502
MARY BELLE ALLEN
Van Halteren (173) has shown that yeast is protected against the
effects of heat by concentrated solutions of various substances. Yeast
heated for one hour at 44° in the presence of 1 or 2 M NaCl, 1, 2, or 3
M glucose, or 30% sucrose showed little, if any, decrease in respiration
and was able to assimilate nitrogen immediately on being returned to
37°. On the other hand, yeast heated in a dilute medium containing
glucose, minerals, and succinate buffer had a reduced oxygen uptake and
nitrogen assimilation did not proceed for several hours after the period
of heating.
The medium may increase heat resistance by providing conditions for
active metabolism, so that the organisms are better able to repair the
damage done by heat, it may aid growth at high temperatures because
it contains substances which protect proteins from thermal denaturation, or it may affect the water relations of the cell. The first effect may
readily be observed with thermophilic bacteria of the B. subtilis group.
Unless these bacteria are placed in an environment which permits active metabolism, their thermal resistance is not noticeably greater than
that of analogous mesophilic organisms (4, 5).
As to the second possibility, i.e., the effects of sugars, neutral salts,
and indifferent proteins in preventing enzyme inactivation, Virtanen
(174) found that the proteinase of Ps. fluorescens is not inactivated by
10-minutes boiling in a medium containing additional soluble protein,
but is readily destroyed at 60° in a protein-free medium. Bacterial
lipases behaved similarly. Maas (175) found that a mutant of E. colt
which requires pantothenic acid for growth above 30° contained an
extraordinarily thermolabile pantothenate-synthesizing enzyme. This
enzyme was rapidly inactivated even at 25°, but could be protected by
sugars or neutral salts.
There are some indications of an effect of divalent ions on thermal
resistance. The decrease in growth factor requirements of some thermophilic sporeformers in media containing relatively high concentrations
of Ca or Mg ions is suggestive of a protective effect. Bacterial spores,
the most thermoresistant living objects known, have a high Ca content
(176). Calcium has been observed to increase the thermal resistance
of Paramecium (177). The bacteriophages of E. colt, which are notably
thermoresistant in a suitable medium (178) are very sensitive to the
effects of heat unless divalent ions are present in the medium (179).
Although exceptions are known, most organisms which live at
high temperatures are small in size, at least in the sense of having
slender cells, and a high surface/volume ratio. Several years ago
Lamanna (ISO) pointed out that size decreases as temperature range
for growth rises in the genus Bacillus. A survey of the members of the
MARY BELLE ALLEN
Van Halteren (173) has shown that yeast is protected against the
effects of heat by concentrated solutions of various substances. Yeast
heated for one hour at 44° in the presence of 1 or 2 M NaCl, 1, 2, or 3
M glucose, or 30% sucrose showed little, if any, decrease in respiration
and was able to assimilate nitrogen immediately on being returned to
37°. On the other hand, yeast heated in a dilute medium containing
glucose, minerals, and succinate buffer had a reduced oxygen uptake and
nitrogen assimilation did not proceed for several hours after the period
of heating.
The medium may increase heat resistance by providing conditions for
active metabolism, so that the organisms are better able to repair the
damage done by heat, it may aid growth at high temperatures because
it contains substances which protect proteins from thermal denaturation, or it may affect the water relations of the cell. The first effect may
readily be observed with thermophilic bacteria of the B. subtilis group.
Unless these bacteria are placed in an environment which permits active metabolism, their thermal resistance is not noticeably greater than
that of analogous mesophilic organisms (4, 5).
As to the second possibility, i.e., the effects of sugars, neutral salts,
and indifferent proteins in preventing enzyme inactivation, Virtanen
(174) found that the proteinase of Ps. fluorescens is not inactivated by
10-minutes boiling in a medium containing additional soluble protein,
but is readily destroyed at 60° in a protein-free medium. Bacterial
lipases behaved similarly. Maas (175) found that a mutant of E. colt
which requires pantothenic acid for growth above 30° contained an
extraordinarily thermolabile pantothenate-synthesizing enzyme. This
enzyme was rapidly inactivated even at 25°, but could be protected by
sugars or neutral salts.
There are some indications of an effect of divalent ions on thermal
resistance. The decrease in growth factor requirements of some thermophilic sporeformers in media containing relatively high concentrations
of Ca or Mg ions is suggestive of a protective effect. Bacterial spores,
the most thermoresistant living objects known, have a high Ca content
(176). Calcium has been observed to increase the thermal resistance
of Paramecium (177). The bacteriophages of E. colt, which are notably
thermoresistant in a suitable medium (178) are very sensitive to the
effects of heat unless divalent ions are present in the medium (179).
Although exceptions are known, most organisms which live at
high temperatures are small in size, at least in the sense of having
slender cells, and a high surface/volume ratio. Several years ago
Lamanna (ISO) pointed out that size decreases as temperature range
for growth rises in the genus Bacillus. A survey of the members of the