Fermentative metabolism of pyruvate by Rhodospirillum rubrum after anaerobic growth in darkness

Abstract

Rhodospirillum rubrum grew anaerobically in darkness and fermented sodium pyruvate by a pyruvate formate-lyase reaction. During 30 min of anaerobic dark or light incubation with sodium pyruvate, crude extracts from fermentatively grown cells produced about 6 yimol of acetylphosphate and formate per mg of protein in reactions performed at pH 8.3. Cell extracts also catalyzed the exchange of sodium [14C]formate into sodium pyruvate at an apparent pH optimum of 7.3 to 7.5, but only about 2.5 ,zmol of acetylphosphate was produced at this lower pH value. R. rubrum may also form pyruvate:ferredoxin oxidoreductase activity, as evidenced by low bicarbonate exchange activity. However, its participation in pyruvate metabolism in anaerobic dark-grown cells was not understood. During anaerobic, dark growth with pyruvate, formate was an intermediate in H2 and C02 gas evolution. In contrast with H2 production by a light-dependent H2-nitrogenase system in photosynthetically grown cells, H2 formation in fermenting R. rubrum occurred through a carbon monoxidesensitive formic hydrogenlyase reaction not influenced by light.

Regulation of anaerobic carbon monoxide oxidation activity in Rhodocyclus gelatinosus

“…In earlier studies, Rhodospirillum rubrum, also an anoxygenic phototrophic bacterium, grew in the dark and metabolized pyruvate by a substrate-inducible fermentation system [14]. When fermenting ceils were exposed to light, they continued to grow fermentatively, and only differentiated for light growth after the keto acid was used up [11].…”

Metabolism of carbon monoxide by Rhodopseudomonas gelatinosa: cell growth and properties of the oxidation system

“…Unless stated otherwise, R. gelatinosa was grown in a liquid mineral medium (37) supplemented with 0.1% (wt/vol) Trypticase (BBL Microbiology Systems, Cockeysville, Md.). The CO medium was prepared under strictly anaerobic conditions essentially by methods described elsewhere (11,36,37). The medium did not contain resazurine as a redox indicator dye, and the cysteine-sulfide reducing agent was omitted from medium used for aerobic growth.…”

Chemotrophic growth of heliobacteria in darkness

“…Anaerobic chemotrophic growth of phototrophic bacteria was first discovered in Rhodospirillum rubrum and several other purple nonsulfur bacteria, where, like in heliobacteria, pyruvate served as energy source [16]. The mechanism of energy conservation in dark-grown R. rubrum was subsequently shown to be pyruvate cleavage by pyruvate-formate lyase, leading to the production of formate, CO 2, H 2, and acetate [17]. Glucose and fructose also support anaerobic dark growth of various purple non-sulfur bacteria, but in most cases this requires an electron acceptor such as TMAO or DMSO (reviewed in [1]).…”