Biochemical Studies on an Acidophilic, Thermophilic Bacterium, Bacillus acidocaldarius: Isolation of Bacteria, Intracellular pH, and Stabilities of Biopolymers

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Abstract
Acidophilic, thermophilic bacteria were isolated from Japanese acidic hot springs. They were spore-forming rods, identified as Bacillus acidocaldarius. DNA extracted from these acidothermophiles showed no abnormality in chemical structure; it was instantly denatured and gradually decomposed giving rise to apurinic acid in a hot acid environment milder than the optimal conditions for the growth of the acido-thermophiles. Glyceraldehyde-3-phosphate dehydrogenase extracted from B. acidocaldarius was not active at pH 5 or less, and was resistant to heat at neutral but not acid pH. The intracellular pH was computed to be neutral by using dimethyl-2,4-oxazolidinedione. When uncouplers or inhibitors of respiration were added to the cells suspended in hot acid solution, the estimated pH was not changed and glyceraldehyde-3-phosphate dehydrogenase in the cells was not denatured. These results suggest that the cytoplasm of B. acidocaldarius is a hot neutral environment, and that a pH gradient across the cell envelope can be maintained even when oxidative phosphorylation or respiration is inhibited.