The Induction of Lysogenesis in Salmonella typhimurium

Parry, W. R.; Edwards, Joyce

doi:10.1099/00221287-9-2-342

Cited by 2 publications

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“…It has been suggested (Parry & Edwards, 1953) that the decision towards lysogenesis or productive development of the phage turns on the interplay of two factors, namely varying degrees of virulence on the part of the phage particles and varying degrees of resistance to lysis on the part of the bacteria. However, in view of the wide variation in the pattern of lysogenesis and lysis shown by the 11 phages when tested against the same bacterial suspension, it is obvious that under these conditions bacterial resistance plays a secondary role in determining the outcome of phage infection.…”

Section: Discussionmentioning

confidence: 99%

The Type A Phages of Salmonella typhimurium: Observations on Temperate Phage and Lysogenesis

Boyd

Bidwell

1961

Journal of General Microbiology

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SUMMARYWhen a standard suspension of Salmonella typhirnurium Q l , an indicator strain sensitive to the type A phages recovered from lysogenic strains of this organism, was exposed to concentrations of these phages giving a phage:bacteria ratio of approximately 1 : 10 (thus ensuring that, with rare exceptions, bacteria became infected with single phage particles) it was found that definite percentages of the bacteria were either lysogenized or productively infected (lysed). These percentages were constant for each particular phage type, but varied widely in the 11 members of the group. It was concluded that each phage consisted of a mixed population of particles, some capable, as single infections, of producing lysogenization (a particles) and others lacking this property (p particles). An increase in the phage :bacteria ratio, resulting in multiple infections of single bacteria, led to an increase in lysogenization a t the expense of productive infection, The number of a particles present in any particular concentration of phage was calculated from the figures determined at low phage: bacteria ratios (limit dilution). With some phages, when bacteria became infected with more than one particle by exposure to rising phage concentrations, the number lysogenized was compatible with the hypothesis that a particles are dominant over , 8 particles, and that every bacterium infected by an a particle is lysogenized. This hypothesis was however invalidated by the fact that, with other phages, either the number of bacteria lysogenized was in excess of the available a particles, indicating that bacteria had been lysogenized by infection with two or more B particles, or the number of a particles was grossly in excess of the number of bacteria lysogenized. The implications of these findings are discussed.Very high concentrations of these temperate phages produced lysis-from-without, and in some cases appeared to induce lysis of bacteria which had first been lysogenized. In all cases in which such experiments were carried out, exposure to low temperatures ( g o 0 ) , to high temperatures ( 4 2 O ) , to the salts of certain organic acids, and to anaerobiosis had no significant effect on lysogenization.

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Section: Discussionmentioning

confidence: 99%

The Type A Phages of Salmonella typhimurium: Observations on Temperate Phage and Lysogenesis

Boyd

Bidwell

1961

Journal of General Microbiology

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“…These observations and others already mentioned provide undoubted evidence that the physiological state of the bacterium can influence the establishment of lysogenic infection in S. typhi-murium but do not in any way alter the fact that under normal conditions of culture, although infection with a single particle can occasionally produce symbiotic infection, exposure to numerous particles increases the proportion of bacteria which react in this way. Parry & Edwards (1953) suggest that there may be a range of particles having different degrees of virulence and that those of weak lytic ability are dominant over the others and, by establishing symbiosis, protect the bacterium they invade. Alternatively, it has been postulated (Boyd, 1952) that temperate phage may be a mixed brood of particles with different properties.…”

Section: The Establishment Of Symbiotic Infectionmentioning

confidence: 99%

Bacteriophage

Boyd

1956

Biological Reviews

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SUMMARY In the lysogenic bacterium the bacterial virus exists as prophage. It is composed of desoxyribosenucleic acid (DNA) and occupies a defined site on the bacterial chromosome. Normally the prophage divides in harmony with the nucleus of the bacterium, so that lysogenesis is hereditary. Occasionally the prophage reverts from symbiosis to virulence, and multiplies at the expense of its host, producing a brood of free phage particles. This is believed to occur when the prophage becomes detached from the chromosome. Free phage particles may be temperate (capable of reproducing lysogenesis in a sensitive bacterium) or virulent (unable to produce lysogenesis and multiplying only at the expense of the doomed host). Temperate particles greatly outnumber virulent particles, which are in fact mutants. Reasons are given for believing that all virulent phages (such as the T series of coliphages) originate in this way. Free phage particles have a characteristic tadpole‐like structure of varying proportions. The tail and the covering of the head are composed of protein, which has specific antigenic characters. The contents of the head consist of DNA. The protein envelope and tail of the particle are chiefly mechanical in function. The tail adheres to the host bacterium and breaches its covering membrane. The contents of the head are then injected into the bacterium. They constitute the infective element. A temperate phage may produce lysogenesis or may multiply in the same way as a virulent particle. Various factors facilitate or interfere with the establishment of lysogenesis. There is evidence to suggest that some temperate particles are specially endowed to produce lysogenesis, while others can undergo only productive development at the expense of the host. Virulent particles multiply only by productive development. The infecting virus displaces the genetic apparatus of the bacterium and directs the bacterial enzymes to its own ends. The nucleic acid of the bacterium, augmented if necessary by newly synthesized material from the culture medium, is broken down to nucleotide level or lower, and resynthesized into viral DNA. Protein is synthesized separately. Ultimately both are assembled into mature particles. Lysogenic bacteria are immune to the phage they produce, and to allied types. Occasional virulent mutants are exceptions to this rule. In certain cases temperate phage particles transduce genetic characters from one bacterium to another. Bacterial species (the classical example being Salmonella typhi) can be broken down into numerous ‘phage‐types’ by tests which exploit the hereditary immunity conferred by the various symbiotic phages. Alternatively, different races of a bacterial species can be recognized by isolating and identifying the symbiotic phage which they carry.

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The Induction of Lysogenesis in Salmonella typhimurium

Cited by 2 publications

References 1 publication

The Type A Phages of Salmonella typhimurium: Observations on Temperate Phage and Lysogenesis

The Type A Phages of Salmonella typhimurium: Observations on Temperate Phage and Lysogenesis

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