I. GROWTH OF CELLS AFTER INFECTION WITH C PHAGE II. RATE OF GROWTH, PHAGE YIELD, AND RNA CONTENT OF CELLS III. EFFECT OF VARIOUS SUBSTANCES ON GROWTH RATE AND PHAGE PRODUCTION

John H. Northrop ¹ and With the Technical Assistance of Marie King

¹ From the Laboratories of The Rockefeller Institute for Medical Research, Department of Bacteriology, University of California, Berkeley

I. Lysogenic B. megatherium 899a (de Jong, 1931) produces two types of phage (Gratia, 1936 c) T and C. The T phage forms cloudy plaques and gives rise to fresh lysogenic strains (Gratia, 1936 b) when added to the sensitive strain of megatherium. It may or may not cause lysis, depending on the media (Northrop, 1951). The C phage occurs very rarely) forms clear plaques, does not give rise to lysogenic strains, and causes complete lysis of the sensitive strain under all conditions tested, provided infection occurs. If C phage is added to the sensitive strain, and the mixture allowed to stand, or made into a hanging drop preparation, the infected cells stop growing and lyse completely after 60 to 80 minutes with the liberation of from 50 to 200 phage particles per cell.

If, however, C phage is added to a rapidly growing culture of B. megatherium and the suspension shaken at 34°, the cells continue to grow and divide for 50 to 60 minutes, after infection has occurred. They then lyse, with the liberation of from 1000 to 2500 phage particles per cell.

II. The following determinations have been made on megatherium sensitive cells growing in 5 per cent peptone at different stages of growth. (1) Growth rate of infected and uninfected cells; (2) RNA, DNA, and protein content; (3) volume of the cell; (4) phage yield per cell by plaque count; (5) phage yield per cell by cell and plaque count; (6) lysis time.

The growth rate decreases as the cell concentration increases.

The lysis time and the protein N per cell are nearly independent of the growth rate; all the other values increase as the growth rate increases.

The ratio

See PDF for Equation

is nearly constant.

RNA and DNA per cell increase less rapidly than the volume, so that NA per unit volume is not constant, but decreases as the size of the cell increases.

The phage yield measured under conditions in which the infected cells do not grow (by plaque count) is very nearly proportional to the size of the cell.

The phage yield per cell, under conditions in which the infected cells do grow, increases more rapidly than the size of the cells.

The phage yield per cell under these conditions may be calculated by the equation

See PDF for Equation

The determining factor for the variation in phage yield is the growth rate of the cells. This, in turn, is determined by the composition of the medium.

III. The growth and phage production of megatherium 899a have been determined in the presence of the following substances: aureomycin, bacitracin, chloromycetin, gramicidin, Merck AB631, Merck AB191, Merck AB624, penicillin, streptomycin, terramycin, tyrothricin, usnic acid, acetone, chloroform, ethyl alcohol, formaldehyde, gentian violet, glycerin, maleic hydrazide, methyl alcohol, phenyl mercuric acetate, sodium fluoride, sulfanilamide, toluene, and urethane. In every case, the lowest concentration of the substance which completely inhibits growth, is also the lowest concentration which completely inhibits phage production.

One antibiotic, Merck AB81, causes increased phage production in concentrations which partially inhibit growth, and low phage production in concentrations which completely inhibit growth (as determined by turbidity).

Short exposure to ultraviolet light also decreases the growth rate, with increase in phage production. Longer exposure, which completely inhibits growth (as determined by turbidity) results in lysis and phage liberation.

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