78
A. SARAGEA ET A L
existence of the PWg highly toxigenic strain should be emphasised. This
strain, isolated from a case in 1896 by Park and Williams, is used as a
high toxin producer throughout the world and all its variants maintained
at different reference centres of the world are still toxigenic and lysogenic
(Maximescu, 1968).
(b) Expression of gene tox. Role of iron in toxin production. The toxf gene is
essential for toxin synthesis, but the expression of gene tox is possible only
in certain C. diphtheriae strains. Even with the PW8 strain, a very high
toxin producer, important variations with regard to toxin were recorded in
different laboratories. Although long recognised, the phenomenon did not
receive a satisfactory explanation until Pappenheimer and Johnson (1936)
showed that inorganic iron concentration in the medium played an important and unexpected role in connection with toxin formation. At a
concentration of about 1OOpg of iron per litre of medium, the peak of
toxin production was reached and further additions, although improving
growth, resulted in a rapid fall of toxin, up to 500 pg of Fe per litre, when
toxin could no longer be demonstrated.
Barksdale (1955) and Barksdale et al. (1961) checked the conditions in
which the tox character may be expressed, and also found that the physiological state of the host bacteria was important. Toxin is synthesised in
high yield only by bacteria with an abnormally low iron content. Thus,
the classic Park Williams 8 strain (PWg) possesses the unusual capacity of
increasing in mass five- to six-fold after depleting its exogenous supply of
iron.
The mechanism by which iron controls toxin production has not yet been
elucidated. Recent evidence (Pappenheimer and Gill, 1973) suggests that
the repressor of the tox gene may be an iron-containing bacterial protein.
I n complex media containing chelating agents, such as phosphorus and
calcium ions, the effect of iron on toxin production was not dramatic. In
Pappenheimer’s refined medium far less iron was needed to repress the
yields of toxin because it did not contain chelating agents. Since then, only
complex media have been used for the commercial production of toxin.
It is thus certain that while the structural information for toxin biosynthesis is now known to be carried by the phage genome (Uchida et al.,
1971), its expression is controlled by the nature and physiological state
of the bacterial host. I n particular, high yields of toxin are only synthesised by lysogenic bacteria with low iron content. Maximescu et al. (1968,
1974a, b) showed that gene tox can be expressed and may induce toxin
also in strains of C. ulcerans and C. ovU, the latter representing a species
which has been associated with infections in sheep (apart from some very
rare exceptions in humans). When any one of these corynebacteria were
A. SARAGEA ET A L
existence of the PWg highly toxigenic strain should be emphasised. This
strain, isolated from a case in 1896 by Park and Williams, is used as a
high toxin producer throughout the world and all its variants maintained
at different reference centres of the world are still toxigenic and lysogenic
(Maximescu, 1968).
(b) Expression of gene tox. Role of iron in toxin production. The toxf gene is
essential for toxin synthesis, but the expression of gene tox is possible only
in certain C. diphtheriae strains. Even with the PW8 strain, a very high
toxin producer, important variations with regard to toxin were recorded in
different laboratories. Although long recognised, the phenomenon did not
receive a satisfactory explanation until Pappenheimer and Johnson (1936)
showed that inorganic iron concentration in the medium played an important and unexpected role in connection with toxin formation. At a
concentration of about 1OOpg of iron per litre of medium, the peak of
toxin production was reached and further additions, although improving
growth, resulted in a rapid fall of toxin, up to 500 pg of Fe per litre, when
toxin could no longer be demonstrated.
Barksdale (1955) and Barksdale et al. (1961) checked the conditions in
which the tox character may be expressed, and also found that the physiological state of the host bacteria was important. Toxin is synthesised in
high yield only by bacteria with an abnormally low iron content. Thus,
the classic Park Williams 8 strain (PWg) possesses the unusual capacity of
increasing in mass five- to six-fold after depleting its exogenous supply of
iron.
The mechanism by which iron controls toxin production has not yet been
elucidated. Recent evidence (Pappenheimer and Gill, 1973) suggests that
the repressor of the tox gene may be an iron-containing bacterial protein.
I n complex media containing chelating agents, such as phosphorus and
calcium ions, the effect of iron on toxin production was not dramatic. In
Pappenheimer’s refined medium far less iron was needed to repress the
yields of toxin because it did not contain chelating agents. Since then, only
complex media have been used for the commercial production of toxin.
It is thus certain that while the structural information for toxin biosynthesis is now known to be carried by the phage genome (Uchida et al.,
1971), its expression is controlled by the nature and physiological state
of the bacterial host. I n particular, high yields of toxin are only synthesised by lysogenic bacteria with low iron content. Maximescu et al. (1968,
1974a, b) showed that gene tox can be expressed and may induce toxin
also in strains of C. ulcerans and C. ovU, the latter representing a species
which has been associated with infections in sheep (apart from some very
rare exceptions in humans). When any one of these corynebacteria were