Filament formation in radio-resistant mutants of Escherichia coli S after treatment with ultraviolet light and radiomimetic agents

Growth, reproduction, and death rates of Escherichia coli at increased hydrostatic pressures

ZoBell, Claude E. (University of California, La Jolla) and Andre B. Cobet. Growth, reproduction, and death rates of Escherichia coli at increased hydrostatic pressures. J. Bacteriol. 84:1228-1236. 1962.-Pressures ranging from 100 to 500 atm were found to retard the growth and reproduction of Escherichia coli in nutrient medium. Reproduction (as manifested by cell division or an increase in the number of viable cells) was retarded more than was growth (as manifested by increase in cell size or the formation of biomass). When incubated near the threshold of pressure tolerance (about 475 atm at 30 C), some cells of E. coli grew into long slender filaments showing little evidence of fission or cell division. Compression prolonged the lag phase of E. coli in nutrient medium, particularly at pressures higher than 400 atm. The inhibiting effects of pressure on reproduction and growth were found to be less at 30 than at 20 or 40 C. Pressures of 400 to 1,000 atm accelerated the death rate of E. coli cultures in nutrient medium. The lethal effects of pressure were greater at 40 than at 30 C and greater at 30 than at 20 C.

FILAMENT FORMATION BY ESCHERICHIA COLI AT INCREASED HYDROSTATIC PRESSURES

ZoBell, Claude E. (University of California, La Jolla), and Andre B. Cobet. Filament formation by Escherichia coli at increased hydrostatic pressures. J. Bacteriol. 87:710-719. 1964.-The reproduction as well as the growth of Escherichia coli is retarded by hydrostatic pressures ranging from 200 to 500 atm. Reproduction was indicated by an increase in the number of cells determined by plating on EMB Agar as well as by direct microscopic counts. Growth, which is not necessarily synonymous with reproduction, was indicated by increase in dry weight and protein content of the bacterial biomass. At increased pressures, cells of three different strains of E. coli tended to form long filaments. Whereas most normal cells of E. coli that developed at 1 atm were only about 2 mu long, the mean length of those that developed at 475 atm was 2.93 mu for strain R(4), 3.99 mu for strain S, and 5.82 mu for strain B cells. Nearly 90% of the bacterial biomass produced at 475 atm by strain B was found in filaments exceeding 5 mu in length; 74.7 and 16.4% of the biomass produced at 475 atm by strains S and R(4), respectively, occurred in such filaments. Strain R(4) formed fewer and shorter (5 to 35 mu) filaments than did the other two strains, whose filaments ranged in length from 5 to >100 mu. The bacterial biomass produced at all pressures had approximately the same content of protein and nucleic acids. But at increased pressures appreciably more ribonucleic acid (RNA) and proportionately less deoxyribonucleic acid (DNA) was found per unit of biomass. Whereas the RNA content per cell increased with cell length, the amount of DNA was nearly the same in long filaments formed at increased pressure as in cells of normal length formed at 1 atm. The inverse relationship between the concentration of DNA and cell length in all three strains of E. coli suggests that the failure of DNA to replicate at increased pressure may be responsible for a repression of cell division and consequent filament formation.

Radiomimetic properties of 2-amnipurine in Escherichia coli

Zampieri, Antonio (Palo Alto Medical Research Foundation, Palo Alto, Calif.), and Joseph Greenberg. Radiomimetic properties of 2-aminopurine in Escherichia coli. J. Bacteriol. 91:1773-1774. 1966.-A radioresistant mutant (R(4)) of Escherichia coli strain S was found to be resistant to 2-aminopurine. The composition of the post-treatment plating medium and temperature of incubation did not influence the sensitivity of R(4) to 2-aminopurine. However, strain S was much more sensitive to 2-aminopurine when plated on tryptone-agar than on minimal glucose-salts-agar. Strain S was also more sensitive when the post-treatment incubation was at 37 C than at 45 C. When E. coli strain S was treated with sufficient 2-aminopurine to permit only 10(-5) survivors, 67% of the survivors were resistant to ultraviolet light and to radiomimetic compounds. 2-Aminopurine induced filaments in radiation-sensitive, but not radiation-resistant, strains of E. coli. It is concluded that 2-aminopurine, a base analogue which induces transition mutations, is radiomimetic in several properties.

Nature of the Excitatory Sarcoplasmic Reticular Junction

The appositional regions between the surface membrane and sarcoplasmic reticulum in insects, decapod crustaceans, and barnacles are largely diadic and show a four-layered structure which is roughly circular in surface view. Each consists of the 56-angstrom double-membrane of the in-termediary (here called excitatory) element, and the 75-A double-membrane of the cisternal element of the reticulum, separated by a space of about 100 A. A sheet of electron-dense material is found between the two elements, giving the superficial appearance of an additional membrane. The orbits of thin filaments around the thick filaments adjacent to both excitatory and reticular elements are incomplete on the contact side. Regularly spaced bridges connect the thick filaments with both the excitatory elements and cisternal elements and hold the diads in place during stretch and contraction.

SOME PHYSIOLOGICAL ASPECTS OF MUTANTS OF ESCHERICHIA COLI RESISTANT TO GAMMA IRRADIATION

The gamma irradiation resistant mutants of Escherichia coli were indole negative. They did not produce mucoid or slime material in Endo"s agar. A marked variation was noted in the rates of growth of the resistant mutants under shaking and stationary conditions of culture. The mode and rate of utilization of specific carbohydrate substrates by a strain highly resistant to gamma irradiation (12γ) differed from that of the parent (P) strain. The 12γ resting cell suspensions exhibited no respiration on lactose, but substantial activity on glucose and succinic acid. The DNA and RNA contents per parent and 12γ cell were the same. The possible sites of inactivation are discussed.

RESISTANCE AND CROSS RESISTANCE OF ESCHERICHIA COLI S MUTANTS TO THE RADIOMIMETIC AGENT NITROFURAZONE

Woody-Karrer, Pearl (Palo Alto Medical Research Foundation, Palo Alto, Calif.) and Joseph Greenberg . Resistance and cross resistance of Escherichia coli S mutants to the radiomimetic agent nitrofurazone. J. Bacteriol. 85: 1208–1216. 1963.—Cross-resistance relationships are described for 73 mutants of Escherichia coli strain S selected in one step for resistance to nitrofurazone. The test agents included ultraviolet radiation, five radiomimetic compounds, and penicillin; 12 different types of mutants could be selected. Two of these were chemoresistant, three were identical to radioresistant types previously isolated by use of other radiomimetic agents, and seven represented previously unobserved radioresistant types. The majority of radioresistant strains did not respond to plating-medium reactivation after ultraviolet radiation, despite the ultraviolet radiation responses of several minority representative strains. The data presented indicate that radioresistance in E. coli S does not involve resistance to most toxic agents; on the other hand, cross resistance to radiomimetic compounds is not restricted to alkylating agents.