11. ORGANISMS AND THERMAL ENERGY
499
of these are microorganisms, including blue-green algae, bacteria, actinomycetes, and fungi. The massive development of thermophilic bluegreen algae which occurs in many hot springs early attracted the attention of naturalists, but these photosynthetic thermophils have been the
subjects of few biochemical studies.* The investigation of the physiological and biochemical factors which permit growth at high temperatures has for the most part been carried out with the spore-forming bacteria, which are readily accessible to laboratory study, and which grow
at temperatures at least as high as 85°.
The first thermophilic bacterium was isolated by Miquel (82, 83)
from water of the Seine in 1879. In spite of the cool habitat from which
it was obtained, it was able to grow at 73°, and could not grow at low
temperatures. During the following decades, thermophilic bacteria were
found in almost every sample of soil, mud, or water which was examined. They were isolated not only from tropical soils (84, 85) and
desert sands (86), but also from air (83, 87), freshly fallen snow
(88, 89), sea water (90), and even ocean bottom mud (91). Water
(92-95), sewage (92, 96), feces of man and various animals (83, 90,
97-103), cultivated soils (90, 100, 102, 104-107), and masses of decaying
plant materials (108-115) were especially good sources. The great
majority of the bacteria isolated at high temperatures proved to be
aerobic sporeforming bacteria; nonsporeformers are rare and facultative forms more common than obligate anaerobes, although the latter
are known (116-118).
Mass development of thermophilic bacteria often occurs in tightly
packed masses of plant materials, such as hay or manure piles. In haystacks, for example, high temperatures are likely to develop, even to the
point where the hay spontaneously ignites. This has been shown to be
the result of bacterial action; the rise in temperature is accompanied by
a loss in weight of the hay, and gaseous products and volatile acids are
formed (112,113,119,120).
Alteration of plant material by thermophilic
bacteria is sometimes used in the preparation of certain types of fodder
or manure (121-123).
In general, however, thermophilic bacteria are a nuisance rather than
a help in agricultural and industrial practice. Thermophilic sporeformers are among the principal causes of spoilage of canned foods,
since not only are their vegetative cells adapted to life at elevated
temperatures, but also their spores are unusually heat resistant, some
* The "thermophilic" strains of Chlorella pyrenoidosa which have recently been
reported (81) have a temperature maximum only slightly above 40°. The only
chlorophyte known which can grow at a temperature of 55° is Cyanidium
caldarium
(81a).
499
of these are microorganisms, including blue-green algae, bacteria, actinomycetes, and fungi. The massive development of thermophilic bluegreen algae which occurs in many hot springs early attracted the attention of naturalists, but these photosynthetic thermophils have been the
subjects of few biochemical studies.* The investigation of the physiological and biochemical factors which permit growth at high temperatures has for the most part been carried out with the spore-forming bacteria, which are readily accessible to laboratory study, and which grow
at temperatures at least as high as 85°.
The first thermophilic bacterium was isolated by Miquel (82, 83)
from water of the Seine in 1879. In spite of the cool habitat from which
it was obtained, it was able to grow at 73°, and could not grow at low
temperatures. During the following decades, thermophilic bacteria were
found in almost every sample of soil, mud, or water which was examined. They were isolated not only from tropical soils (84, 85) and
desert sands (86), but also from air (83, 87), freshly fallen snow
(88, 89), sea water (90), and even ocean bottom mud (91). Water
(92-95), sewage (92, 96), feces of man and various animals (83, 90,
97-103), cultivated soils (90, 100, 102, 104-107), and masses of decaying
plant materials (108-115) were especially good sources. The great
majority of the bacteria isolated at high temperatures proved to be
aerobic sporeforming bacteria; nonsporeformers are rare and facultative forms more common than obligate anaerobes, although the latter
are known (116-118).
Mass development of thermophilic bacteria often occurs in tightly
packed masses of plant materials, such as hay or manure piles. In haystacks, for example, high temperatures are likely to develop, even to the
point where the hay spontaneously ignites. This has been shown to be
the result of bacterial action; the rise in temperature is accompanied by
a loss in weight of the hay, and gaseous products and volatile acids are
formed (112,113,119,120).
Alteration of plant material by thermophilic
bacteria is sometimes used in the preparation of certain types of fodder
or manure (121-123).
In general, however, thermophilic bacteria are a nuisance rather than
a help in agricultural and industrial practice. Thermophilic sporeformers are among the principal causes of spoilage of canned foods,
since not only are their vegetative cells adapted to life at elevated
temperatures, but also their spores are unusually heat resistant, some
* The "thermophilic" strains of Chlorella pyrenoidosa which have recently been
reported (81) have a temperature maximum only slightly above 40°. The only
chlorophyte known which can grow at a temperature of 55° is Cyanidium
caldarium
(81a).