Studies on the origin of bacterial viruses. I-IV

I. The Incidence of Phage-Producing Cells in Various B. megatherium Cultures Analyses of small samples containing a few cells each show that lysogenic B. megatherium produces phage particles in groups of from 10 to 1000 depending on the megatherium strain and the culture medium. These groups probably correspond to the number of particles produced by a single cell. The proportion of such phage-producing cells varies from <1 x 10(-10) to about 1 x 10(-2) depending on the megatherium strain and the culture medium. If a culture produces two types of phage, the different types usually appear in separate samples. If mixed samples occur, the number of such samples is about what would be expected for the probability that two separate groups would appear in one sample. This result indicates that the appearance of a distinct phage type is the result of a change in the bacterial cell rather than a change in a phage particle, since in the latter case a mixture of the two types would result. II. The Effect of Ultraviolet Light on the Incidence of Phage-Producing and of Terramycin-Resistant Cells in Various B. megatherium Cultures Low intensity of ultraviolet light increases the proportion of both phage-producing cells and of terramycin-resistant mutants. The increase in phage-producing cells is greater than the increase in terramycin-resistant cells. High intensities of ultraviolet light cause practically all the cells of some B. megatherium strains to produce phage. The number of terramycin-resistant mutants cannot be determined under these conditions. The effect of ultraviolet light varies, depending on the megatherium strain and the culture medium. III. The Effect of Hydrogen Peroxide on the Incidence of Phage-Producing and of Terramycin-Resistant Cells in Various B. megatherium Cultures Low concentrations of hydrogen peroxide increase the number of phage-producing cells and of terramycin-resistant cells, concomitantly, from two to five times. High concentrations of hydrogen peroxide cause almost all the cells of some strains of megatherium to produce phage. IV. Calculation of the Incidence of Phage-Producing Cells The time rate of the appearance of phage particles in normal cultures, or in cultures treated with ultraviolet light or hydrogen peroxide, may be calculated by the same equations which predict the occurrence of terramycin-resistant mutants in B. megatherium cultures. These equations predict that the number of mutants will increase more or less in proportion to the concentration of mutagenic agent, so long as the mutation rate remains very small compared to the growth rate. As the mutation rate approaches the growth rate, there will be a very rapid increase in the proportion of mutants. This explains the striking effect of higher concentrations of mutagenic agents. In order to calculate the results after exposure to strong ultraviolet light or hydrogen peroxide, it is necessary to assume that the change from normal to phage-producing cell occurs without cell division.     

Studies on adhesion, haemagglutination and other biological properties of Vibrio cholerae O139

Abstract The adhesive capabilities of eight Vibrio cholerae O139 epidemic strains to isolated rabbit intestinal epithelial cells (RIEC) were observed to be high similar to those observed with a Vibrio cholerae O1 strain isolated from patients. Toxin production by the strains, measured by accumulation of fluid in rabbit ileal loop model, was high and the toxin was lethal as the animal expired within 6 h. Culture filtrates of the strains exhibited the presence of vascular permeability factor which produce induration and necrosis in the adult rabbit and guinea pig skin. All the strains showed high to moderate haemagglutinin titres against chicken erythrocytes and produced El Tor-like haemolysin. SDS-PAGE of the outer membrane preparation of the strains showed the presence of major protein component at 38 kDa region. The lethality of the toxin, high adhesive activity, shifting of the major outer membrane protein band and production of thermolabile haemolysin on Wagatsuma agar were the major variations of these epidemic strains from V. cholerae O1 and V. cholerae non-O1 strains isolated previously.     

Studies on the adaptation of influenza viruses to MDCK cells

The amino acid sequences and biological properties of the haemagglutinin of three variants of the influenza virus X-31 (H3N2) selected for their capacity to grow in MDCK cells are reported. In two variants, amino acid substitutions at HA1 residues 8 and 144 correlated with the loss of a site for glycosylation and specific changes in antigenicity, respectively. In all three variants substitution of an arginine residue for histidine at HA1 position 17 was correlated with increased pH optima of haemolysis. The importance of this substitution for cleavage of the haemagglutinin precursor required to produce infectious virus is discussed in relation to the three-dimensional structure of X-31 haemagglutinin.     

Studies on the spread of certain plant viruses in the field

Studies on the spread of potato viruses X and Y and cucumber mosaic virus in the field are described: tobacco was used as the experimental plant. The plants were set out in the form of a cross, one series with the leaves in contact and one with the leaves not touching. No spread of potato virus X was observed, but there was extremely rapid permeation of virus Y throughout the plots. The spread of cucumber mosaic virus was much slower than that of virus Y.