ISOLATION AND CHARACTERIZATION OF A LARGE CELL POSSIBLY POLYPLOID STRAIN OF ESCHERICHIA COLI

Abstract

A constantly increasing spectrum of bacterial mutations is under active investigation and the utility of bacterial mutation systems in studies of mutagenesis has been amply demonstrated. Once bacteria were considered to be asexually reproducing organisms, but today at least three distinct mechanisms of gene recombination are known. The last decade has seen the introduction of many new techniques and new ideas into bacterial cytology, and although substantial progress may have resulted, there still is no general agreement as to the detailed structure and composition of the bacterial nucleus (De-Lamater, 1954; Knaysi, 1956; Robinow, 1956). Indeed, an active controversy is in progress concerning the presence or absence of a mitotic cycle similar to that in higher organisms and the organization of the chromatinic material into discrete chromosomes which behave during division as do chromosomes in higher plants and animals. Lederberg et al. (1951) made comparative cytological studies of strains of Escherichia coli K-12 known to be haploid and diploid on the basis of genetic evidence. Although they observed certain characteristic differences in the cytological appearances of the two strains, their preparations did not permit any clear interpretation in terms of doubled chromosomes. A correlation between the ratio of uninucleate and multinucleate E. coli strain B and E. coli strain B/r cells in different portions of the growth curve and the ratio of intact to sectored lactosenegative, ultraviolet induced mutant colonies was observed by Witkin (1951) who also noted a correspondence between the modal number of nuclei per cell in her different samples and the modal size of mutant sector. Her observations 1 This work has been supported jointly by Cornell University and the Atomic Energy Commission through research contract No. AT(30-1)-1244.

COMPARISON OF SPECIES AND VARIETIES OF THE GENUS BACILLUS

“…Thus, the increased amount of DNA between organisms represents an increase in DNA per chromatin body and not an increase in number of chromatin bodies per cell. It is interesting to note that a similar increase in DNA per discrete nuclear body was encountered by Ogg and Zelle (1957) during the derivation of a strain of giant cells of Escherichia coli by treatment with camphor. With this increase Zelle and observed a shift from a single to a multiple hit irradiation survival curve.…”

Genetic Analysis of a Large-Cell, Radiation-Resistant Strain of Escherichia coli

“…Our ratios of macromolecular contents for E. coil P6 to 82/r strains of about 3 for the conjugal recombinants (Table 4) correspond to the values reported by Ogg and Zelle (16). However, Ogg and Humphrey (15) reported smaller ratios of about 2.…”

“…Colonial morphologies were scored with a Steroscopic Wide-Field microscope (Bausch and Lomb Optical Co.) with oblique illumination (16). Cell morphologies and the proportion of double cells in the cultures were determined by phase-contrast microscopy with a model GSL microscope (Carl Zeiss, Inc.).…”

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

“…The rate of fermentation by P6 on a number of carbohydrates was reduced, in comparison with 82/r on the same substrates (Ogg and Zelle, 1957). While studying the mechanism of this reduced rate of fermentation, it was found that when P6 was grown under the special growth conditions described in this report small-cell, smoothcolony-forming segregants appeared in such cultures.…”

“…E. coli 82/r, isolated and described by Anderson (1951), is an adeninerequiring mutant of E. coli B/r. E. coli P6 (a large-cell, possibly homozygous diploid strain) was isolated after exposure of E. coli 82/r to camphor vapors (Ogg and Zelle, 1957). On nutrient agar, E. coli 82/r forms smooth, finely granular colonies, whereas P6 is characterized by colonies with a coarsely granular internal structure.…”