Thermoplasma acidophilum: Glucose Degradative Pathways and Respiratory Activities

Abstract

Soluble extracts of Thermoplasma acidophilum consumed O 2 when provided with anyof a variety of metabolic substrates. About 80 of the total cellular respiratory activity was in the soluble fraction, and about 20 in the particulate membrane fraction. Intermediates in the pentose phosphate pathway and Krebs Cycle were among the best substrates for respiration in vitro . Intermediates in the Embden-Meyerhoff glycolytic sequence were also effective, as were several 1- and 2-carbon compounds such as acetaldehyde and formate. When radioactive 14 C -glucose was given to living cultures the excretory products CO 2 and acetic acid became radioactive. The molar ratio of CO 2 to acetic acid was variable, but generally about 3. Intracellular metabolites that became 14 C-labeled were those expected from the pentose phosphate pathway, glycolysis, and the Krebs Cycle. The disaccharide maltose also became labeled. Although T. acidophilum should have the potential for anaerobic metabolism,experimentally it survived for only about 20 min without O 2 . Continuous aeration is apparently required for the regulation of intracellular pH.