Efficiency of induction of Shiga-toxin lambdoid prophages in Escherichia coli due to oxidative and antibiotic stress depends on the combination of prophage and the bacterial strain

In the study presented here, we tested, how large a fraction of lysogenic culture was undergoing filamentation, which could indicate triggering of the SOS response or SOS-independent prophage induction that is also known to cause cell filamentation. Here, antibiotic stress was triggered by adding mitomycin C and oxidative stress was induced by hydrogen peroxide. Observation of bacterial cells under an optical microscope revealed more filamenting cells for lysogenic Escherichia coli than for strains not carrying a prophage. Moreover, the amount of filamenting cells depended not only on the stress agents used and the type of the prophage, but also on the host. During induction of the 933W prophage, the resulting phage titer and the amount of elongating cells were different when using E. coli O157:H7 EDL933 clinical isolate and the E. coli MG1655 laboratory strain. The amount of filamenting cells correlates well with the observed phage titers.

Isolation of nonlysogenic bacteria from λ-lysogenized strains using antibiotic-resistant phage

A simple and efficient method for obtaining nonlysogenic bacteria from λ-lysogenized strains using phage with an inserted antibiotic-resistant plasmid is described. When the lysogenic culture is infected with antibiotic-resistant phage, single non-lysogenic cells are lysogenized, isolated on selective medium, and cured of phage during incubation at 37 °C.

Morphological Characterization of Mycobacteriophage R1

Mycobacteriophage R1 was originally isolated from a lysogenic culture of M. butyricum. The virus was propagated on a leucine-requiring derivative of M. smegmatis, 607 leu−, isolated by nitrosoguanidine mutagenesis of typestrain ATCC 607. Growth was accomplished in a minimal medium containing glycerol and glucose as carbon source and enriched by the addition of 80 μg/ ml L-leucine. Bacteria in early logarithmic growth phase were infected with virus at a multiplicity of 5, and incubated with aeration for 8 hours. The partially lysed suspension was diluted 1:10 in growth medium and incubated for a further 8 hours. This permitted stationary phase cells to re-enter logarithmic growth and resulted in complete lysis of the culture.

THE ROLE OF TEMPERATE BACTERIOPHAGE IN THE PRODUCTION OF ERYTHROGENIC TOXIN BY GROUP A STREPTOCOCCI

Non-lysogenic, non-toxinogenic Group A streptococci when infected by temperate bacteriophages isolated from known scarlatinal toxin-producing strains acquire the capacity to form erythrogenic toxin. This toxin causes a characteristic erythematous reaction in the skin of rabbits and is readily neutralizable by standard scarlatinal antitoxins. The production of toxin appears to be related to the synthesis of mature phage particles since ultraviolet enhancement of phage production results in a concomitant increase in toxin titer. In contrast, there is no increase in the production of another extracellular product, deoxyribonuclease, by these lysogenized streptococci. Furthermore, cellular disruption studies indicate that the toxin probably does not exist in a preformed state within the cell. Double diffusion reactions in agar indicate that a newly formed protein appears in the lysogenic culture filtrate and is absent in the non-lysogenic filtrates.

NUCLEIC ACID SYNTHESIS BY A LYSOGENIC STRAIN OF ESCHERICHIA COLI INFECTED WITH ANrII MUTANT OF COLIPHAGE T2

Mutants of phage T2, of the group called rII mutants, are known to lack the parent phage's ability to form plaques on strains of Escherichia coli lysogenic for phage λ That they are capable of initiating desoxyribonucleic acid synthesis in the infected lysogenic host cells but are incapable of maintaining it has been shown by the present study using T2r7and -E. coli C112 (λs). In contrast with the superficially similar behavior shown by some other phages (e.g. λv1h), ultraviolet irradiation and consequent induction of the lysogenic culture do not release the prophage-linked inhibition of T2r7DNA synthesis. Net ribose-nucleic acid synthesis is stopped in all cultures on infection with T2r7.

618. Host-phage relationship of cheese starter organisms: I. Interaction of phage races with a strain of Streptococcus lactis and its lysogenic and resistant derivatives

A lysogenic culture, prepared in the laboratory from a strain of Streptococcus lactis, was used as a cheese starter in commercial factories. It was attacked in turn by two other unrelated phage races. The lysogenic condition, which involved slight morphological and physiological changes, persisted in the subsequent forms resistant to one or both the new phage races. Acquired resistance to any one of the three phages did not protect the culture from the other two phages.In nature such interactions between phage races and lactic acid bacteria must be constantly taking place, giving rise to similarly related strains.Two of the three phage races produced spreading haloes around their plaques due to a lysin released during phage action. The lysin may also interfere with the survival of secondary growth after attack by these phage races. Production of this type of lysin is thus a property of the phage race and not of the bacterial strain.

THE B. MYCOIDES N HOST-VIRUS SYSTEM

Experiments were performed to determine the mechanism of release of phage from the lysogenic strain of B. mycoides N. The results suggest that qualitatively the same situation obtains as in the phage-carrying cultures of B. megatherium 899 and E. coli Li; i.e., the population consists of two kinds of cells: "lysogènes potentiels" and "producteurs." Quantitatively, however, there are more "producers" in a broth culture of the lysogenic B. mycoides N, at least curing the first 4 to 8 hours after cells have been suspended in fresh medium, suggesting that the interaction between host and parasite is one in which the balance is easily swung in favor of the virus. These conclusions are based upon the following lines of evidence: (1) the slow "growth rate" of the lysogenic culture, (2) the fact that the colony count falls far below the plaque count or the filament count (which correspond) for a well washed suspension, (3) the increase in phage output in a large number of tubes, each containing a small number of lysogenic cells, after a few hours' incubation in nutrient broth at 30°C.

GROWTH AND PHAGE PRODUCTION OF LYSOGENIC B. MEGATHERIUM

Cell multiplication and phage formation of lysogenic B. megatherium cultures have been determined under various conditions and in various culture media. 1. In general, the more rapid the growth of the culture, the more phage is produced. No conditions or culture media could be found which resulted in phage production without cell growth. 2. Cultures which produce phage grow normally, provided they are shaken. If they are allowed to stand, those which are producing phage undergo lysis. Less phage is produced by these cultures than by the ones which continue to grow. 3. Cells plated from such phage-producing cultures in liquid yeast extract medium grow normally on veal infusion broth agar or tryptose phosphate broth agar, which does not support phage formation, but will not grow on yeast extract agar. 4. Any amino acid except glycine, tyrosine, valine, leucine, and lysine can serve as a nitrogen source. Aspartic acid gives the most rapid cell growth. 5. The ribose nucleic acid content is higher in those cells which produce phage. 6. The organism requires higher concentrations of Mg, Ca, Sr, or Mn to produce phage than for growth. 7. The lysogenic culture can be grown indefinitely in media containing high phosphate concentrations. No phage is produced under these conditions, but the cells produce phage again in a short time after the addition of Mg. The potential ability to produce phage, therefore, is transmitted through cell division. 8. Colonies developed from spores which have been heated to 100°C. for 5 minutes produce phage and hence, infected cells must divide. 9. No phage can be detected after lysis of the cells by lysozyme.