| dc.description.abstract | A beginning was made in this country in the systematic study of spore‑forming bacteria capable of growing at 55°C. Ninety‑five odd isolates were obtained from sources such as soils, water from hot springs, air, dust, and a canned mango sample. The recent classification of spore‑forming bacteria put forward by Smith and his colleagues was made use of in the identification of these isolates. Of these, thirty‑six were identified as strains of B. subtilis, nine as strains of B. coagulans, five as strains of B. megaterium, four as strains of B. firmus, four as strains of B. sphaericus, three as strains of B. brevis, and one as a strain of B. stearothermophilus, while the rest remained unidentified.
The temperature characteristics of these isolates were investigated. The isolates were tested for growth at room temperature, 37°C and 55°C. About fifty per cent of the isolates could grow at incubation temperatures ranging from room temperature to 55°C., about twenty‑eight per cent were obligate thermophiles, about seventeen per cent could grow at 55° and 37°C but not at room temperature, and the remainder remained undetermined.
The probable origin of thermophilic bacilli is also given. This was deduced from several experiments carried out on this aspect of thermophily. The results of these experiments tend to confirm the belief that thermophiles are mutants of the common mesophilic forms. The mutagenic action of heat is indicated by the high frequency of occurrence of thermophilic forms from mesophilic populations and by the changes in the nature of the colonies at the different temperatures of incubation. A probable explanation for the ability of microorganisms to grow at elevated temperatures is also given.
An investigation of the amino acid composition of thermophilic bacilli and the corresponding mesophilic forms was undertaken with a view to see if there were any differences in the amino acid make‑up of the two forms. Several strains of B. subtilis grown at 55° and 37°C were analysed for their amino acids making use of chromatographic methods. No difference in the amino acid composition of the bacteria grown at these incubation temperatures was observed. The following amino acids were identified:
Alanine
Arginine
Aspartic acid
Cystine
Glutamic acid
Glycine
Histidine
Lysine
Methionine
Phenylalanine
Proline
Serine
Threonine
Tyrosine
It is suggested that an investigation of the free amino acids present in the bacilli grown at the two temperatures of incubation may reveal qualitative if not quantitative differences in the amino acid composition.
An attempt was made to assess the nutritional requirements of thermophiles. A preliminary screening revealed that thermophiles are definitely more exacting at the higher incubation temperatures. The isolates were tested for growth in a medium containing an inorganic source of nitrogen, minerals, and glucose as the source of carbon. None of the isolates tested could grow in this medium at 55°C although strains of B. subtilis which could grow at 37°C did grow in this medium at this temperature of incubation. In the next stage of the nutritional experiments biotin was added to the above inorganic nitrogen medium to see whether this could allow thermophiles to utilise inorganic nitrogen at 55°C. No growth was obtained with any of the isolates tested in this medium at the incubation temperature of 55°C. nor did it permit the growth of isolates which failed to grow at 37°C in the inorganic nitrogen medium alone.
Next we tried to determine the exact nutritional requirements of two strains of B. coagulans and a strain of B. brevis. A strain of B. coagulans (Bangl) showed a requirement for thiamine, cystine and histidine while the other B. coagulans strain seemed to require only methionine at 55°C. At 37°C no nutrilite seemed to be demanded by either of the strains. The results obtained with B. brevis were inconsistent and consequently are not presented. Our results indicate that this aspect of thermophily deserves further investigation. | |
