Effect of Thiosulfate on the Photosynthetic Growth of Rhodopseudomonas palustris

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 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.

Phospholipids of the Thiobacilli

“…The presence of the methylated forms of PE in the thiobacilli and photosynthetic bacteria and the ability of certain members of both groups to utilize reduced sulfur compounds (17,19) supports the theory that these organisms are closely related. This theory is further supported by the recent finding that the growth of T. neapolitanus is stimulated by light (15).…”

Formic Hydrogenlyase and the Photoassimilation of Formate by a Strain of Rhodopseudomonas palustris

“…The photosynthetic organism was in part identified as a strain of R. palustris on the basis of its ability to grow autotrophically with thiosulfate on a medium containing yeast extract; this property was found to be characteristic of all strains of R. palustris studied by van Niel (42). Thiosulfate utilization by R. palustris has been reexamined recently by Rolls and Lindstrom (36,37). Our strain of R. palustris could not be grown strictly autotrophically on chemically defined media which supported heterotrophic growth on a wide variety of organic compounds.…”

Iron oxidation is regulated by the two-component system, RegSR, and plays a role in photolithoheterotrophic growth in Rhodopseudomonas palustris

“…However, it was unclear why pioABC is expressed under photoheterotrophic conditions, and why its expression increases when an oxidized carbon substrate is provided. R. palustris has been shown to oxidize thiosulfate or H2 during photoheterotrophic growth on an oxidized carbon substrate, particularly when these substrates are limiting (less than 40 mM total carbon) (29,31,43). This allows R. palustris access to an additional electron source to allow complete assimilation of oxidized carbon compounds (29,31,43).…”

“…R. palustris grows best as a photoheterotroph using energy generated by cyclic photophosphorylation and by metabolizing organic acids like malate or succinate and is known for its ability to fix nitrogen (27,28). R. palustris can also grow as a photoautotroph using Fe(II), hydrogen, or thiosulfate as an electron donor (21,(29)(30)(31). Iron oxidation in R. palustris TIE-1 requires the pioABC operon (20), which encodes PioA, a decaheme c-type cytochrome; PioB, an outer membrane porin; and PioC, a periplasmic high-potential iron protein (HiPIP) (33,34).…”