Phage-host Systems Research Articles

Factors affecting phage-restricting ability in Rhizobium leguminosarum strain L4.

Rhizobiophage [Formula: see text] is modified, by growth in Rhizobium leguminosarum strain L25, to the [Formula: see text] form, which has a low plating efficiency on host strain L4. Alteration of plating efficiency (EOP) was used as a means of studying the nature of phage-restricting ability in L4 cells. Mixed infection involving another phage or the unrestricted form of [Formula: see text] as helper phage increased EOP on L4 up to 200-fold, depending on time and sequence of infection. Multiple (cooperative) infection with [Formula: see text] or sublethal heat treatment of cells increased EOP by about 1000-fold. Growth of cells after they were heated resulted in fairly rapid recovery of restricting ability. Ultraviolet light irradiation of cells induced a lower order of EOP enhancement (7- to 10-fold), and loss and recovery of restricting ability appeared to occur more slowly. Some evidence of an interaction between de-restricting treatments was noted for irradiation and multiple infection. Rapid inactivation of the restricted phage genome after injection was indicated in experiments in which de-restricting treatments were applied belatedly after infection. The results and their implications concerning the nature of restricting ability are compared with those of other phage–host systems.

Bacteriophages of Clostridium saccharoperbutylacetonicum Part III

The three representative HM-phages (HM 2, HM 3 and HM 7) of Clostridium saccharoperbutylacetonicum were used. The adsorption rate of the phages HM 2 and HM 7 on the host bacteria was high, whereas that of the phage HM 3 was lower. The adsorption rates of the phages were maximum at pH 5.9_??_6.6, 30°C. One-step growth experiment was successfully adapted to the phage-host systems of anaerobic bacteria by bubbling pure nitrogen gas into the medium in the growth tube. The growth characteristics of the HM-phages were investigated by using this technique. The minimal latent periods for phages HM 2, HM 3 and HM 7 were about 45, 90 and 120 minutes, respectively. The corresponding average burst sizes were approximately 500, 100 and 20, respectively. The growth of the phages was optimal at pH 6.2, 30_??_33°C. The phages failed to grow at 37°C, although the host bacteria multiplied at that temperature. By using a defined medium, it was found that calcium ion was not essential for the growth of the HM-phages.

GROUP N STREPTOCOCCAL PHAGE LYSIN.

Two stages of phage multiplications, the adsorption-penetration process and the lysis of the host, have recently been largely elucidated. For some time it has been postulated that an enzyme attached to, or contained in, the phage tail is involved in the adsorption process with at least some phage-host systems. Similarly, the earliest discovered effect of a lytic phage, namely the liberation of the mature phage particles (lysis of the host), is due to a lytic enzyme acting on the cell wall. Bronfenbrenner & Muckenfuss (1927) recognized that phage lysates contain a substance other than phage. This ‘ ferment-like ’ substance differed from phage because it only affected dead staphylococci. It was adsorbed to clay filters, inactivated on standing at room temperature, it was more heat labile than phage, and did not diffuse through collodion membranes. This description adequately fits the staphylococcal virolysin (or phage lysin) described by Ralston, Beer, Lieberman & Krueger (1955) which lysed only dead cells, although viable cells were lysed in the presence of the homologous phage. Brown (1956) showed that phage-free lysates of coliphage T, could dissolve cells of Eschterichia coli killed with chloroform, and Koch & Jordan (1957) demonstrated a free enzyme in T, phage lysates. Koch & Dreyer (1958) came to the conclusion that the phage lysin was a lysozyme. This was confirmed by Weidel & Katz (1961) and K,atz & Weidel (1961) who purified both the bound and free coli T, phage enzymes; and Murphy (1960), working on similar lines, found that the bound and free ‘ megaterium ’ enzymes differed only in their pH optima. Halo1 formation was observed by Naylor & Czulak (1956) with a lactic acid streptococcal phage, and by Murphy (1957; 1960) with Bacillus megaterium phage. They found that halos were due to an enzyme affecting the dead cells surrounding the phages without giving complete lysis. Murphy demonstrated that the enzyme was resistant to trypsin, pepsin, DNA-ase and RNA-ase but was inactivated by chymotrypsin. It is possible that the inhibition of a rhizobium phage by chymotrypsin reported by Kleczkowsky & Kleczkowsky (1954) may be due to the inhibition of a similar phage enzyme. Halo formation due to cell-wall lysis differs from the halos observed around plaques of mucoid strains of Escherichia coli by Sertic (1929), and since reported to occur with many other organisms. In these cases the halo is due to an enzyme hydrolysing capsular polysaccharides (Adams & Park, 1956). Other aspects of the action of phage lysin are the ‘nascent’ phage phenomenon and ‘lysis from without’. Nascent phage was first observed by Evans (1934) and shown by Maxted (1957) to be due to an enzyme liberated from the host at the same time as the phage. When some phages, e.g. coliphage T,, are adsorbed to their host

CHARACTERIZATION OF ENTEROCOCCUS BACTERIOPHAGES FROM THE SMALL INTESTINE OF THE RAT.

Rogers, C. G. (University of Wisconsin, Madison) and W. B. Sarles. Characterization of enterococcus bacteriophages from the small intestine of the rat. J. Bacteriol. 85:1378-1385. 1963.-Enterococcus bacteriophages were isolated by an enrichment procedure from the contents of the small intestines of Sprague-Dawley white rats. After purification by single-plaque isolation, the phages were maintained in Tryptose broth by propagation on strains of Streptococcus faecalis var. zymogenes of similar intestinal origin. The presence of two phage strains was suggested from host range studies, and confirmed by antiserum neutralization tests, whereby the bacteriophages were placed in two distinct, but serologically related, groups. When the characteristics of one phage from each group were studied, differences were observed in antigenic properties, as shown by the ability to stimulate antibody production in rabbits, and in single-step growth characteristics. At 32 C, the latent period was 21 min, and the burst size was 88 plaque-forming particles (PFP) for phage 1; and 34 min and 147 PFP for phage 2. The bacteriophages were similar in temperature of inactivation, sensitivity to pH, and in rates of adsorption to host cells (K = about 2 x 10(-9) ml/min at 32 C). In electron micrographs, the viruses were characterized by slightly elongated heads and long tails, and resembled one another closely. The dimensions of the phage particles were similar to those reported for other phage-host systems within the genus Streptococcus.

Biochemical modifications in lysogenic B. megatherium 899 (1) after induction with ultraviolet light

1. 1. The time elapsed between induction of B. megatherium 899 (1) by irradiation with ultraviolet light, and formation of the first intra- and extra-cellular bacteriophages has been measured at 27 and 37°C. The latent period is prolonged by an increase in the inducing dose of ultraviolet light. 2. 2. A study of the biochemical modifications occuring after induction of lysogenic B. megatherium has shown that, concomitant with the residual growth, respiration increases, and ribonucleic acid is synthesized. The synthesis of desoxyribonucleic acid is blocked during approximately the first third of the latent period. Rapid synthesis then commences and continues until the moment of lysis. 3. 3. The biochemical modifications during development of temperate phages in induced lysogenic bacteria have been compared with those found in bacteria infected with virulent phages, which block growth completely. Whereas growth, ribonucleic acid and enzyme synthesis does, or does not, occur, depending on the phage-host system studied, the pattern of desoxyribonucleic synthesis seems to be a common property of all phage-host systems examined heretofore.