Fermentation and Anaerobic Respiration by Rhodospirillum rubrum and Rhodopseudomonas capsulata

Abstract

Rhodospirillum rubrum and Rhodopseudomonas capsulata were able to grow anaerobically in the dark either by a strict mixed-acid fermentation of sugars or, in the presence of an appropriate electron acceptor, by an energy-linked anaerobic respiration. Both species fermented fructose without the addition of accessory oxidants, but required the initial presence of bicarbonate before fermentative growth could begin. Major products of R. rubrum fermentation were succinate, acetate, propionate, formate, hydrogen, and carbon dioxide; R. capsulata produced major amounts of lactate, acetate, succinate, hydrogen, and carbon dioxide. R. rubrum and R. capsulata were also capable of growing strictly through anaerobic, respiratory mechanisms. Nonfermentable substrates, such as succinate, malate, or acetate, supported growth only in the presence of an electron acceptor such as dimethyl sulfoxide or trimethylamine oxide. Carbon dioxide and dimethyl sulfide were produced during growth of R. rubrum and R. capsulata on succinate plus dimethyl sulfoxide. Molar growth yields from cultures grown anaerobically in the dark on fructose plus dimethyl sulfoxide were 3.8 to 4.6 times higher than values obtained from growth on fructose alone and were 56 to 60% of the values obtained from aerobic, respiratory growth with fructose. Likewise, molar growth yields from anaerobic, respiratory growth conditions with succinate plus dimethyl sulfoxide were 51 to 54% of the values obtained from aerobic, respiratory growth with succinate. The data indicate that dimethyl sulfoxide or trimethylamine oxide as a terminal oxidant is approximately 33 to 41% as efficient as 02 in conserving energy through electron transport-linked respiration.

Biochemical genetics revisited: the use of mutants to study carbon and nitrogen metabolism in the photosynthetic bacteria

“…In these studies, no growth was observed in the absence of added electron acceptor. In contrast, Schultz and Weaver [100] found that, if yeast extract and NaHCO 3 were added to the medium, and if strict precautions were taken to remove 0 2, then Rb. capsulatus grew on fructose in the dark in the absence of DMSO, and also grew on the non-fer- Chromatium vinosum contains the/classical, LsS 8 form of Rubisco [108], although a fully active L s form can be obtained from the native form by dissociation [109].…”

“…sphaeroides in being able to carry out classical fermentative metabolism (although see [100]) by a mechanism involving pyruvate:formate lyase, which is inhibited by sodium hypophosphite [113]. Acetate, formate, H 2 and CO 2 appear to be the main fermentation products [114], although propionate, butyrate and succinate have also been detected [100,115]. There appears to be some interstrain variation, since strains S1 and Ha failed to produce acetate, and strain Ha failed to metabolize formate to H 2 and CO 2 [116].…”

Inability of men mutants of Escherichia coli to use trimethylamine-N-oxide as an electron acceptor

“…They further showed that the organism can fix nitrogen under these conditions [7]. Shultz and Weaver [8] surveyed a large number of photosynthetic bacteria for their ability to use TMAO as an electron acceptor and showed that this property is widespread among Rhodospirillaceae.…”

Anaerobic respiration in the Rhodospirillaceae: characterisation of pathways and evaluation of roles in redox balancing during photosynthesis

“…Only recently has the generality of anaerobic respiration in the Rhodospirillaceae become evident. The utilisation of nitrate, nitrous oxide, TMAO and DMSO as electron sinks for anaerobic respiratory pathways is now well-documented in a large number of strains [6,31,32]. Originally some of these reductive processes were not recognized as energy conserving and were attributed to fermentation reactions or to nitrogen-assimilation pathways.…”

“…The physiology and biochemistry of aerobic, chemoheterotrophic growth as well as the processes leading to photoheterotrophic growth have been studied in detail [2,3]. Photoautotrophic and chemoautotrophic growth with H 2 and CO 2 have also been characterised [4,5] together with some modes of fermentative growth [6]. The purpose of this article is to summarise and review recent findings concerning the ability of the Rhodospirillaceae to use a variety of acceptors in anaerobic electron transport reactions.…”