Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Dark fermentation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

7 recordsLinked to original sources
PubMed2026

Exploring biohydrogen producing potential of Arctic ice and water through metagenomics and dark fermentation kinetics.

Cryospheric ecosystems in the high Arctic harbor largely unexplored microbiomes with significant biotechnological potential. The present study evaluates the biohydrogen production capabilities of the indigenous microbiome of Ny-Ålesund, Svalbard, using glacial ice and surface water samples. Dark fermentation batch assays were performed at 4 °C and 20 °C with 2-bromoethanesulfonate (BES), a methanogenic inhibitor, to track the succession of metabolic and taxonomic diversity. Metagenomic and functional analyses revealed that under 20 °C and BES conditions, psychrotolerant microbial communities maximize biohydrogen production to 85% of the total biogas produced, with an acetate-dominant fermentation pathway, as inferred from volatile fatty acid (VFA) analysis. This evolves into a highly coordinated system utilizing a coupled Rnf-nitrogenase route alongside Formate Hydrogenlyase and [FeFe]-hydrogenase pathways. Kinetic modelling using the Modified Gompertz equation, along with Q10 temperature-sensitivity indices, demonstrated a very high latent catalytic potential in these cold-adapted microbiomes. This study indicates that Arctic microbiomes are highly elastic thermodynamically and could serve as highly efficient, manipulatable biocatalysts for the environmental recovery of bioenergy through engineered low-temperature systems.

Fermentation↗
PubMed1976

Pyruvate fermentation in Rhodospirillum rubrum and after transfer from aerobic to anaerobic conditions in the dark.

The fermentative metabolism of Rhodospirillum rubrum (strain Ha, F1, S1) was studied after transfering the cells from aerobic to anaerobic dark culture conditions. Pyruvate was metabolized mainly to acetate and formate, and to a lesser extent to CO2 and priopionate, by all strains. Therefore, pyruvate formate lyase would appear to be the characteristic key enzyme of the dark anaerobic fermentation metabolism in R. rubrum. Strain F1 and S1 metabolized the formate further to H2 and CO2. It is concluded that this cleavage was catalysed by a formate hydrogen lyase system. Strain Ha was unable to metabolize formate. The cleavage of formate and the synthesis of poly-beta-hydroxy-butyric acid were increased by a low pH value (approximately 6.5). Fermentation equations and schemes of the pyruvate metabolism are discussed.

Acetates↗
PubMed1977

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

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 pyrivate, crude extracts from fermentatively grown cells produced about 6 micronmol 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 micronmol 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 CO2 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 monoxide-sensitive formic hydrogenlyase reaction not influenced by light.

Aldehyde Oxidoreductases↗
PubMed1978

Pyruvate fermentation in light-grown cells of Rhodospirillum rubrum during adaptation to anaerobic dark conditions.

Pyruvate fermentation in Rhodospirillum rubrum (strains F1, S1, and Ha) was investigated using cells precultured on different substrates anaerobically in the light and than transferred to anaerobic dark conditions. Pyruvate formate lyase was always the key enzyme in pyruvate fermentation but its activity was lower than in cells which have been precultured aerobically in darkness. The preculture substrate also had a clear influence on the pyruvate formate lyase activity. Strains F1 and S1 metabolized the produced formate further to H2 and CO2. A slight production of CO2 from pyruvate, without additional H2-production, could also be detected. It was concluded from this that under anaerobic dark conditions a pyruvate dehydrogenase was also functioning. On inhibition of pyruvate formate lyase the main part of pyruvate breakdown was taken over by pyruvate dehydrogenase. When enzyme synthesis was inhibited by chloramphenicol, propionate production in contrast to formate production was not affected. Protein synthesis was not significant during anaerobic dark culture. Bacteriochlorophyll, however, showed, after a lag phase, a clear rise.

Adaptation, Physiological↗
PubMed1976

[Fermentation of pyruvate by 7 species of phototrophic purple bacteria].

