IV. INVESTIGATION OF C. DIPHTHERZAE
77
The acquisition of these two properties is obligatory for all lysogenic
conversions. In some cases bacteria acquire new properties through
lysogenisation. One of the most striking effects of genotypic modifications
brought about in the cell by lysogenisation is the toxigenic conversion in C.
diphtheriae. By exposing a phage-sensitive, non-toxigenic (tox-) strain to a
filtered lysate of phage B (previously isolated, described and referred to
by Toshach (1950) as phage C/13) Freeman (1951) made the remarkable
discovery that the tox- strain exposed to phage resulted in the outgrowth
of C. diphtheriae toxigenic (tox+) strain. The same change was induced in
countless experiments by various investigators and by ourselves using the
temperate mutant / 3 isolated by Barksdale from phage B in different C.
diphtheriae strains. Similar results were also obtained by using other
temperate bacteriophages. The non-toxigenic strains were always demonstrated as not producing toxin prior to exposure to phage. Passage of the
phage-modified strains through antiphage serum in no way altered the
capacity to produce toxin (Freeman and Morse, 1952). This signified that
the lysogeny and toxigeny were both stable properties. Groman (1955)
succeeded in curing the Cq (p) tox+ strain of its prophage and toxigeny by
superinfection with a virulent mutant of phage p, thus demonstrating that
elimination of prophage from lysogenic toxigenic strains resulted in loss of
toxigenicity .
Later, in analytical experiments, it became obvious that converting
genes are expressed during vegetative replication of phage. Matsuda and
Barksdale (1967) using a virulent mutant of , d were able to obtain yields of
toxin in one cycle of virus growth equal to the best yield of the Pw8 strain.
Corynebacteriophage P-tox+ is a DNA virus. Groman (1955) found a
temperate phage y-tox- which was related to p-toxf and recombinants of
the two were obtained. Holmes and Barksdale (1969, 1970) elaborated a
mating system and achieved the mapping of the tox gene. They showed that
gene toxf is distributed among a considerable variety of corynebacteriophages, differing both serologically and genetically. Thus tox+ occurs even
in phages not closely related to p.
2. The gene tox of corynebacteriophages
(a) Stability of integration of toxprophages. There are toxf and tox- bacteriophages.
Even when the tox+ gene is present in a bacteriophage it cannot always
be expressed. Experiments of skilled workers (Barksdale, 1970) as well as
our own data, obtained during the surveillance of the pathogenic agent,
showed that, irrespective of the method of storing of the organism, prophages and toxigeny are stably integrated and that only in pseudolysogenic
carrier cultures is the loss of toxigeny observed. In this connection the
77
The acquisition of these two properties is obligatory for all lysogenic
conversions. In some cases bacteria acquire new properties through
lysogenisation. One of the most striking effects of genotypic modifications
brought about in the cell by lysogenisation is the toxigenic conversion in C.
diphtheriae. By exposing a phage-sensitive, non-toxigenic (tox-) strain to a
filtered lysate of phage B (previously isolated, described and referred to
by Toshach (1950) as phage C/13) Freeman (1951) made the remarkable
discovery that the tox- strain exposed to phage resulted in the outgrowth
of C. diphtheriae toxigenic (tox+) strain. The same change was induced in
countless experiments by various investigators and by ourselves using the
temperate mutant / 3 isolated by Barksdale from phage B in different C.
diphtheriae strains. Similar results were also obtained by using other
temperate bacteriophages. The non-toxigenic strains were always demonstrated as not producing toxin prior to exposure to phage. Passage of the
phage-modified strains through antiphage serum in no way altered the
capacity to produce toxin (Freeman and Morse, 1952). This signified that
the lysogeny and toxigeny were both stable properties. Groman (1955)
succeeded in curing the Cq (p) tox+ strain of its prophage and toxigeny by
superinfection with a virulent mutant of phage p, thus demonstrating that
elimination of prophage from lysogenic toxigenic strains resulted in loss of
toxigenicity .
Later, in analytical experiments, it became obvious that converting
genes are expressed during vegetative replication of phage. Matsuda and
Barksdale (1967) using a virulent mutant of , d were able to obtain yields of
toxin in one cycle of virus growth equal to the best yield of the Pw8 strain.
Corynebacteriophage P-tox+ is a DNA virus. Groman (1955) found a
temperate phage y-tox- which was related to p-toxf and recombinants of
the two were obtained. Holmes and Barksdale (1969, 1970) elaborated a
mating system and achieved the mapping of the tox gene. They showed that
gene toxf is distributed among a considerable variety of corynebacteriophages, differing both serologically and genetically. Thus tox+ occurs even
in phages not closely related to p.
2. The gene tox of corynebacteriophages
(a) Stability of integration of toxprophages. There are toxf and tox- bacteriophages.
Even when the tox+ gene is present in a bacteriophage it cannot always
be expressed. Experiments of skilled workers (Barksdale, 1970) as well as
our own data, obtained during the surveillance of the pathogenic agent,
showed that, irrespective of the method of storing of the organism, prophages and toxigeny are stably integrated and that only in pseudolysogenic
carrier cultures is the loss of toxigeny observed. In this connection the