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Effect of Thiosulfate on the Photosynthetic Growth of Rhodopseudomonas palustris¹

^a Department of Microbiology, The Pennsylvania State University, University Park, Pennsylvania 16802

ABSTRACT

Cell yields of Rhodopseudomonas palustris grown photoheterotrophically in pyruvate-mineral salts medium were increased by the photooxidation of added thiosulfate. However, thiosulfate had no effect on cell yields of cultures grown aerobically in darkness, although thiosulfate was also oxidized. The presence of thiosulfate increased photosynthetic cell yields on a variety of other organic substrates. Growth of cells in thiosulfate-containing medium, or the addition of thiosulfate to cells grown in thiosulfate-free medium, induced the formation of a thiosulfate-oxidizing system which quantitatively photooxidized thiosulfate to sulfate. R. palustris grew photoautotrophically with thiosulfate as an oxidizable substrate. Large amounts of supplemental bicarbonate carbon were incorporated when cells were grown photosynthetically in pyruvate-thiosulfate medium. Cells harvested after photoautotrophic or photoheterotrophic growth in fumarate-thiosulfate medium fixed ¹⁴CO₂ at an 8- to 10-fold greater rate when provided with thiosulfate. The evolution of ¹⁴CO₂ from pyruvate-1-¹⁴C during photoassimilation by R. palustris was greatly suppressed by the presence of thiosulfate. The increase in photoheterotrophic cell yields of R. palustris caused by the oxidation of thiosulfate may result from assimilation of substrate carbon which is normally evolved as carbon dioxide.

² Present address: Department of Microbiology, Western Reserve University Medical School, Cleveland, Ohio.

¹ Part of the dissertation of James P. Rolls presented to the Graduate Faculty of the Pennsylvania State University in partial fulfillment of the requirement for the Ph.D. degree. Presented in part at the 65th Annual Meeting of the American Society for Microbiology, Atlantic City, N.J., 25–29 April 1965 (Bacteriol. Proc., p. 83–84) and in a preliminary abstract published in Federation Proc. 25:739 1966.