The dark, anaerobic fermentation of pyruvate under growth conditions was examined with the following species of phototrophic purple bacteria: Rhodospirillum rubrum strains Ha and S1, Rhodopseudomonas gelatinosa strain 2150, Rhodopseudomonas acidophila strain 7050, Rhodopseudomonas palustris strain ATCC 17001, Rhodopseudomonas capsulata strains Kb1 and 6950, Rhodopseudomonas sphaeroides strain ATCC 17023, and Chromatium vinosum strain D. Fermentation balances were established for all experiments. Under fermentative conditions cell protein and dry weight increased only slightly, if at all. The species differed considerably in their fermentative activity; R. rubrum and R. gelatinosa exhibited the highest rates (2-8 mumoles pyruvate/mg protein-h). R. acidophila and R. capsulata showed an intermediate fermentation rate (0.4--2.0 mumoles pyruvate/mg protein-h), while the other strains tested fermented at quite low rates (0.2-0.4 mumoles pyruvate/mg protein-h). The extremes of fermentation times were from 30-380 hours. Based on the products of fermentation which were formed in addition to acetate, formate, and CO2, the species can be grouped as follows: a) R. rubrum, R. gelatinosa, and R. sphaeroides additionally form propionate. b) R. gelatinosa, R. palustris, R. capsulata, R. sphaeroides, and C. vinosum additionally form lactate. R. palustris also produces butyrate. c) R. acidophila and R. capsulata additionally form much 2,3-butanediol, acetoin, and diacetyl. Small amounts of acetoin were formed by the rest of the strains. A comparison of the fermentation of pyruvate by normal and starved cells (4 days in the light without a carbon source) of R. rubrum and R. gelatinosa shows that the latter ferment more slowly and produce less acetate and formate, but more propionate or lactate. The fermentation of pyruvate by R. rubrum was also studied in cultures in which the pH fell (7.2--6.6). Compared with the fermentation at neutral pH (7.3, 7.4), the following differences were found: a slower fermentation rate, an increased production of dry weight, an increased formation of propionate, but a reduced formation of acetate and a very low production of formate.

Acetates↗
PubMed1975

Lactate dehydrogenases in cyanobacteria.

NAD-linked lactate dehydrogenases specific for the D- and L-lactate have been demonstrated in a number of strains of unicellular cyanobacteria. The D-lactate dehydrogenase of one strain (Synechococcus 6716) was partially purified and its properties were studied. The enzyme has a molecular weight of ca. 115000-120000, is highly specific, autooxidizable, and susceptible to inhibition by iodoacetamide, oxamate and ATP. The possible physiological functions of the enzyme in the metabolism of the organism were investigated. D-lactate carbon was incorporated in cell material during photosynthetic growth with CO2, but lactate was not used as sole source for carbon for photosynthetic or chemosynthetic development. D-lactate and pyruvate were oxidized aerobically in the dark by resting cell suspensions with the assimilation mainly of the C2 and the C3 carbon atoms. In the oxidation of lactate, acetate was excreted into the medium. No fermentation of glucose was found, but a small amount of D-lactate was detected as a product of endogenous dark metabolism of the cell. All enzymes required for the production of lactate from glucose and from glycogen were found in exponentially growing cells, but the activity of some key enzymes was low or undetectable in old cultures.

Acetates↗
PubMed1978

Reduction of nicotinamide adenine dinucleotide by pyruvate:lipoate oxidoreductase in anaerobic, dark-grown Rhodospirillum rubrum mutant C.

Cell extracts from fermentatively grown Rhodospirillum rubrum reduced about 80 nmol of nicotinamide adenine dinucleotide (NAD) per mg of protein per min under anaerobic conditions with sodium pyruvate. The reaction was specific for pyruvate and NAD; NAD phosphate was not reduced. Results indicated that pyruvate-linked NAD reduction occurred via pyruvate:lipoate oxidoreductase. The reaction required catalytic amounts of both coenzyme A and thiamine pyrophosphate. Addition of sodium arsenite inhibited enzyme activity by 90%. Pyruvate:lipoate oxidoreductase was the only system detected in anaerobic, dark-grown R. rubrum cell extracts which operated to produce reduced NAD. The low activity of the enzyme system suggested that it was not quantitatively important in ATP formation.

Anaerobiosis↗