SMALL-CELL SEGREGANTS FROM A POSSIBLY HOMOZYGOUS DIPLOID STRAIN OF ESCHERICHIA COLI

Abstract

AND RONALD D. HUMPHREY. Smallcell segregants from a possibly homozygous diploid strain of Escherichia coli. J. Bacteriol. 85:801-807. 1963.-Evidence was presented to show that a homozygous possibly diploid strain of Escherichia coli, when grown in a chemically defined medium under the conditions described in this report, will yield small-cell segregants that have haploid characteristics. The segregants have one-half as much deoxyribonucleic acid per cell as the diploid, give exponential survival curves when exposed to X rays, and have fermentative characteristics similar to the original haploid parent strain of the homozygous diploid strain. No detectable changes in surface antigens were associated with the segregation phenomenon. The haploidlike segregants can be converted to the diploid radiation-resistant state by growing them in the presence of camphor vapors.

EFFECT OF HAPLOID OR DIPLOID CONSTITUTION OF ESCHERICHIA COLI ON FORMIC HYDROGENLYASE ACTIVITY

“…The number of ribosomes per cell can influence the rate of protein synthesis (Schaechter, Maaloe, and Kjeldgaard, 1958;Neidhardt and Magasanik, 1960;Schaechter, 1961). Ogg and Zelle (1957) and Ogg and Humphrey (1963) found diploid cells in the stationary period of growth to have approximately twice as much RNA per cell as the haploids. Yet, these latter observations do not rule out the possibility that the ratio of ribosomal RNA to DNA in diploids and haploids is not the same during the period of active growth.…”

“…E. coli 82/r, an adenine-requiring mutant strain described by Anderson (1951), was used as the parent haploid strain. Treatments were applied to 82/r as described by Ogg and Humphrey (1963) to produce possibly diploid and subsequent haploid and diploid strains in the following sequence: 82/r (haploid) -* P6…”