Chromosome Replication in Salmonella typhimurium

Abstract

The replication of the Salmonella typhimurium chromosome was studied. As with E. coli 15T, replication was sequential. After amino acid starvation, replication proceeded from a unique and heritable region of the chromosome. 5-Bromouracil, when substituted for thymine, did not disturb the sequence of replication nor did it initiate extra replication cycles. By labeling the origin and the terminus of the chromosome with 3Hand "4C-thymine, respectively, it was possible to determine that the rate of chain elongation decreases as the growth rate decreases. No gap in the replication cycle could be observed. The sequential replication of the bacterial chromosome has been demonstrated in Escherichia coli by physical and genetic techniques (1, 4, 8, 11, 13, 14, 18). These studies led to the conclusion that replication is initiated at a unique position on the chromosome. Replication ceases at this locus after starvation for amino acids, which allows a replication cycle to be completed but prevents reinitiation of a new cycle (9; R. Bird and K. G. Lark, in press; B. Wolf et al., Cold Spring Harbor Symp. Quant. Biol., in press). Similar results have been obtained in studies of Bacillus subtilis (2, 17). We extended our previous physical studies of the E. coli chromosome to Salmonella typhimurium. This organism has been demonstrated to form genetic hybrids (19) with the deoxyribonucleic acid (DNA) of E. coli and its physiology has been examined in detail (12). The present study demonstrates that most aspects of chromosome replication in Salmonella and Escherichia are similar. MATERIALS AND METHODS Bacterial strains. Five strains of S. typhimurium were obtained from A. Eisenstark. Strain 1660H is a methionine, arginine, tryptophan, and thymine quadruple auxotrophic mutant. The other Hfr strains (3612, 3613, 3632, and 3660) all require histidine and thymine. Their mating types and growth rates in different media are given in Table 1. E. coli 15T-(557) has been described previously (11, 14). Media and supplements. The organisms were grown with aeration at 37 C in either minimal or Casamino Acids (Difco)

Fundamental principles in bacterial physiology—history, recent progress, and the future with focus on cell size control: a review

“…Later, John Cairns pulse-labelled the DNA of E. coli by [ 3 H] thymine and used autoradiography to directly show that the chromosome is a single-stranded, sequentially replicated molecule and replication of DNA starts from a single origin [117,118]. Independently, other researchers reached the same conclusion by using either radioactive labelling [119][120][121][122][123][124][125][126][127][128][129]130], genomic marker transformed by bacteriophage [131][132][133][134][135][136][137] or bromouracil labeling (5-bromouracil is a nucleobase analog and can be differentiated by density measurement) [138][139][140][141][142].…”

Fundamental Principles in Bacterial Physiology - History, Recent progress, and the Future with Focus on Cell Size Control: A Review

“…bromouracil is a nucleobase analog and can be differentiated by density measurement) [138][139][140][141][142].…”