Quantitative Radioautographic Studies on Exponentially Growing Cultures of Escherichia coli

Abstract

Exponentially growing cultures of E. coli were examined by quantitative radioautographic techniques to determine the distribution of labeled DNA, RNA, protein, and cell wall among the progeny cells of successive generations. It was found that DNA is in large structures, non-randomly distributed in the progeny. About one-half of the cells have four such structures and approximately one-half contain these four structures plus four smaller ones. These structures show remarkable stability. Fewer than 3.5 per cent of the large structures break in one division time. Protein, RNA, and cell wall are all distributed randomly among progeny cells. The number of units of each component that show random segregation must be 200 or more.

The Mode of Segregation of the Bacterial Cell Membrane

“…In some Gram-positive bacteria, segregation of the cell wall was semiconservative; (3,4,6,7,15,18), while in Gram-negative bacteria, segregation was dispersive; (5,8,14,16,21).…”

Chromosome partitioning in Escherichia coli

“…Although some of this recombination might involve intrachromosomal events, most of it is presumably due to sister chromatid exchange. It should be noted this recombination would not have been detected by the previously used autoradiographic procedures (47).…”

“…Although bacterial chromosomes seem to be large targets for recombination, sister chromatid exchange is an infrequent event over most of the chromosome. By using autoradiographic procedures, the frequency of sister chromatid exchange was estimated to be approximately 3.5% per generation in cells growing in optimal conditions (47). It might be somewhat higher in other conditions, such as in thymine-requiring K-12 strains growing in rich medium (33).…”

MEMBRANE SYNTHESIS IN BACILLUS SUBTILIS

“…In gram-positive bacteria, there is some evidence that wall structures are conserved during growth (Cole and Hahn, 1962 ;Chung et al ., 1964 ;Briles and Tomasz, 1970) . However, in gram-negative bacteria, there is no evidence that the elements of the surface (May, 1963) or the peptidoglycan (van Tubergen and Setlow, 1961 ;Lin et al ., 1971) are conserved . We do not intend to offer solutions to this problem in this discussion, except to suggest that some internal structure analogous to the eukaryotic mitotic apparatus might be the means whereby the chromosomes are apportioned and whereby the cell measures off the proper site for cell division .…”