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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.

reported that Rhodopseudomonas palustris grows photoautotrophically with thiosulfate as an oxidizable substrate. J. P. Rolls and E. S. Lindstrom (J. Bacteriol., in press) found that cell suspensions of R. palustris grown photosynthetically on organic substrates in thiosulfate-free media did not utilize thiosulfate immediately, as did cells grown either photoautotrophically or photoheterotrophically in thiosulfate-containing media. This thiosulfate-oxidizing system could be induced in cells grown in thiosulfate-free media if the cells were incubated for 8 hr under

The carbon skeleton of glucose is extensively randomized during conversion to cell wall glucosamine by Escherichia coli K-12. Exogenous glucosamine- 1 - 14 C is selectively oxidized, and isotope incorporation into cellular glucosamine is greatly diluted during assimilation. A mutant unable to grow with N -acetylglucosamine as a carbon and energy source was isolated from E. coli K-12. This mutant was found to be defective in glucosamine-6-phosphate deaminase. Glucosamine- 1 - 14 C and N -acetylglucosamine- 1 - 14 C were assimilated during the growth of mutant cultures without degradation or carbon randomization. Assimilated isotopic carbon resided entirely in cell wall glucosamine and muramic acid. Some isotope dilution occurred from biosynthesis, but at high concentrations (0.2 m m ) of added N -acetylglucosamine nearly all cellular amino sugar was derived from the exogenous source. Growth of the mutant was inhibited with 1 m m N -acetylglucosamine.

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