil control. During rapid growth in mid-log phase, E. coli generates 15% more negative supercoils in pBR322 DNA than Salmonella. Differences in compaction and torsional strain on chromosomal DNA explain a complex set of single-gene phenotypes and provide insight into how supercoiling may modulate epigenetic effects on chromosome structure and function and on prophage behavior in vivo.

Published ahead of print on 30 March 2007.

Supplemental material for this article may be found at http://jb.asm.org/.