Abstract
The bioenergetics of two extreme halophiles, Halobacterium halobium and Halobacterium marismortui, have been investigated by respiratory studies and in vivo nuclear magnetic resonance (NMR) spectroscopy. The phosphorus resonances of both species were very broad under anaerobic conditions, but sharpened somewhat on initiation of respiration and considerably upon cooling; changes attributable in part to slow chemical exchange processes. Transmembrane pH gradients (ΔpH) of H. marismortui were somewhat lower than those of H. halobium. Uncoupling agents caused ATP to disappear and inhibited respiration in both species, but dissipated ΔpH at best only partially. Uptake of Mn 2+ by H. halobium was unaffected by the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), whereas H. marismortui appeared not to transport the ion, even in the absence of uncoupler. FCCP caused a slow efflux of K + from H. halobium, but no K + was lost from H. marismortui. These findings are discussed with particular reference to the intracellular environments of the two organisms.
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