Mutational and physiological enhancement of photosynthetic energy conversion in Rhodopseudomonas capsulata.

Photosynthetic growth of Rhodopseudomonas capsulata, a nonsulfur purple bacterium, is severely inhibited by inorganic arsenate when this anion is present equimolar to orthophosphate in the culture medium. Studies on an arsenate-resistant mutant indicate that its resistance can be explained by a significantly increased photophosphorylation capacity of the energy-converting machinery, which can compensate for the decrease in adenosine triphosphate regeneration rate caused by esterification of arsenate in place of phosphate. Repeated subculture of the mutant in the presence of arsenate, under certain conditions, yields cell populations that have strikingly elevated contents of membrane-bound reaction-center bacteriochlorophyll, cytochromes, and photo-phosphorylation coupling factor. Membranes from such cells show unusually high photophosphorylation activity, and can be expected to provide a useful experimental material for more refined analysis of the mechanism of the energy-conversion process.