11. ORGANISMS AND THERMAL ENERGY
501
thermophily usually involves selection of mutants rather than gradual
adaptation of a population. Kluyver and Baars used large inocula in
their experiments, and those of Allen were designed for mutant selection. A number of attempts which have been made to increase the
temperature range for growth of bacterial cultures by gradual adaptation have been unsuccessful (88, 165). Sobotka et al. (166) have recently used the selection principle to obtain soil bacteria with exceptionally high temperature maxima.
IV. Methods of Protection against the Destructive Effects of
Thermal Energy
The destructive effects of thermal energy are most apparent in the
upper portion of the biokinetic temperature range, and the means of
protection against such effects are often most clearly illustrated by the
thermophilic microorganisms. The external environment of the cells,
structural features of the organisms, including structural modifications
on a molecular level, and dynamic effects of metabolism in preventing
or repairing thermal damage all play a part in permitting these organisms to contend with high temperatures.
As with cold resistance, the thermal resistance of microorganisms depends upon the environment in which they are placed; the most obvious
example of this being the well known fact that bacteria in a dry condition can survive heat which is lethal when they are wet. Examples indicating an effect of the chemical composition of growth media upon the
heat resistance of organisms are readily found. Nakamura (167) in
1897 reported that beer yeast, which completely lost its ability to ferment on heating for 30 minutes at 50° in water or 10% sucrose solution,
retained its fermenting ability if heated in a sugar solution containing
the minerals necessary for growth, or in meat extract. The ability to reproduce was lost in all cases. Göbel (168) obtained greater survival of
Fseudomonas aeruginosa in bouillon than in physiological salt solution
when the two suspensions were exposed to the same elevated temperature. Richet et al. (169) increased the maximum growth temperature of
a lactic acid bacterium from 36-37° to 41-42° by cultivation in the
presence of 3.4% KC1.
Although Casman and Rettger (165) failed to find any protective
effect of hypertonic solutions on a number of organisms of the B. subtilis
group, Baumgartner (170, 171) reported that 0.5 M solutions of glucose, galactose, lactose, maltose, sucrose, glycerol, and mannitol protected E. colt from thermal destruction. Anderson et al. (172) found
that glucose and sucrose increased the heat resistance of B. coagulans,
while NaCl and several organic acids decreased it.
501
thermophily usually involves selection of mutants rather than gradual
adaptation of a population. Kluyver and Baars used large inocula in
their experiments, and those of Allen were designed for mutant selection. A number of attempts which have been made to increase the
temperature range for growth of bacterial cultures by gradual adaptation have been unsuccessful (88, 165). Sobotka et al. (166) have recently used the selection principle to obtain soil bacteria with exceptionally high temperature maxima.
IV. Methods of Protection against the Destructive Effects of
Thermal Energy
The destructive effects of thermal energy are most apparent in the
upper portion of the biokinetic temperature range, and the means of
protection against such effects are often most clearly illustrated by the
thermophilic microorganisms. The external environment of the cells,
structural features of the organisms, including structural modifications
on a molecular level, and dynamic effects of metabolism in preventing
or repairing thermal damage all play a part in permitting these organisms to contend with high temperatures.
As with cold resistance, the thermal resistance of microorganisms depends upon the environment in which they are placed; the most obvious
example of this being the well known fact that bacteria in a dry condition can survive heat which is lethal when they are wet. Examples indicating an effect of the chemical composition of growth media upon the
heat resistance of organisms are readily found. Nakamura (167) in
1897 reported that beer yeast, which completely lost its ability to ferment on heating for 30 minutes at 50° in water or 10% sucrose solution,
retained its fermenting ability if heated in a sugar solution containing
the minerals necessary for growth, or in meat extract. The ability to reproduce was lost in all cases. Göbel (168) obtained greater survival of
Fseudomonas aeruginosa in bouillon than in physiological salt solution
when the two suspensions were exposed to the same elevated temperature. Richet et al. (169) increased the maximum growth temperature of
a lactic acid bacterium from 36-37° to 41-42° by cultivation in the
presence of 3.4% KC1.
Although Casman and Rettger (165) failed to find any protective
effect of hypertonic solutions on a number of organisms of the B. subtilis
group, Baumgartner (170, 171) reported that 0.5 M solutions of glucose, galactose, lactose, maltose, sucrose, glycerol, and mannitol protected E. colt from thermal destruction. Anderson et al. (172) found
that glucose and sucrose increased the heat resistance of B. coagulans,
while NaCl and several organic acids decreased it.