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 14C02 at an 8to 10-fold greater rate when provided with thiosulfate. The evolution of '4CO2 from pyruvate-1-'4C 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. Photosynthetic bacteria belonging to the Chlorobacteriaceae and the Thiorhodaceae, as well as Rhodomicrobium vanniellii (13), can grow photoautotrophically while oxidizing reduced inorganic sulfur compounds. In contrast, the Athiorhodaceae exhibit a photoheterotrophic metabolism at the expense of a variety of organic compounds. Van Niel (12) reported that Rhodopseudomonas palustris, a member of the Athiorhodaceae, was unique among the rhodopseudomonads in its ability to oxidize thiosulfate during photoautotrophic growth on bicarbonate. The present study was undertaken to determine the conditions under which thiosulfate is metabolized by R. palustris and the physiological consequence of thiosulfate oxidation on heterotrophic growth.
Rhodanese activity was demonstrated in extracts from all three taxonomic fami-L: lies of photosynthetic bacteria, and this activity appeared to be uncorrelated witki-. . thiosulfate metabolism.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.