498
MARY BELLE ALLEN
The mold Sportrichium carnis will grow at —10° (68); as will
Choetostylum and Hormodendrum (69); Chdosporium will grow and
complete its life cycle at —7.8°. Development of bacteriophage in cryophilic bacteria was observed by Elder and Tanner (70).
Growth at subzero temperatures often leads to morphological changes
in microorganisms. On return to normal temperatures the usual morphology is re-established (66, 71).
No examples are known of organisms which develop better at subzero temperatures than in the normal temperature range. As noted above,
forms which can grow at exceptionally low temperatures usually do
better at slightly higher ones. Their adaptation merely allows them to
endure better the damaging effects of cold. These may include the
formation of ice in and around cells, structural alterations in the protoplasm, and accumulation of toxic products due to decreased solubility
of many compounds in the surrounding medium or to differential slowing of metabolic reactions, with consequent build-up of intermediates.
The activation energy of some enzyme reactions changes markedly
around 0° (2). In plants, low temperatures may cause a water and salt
imbalance because of their effect on transpiration (12, 72).
Increased cold resistance has been associated by Precht (12) with
an increase in the osmotic concentration of the cell contents, a decrease
of free water and an increase in bound water within the cell, and a
decrease in the permeability of the cell membrane. Not all of these
effects are necessarily associated with a particular case of cold resistance.
The primary consideration is that freezing of the cell contents be prevented. It may be noted that the same adaptations confer on the organism an increased resistance to drying. For relevant literature on the
relation between cold injury and dehydration cf. Luyet and Gehenio
(73).
The surrounding medium greatly affects the ability of microorganisms to develop at low temperatures. Inorganic ions have been reported
to increase cold resistance of yeast in the order Li
growth at low temperatures (75, 76, 77). Colloids in the medium play an
important role in increasing cold resistance (74, 75, 78, 79, 80). Foodstuffs are thus favorable media for low-temperature growth of microorganisms.
B. THERMOPHILS
Considerably more biochemical interest has been attracted by those
organisms which have the ability, and in some cases the necessity, to
live at temperatures which result in the death of other forms of life. All
MARY BELLE ALLEN
The mold Sportrichium carnis will grow at —10° (68); as will
Choetostylum and Hormodendrum (69); Chdosporium will grow and
complete its life cycle at —7.8°. Development of bacteriophage in cryophilic bacteria was observed by Elder and Tanner (70).
Growth at subzero temperatures often leads to morphological changes
in microorganisms. On return to normal temperatures the usual morphology is re-established (66, 71).
No examples are known of organisms which develop better at subzero temperatures than in the normal temperature range. As noted above,
forms which can grow at exceptionally low temperatures usually do
better at slightly higher ones. Their adaptation merely allows them to
endure better the damaging effects of cold. These may include the
formation of ice in and around cells, structural alterations in the protoplasm, and accumulation of toxic products due to decreased solubility
of many compounds in the surrounding medium or to differential slowing of metabolic reactions, with consequent build-up of intermediates.
The activation energy of some enzyme reactions changes markedly
around 0° (2). In plants, low temperatures may cause a water and salt
imbalance because of their effect on transpiration (12, 72).
Increased cold resistance has been associated by Precht (12) with
an increase in the osmotic concentration of the cell contents, a decrease
of free water and an increase in bound water within the cell, and a
decrease in the permeability of the cell membrane. Not all of these
effects are necessarily associated with a particular case of cold resistance.
The primary consideration is that freezing of the cell contents be prevented. It may be noted that the same adaptations confer on the organism an increased resistance to drying. For relevant literature on the
relation between cold injury and dehydration cf. Luyet and Gehenio
(73).
The surrounding medium greatly affects the ability of microorganisms to develop at low temperatures. Inorganic ions have been reported
to increase cold resistance of yeast in the order Li
growth at low temperatures (75, 76, 77). Colloids in the medium play an
important role in increasing cold resistance (74, 75, 78, 79, 80). Foodstuffs are thus favorable media for low-temperature growth of microorganisms.
B. THERMOPHILS
Considerably more biochemical interest has been attracted by those
organisms which have the ability, and in some cases the necessity, to
live at temperatures which result in the death of other forms of life. All