Mixotrophic growth of a thermoacidophilic iron-oxidizing, facultatively autotrophic bacterium is described. Rapid growth with sucrose, fructose, glucose and ribose required the concurrent oxidation of ferrous iron, which, it was concluded, provided most of the energy required for biosynthesis. Specific iron oxidation rate during growth and biomass production depended on the sugar supplied. About 20% of the cell carbon was obtained from CO-fixation during growth on glucose. The presence of ribulosebisphosphate carboxylase indicated this to be fixed by the Calvin cycle. The kinetics and inhibition of glucose transport indicated uptake by diffusion and by energy-dependent processes. Sensitivity to fluoride indicated the possible involvement of a phosphoenolpyruvate-phosphotransferase system. Radiorespirometry, using specifically labelled glucose molecules, demonstrated that glucose was oxidized by the oxidative pentose phosphate cycle with further oxidation of glyceraldehyde 3-phosphate by means of the tricarboxylic acid cycle. Dehydrogenases for glucose 6-phosphate and 6-phosphogluconate were present but 6-phosphogluconate dehydratase and 2-keto-3-deoxy-6-phosphogluconate aldolase were not detected in cell-free extracts, showing absence of the Entner-Doudoroff pathway.


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