Humic Acid Reduction by Propionibacterium freudenreichii and Other Fermenting Bacteria

ABSTRACT Iron-reducing bacteria have been reported to reduce humic acids and low-molecular-weight quinones with electrons from acetate or hydrogen oxidation. Due to the rapid chemical reaction of amorphous ferric iron with the reduced reaction products, humic acids and low-molecular-weight redox mediators may play an important role in biological iron reduction. Since many anaerobic bacteria that are not able to reduce amorphous ferric iron directly are known to transfer electrons to other external acceptors, such as ferricyanide, 2,6-anthraquinone disulfonate (AQDS), or molecular oxygen, we tested several physiologically different species of fermenting bacteria to determine their abilities to reduce humic acids.Propionibacterium freudenreichii, Lactococcus lactis, and Enterococcus cecorum all shifted their fermentation patterns towards more oxidized products when humic acids were present; P. freudenreichii even oxidized propionate to acetate under these conditions. When amorphous ferric iron was added to reoxidize the electron acceptor, humic acids were found to be equally effective when they were added in substoichiometric amounts. These findings indicate that in addition to iron-reducing bacteria, fermenting bacteria are also capable of channeling electrons from anaerobic oxidations via humic acids towards iron reduction. This information needs to be considered in future studies of electron flow in soils and sediments.

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The Behavior of Low Molecular Weight Organic Carbon-14 Containing Compounds in Contaminated Groundwater During Denitrification and Iron-Reduction

Geomicrobiology Journal ◽

10.1080/01490451.2020.1728442 ◽

2020 ◽

Vol 37 (5) ◽

pp. 486-495

Author(s):

Aislinn A. Boylan ◽

Douglas I. Stewart ◽

James T. Graham ◽

Ian T. Burke

Keyword(s):

Molecular Weight ◽

Organic Carbon ◽

Iron Reduction ◽

Contaminated Groundwater ◽

Low Molecular Weight ◽

Carbon 14

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STUDIES ON THE ISOLATION AND NATURE OF THE 'TERREGENS FACTOR'

Canadian Journal of Biochemistry and Physiology ◽

10.1139/y54-043 ◽

1954 ◽

Vol 32 (1) ◽

pp. 400-406 ◽

Cited By ~ 10

Author(s):

M. O. Burton ◽

F. J. Sowden ◽

A. G. Lochhead

Keyword(s):

Amino Acids ◽

Molecular Weight ◽

Ferric Iron ◽

Test Organism ◽

The Other ◽

Inorganic Salts ◽

Low Molecular Weight ◽

Straight Chain ◽

Heat Stable ◽

Growth Promoting

A procedure is described for the production and concentration of the 'terregens factor' (TF), a bacterial growth promoting substance synthesized by Arthrobacter pascens and essential for the growth of Arthrobacter terregens. From culture filtrates of A. pascens cultivated in a medium of inorganic salts and sucrose, concentrates of TF may be obtained that are active at 0.001 μgm. Per ml., heat stable and contain about 12.7% nitrogen. Acid hydrolysis yielded a number of amino acids, including glutamic acid, glycine, α–alanine, valine, leucine, proline, lysine, and arginine, as well as some unidentified compounds; however, TF does not appear to be a low molecular weight straight chain peptide.Although TF contains no iron, it combines readily with ferrous or ferric iron to form reddish-brown complexes with this metal. Activity for A. terregens is shown by certain iron containing complexes as hemin, coprogen, and ferrichrome. On the other hand none is shown by cytochrome or pulcherrimin; however, aspergillic acid, structurally related to the latter, possesses some growth promoting activity for the test organism.

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Can Primary Ferroan Dolomite and Ankerite Be Precipitated? Its Implications for Formation of Submarine Methane-Derived Authigenic Carbonate (MDAC) Chimney

Minerals ◽

10.3390/min9070413 ◽

2019 ◽

Vol 9 (7) ◽

pp. 413 ◽

Cited By ~ 2

Author(s):

Fan Xu ◽

Xuelian You ◽

Qing Li ◽

Yi Liu

Keyword(s):

Iron Reduction ◽

Extracellular Polymeric Substances ◽

Microbial Culture ◽

Reduction Zone ◽

Secondary Products ◽

Iron Reducing Bacteria ◽

Sulfate Reducing ◽

Dolomite Problem ◽

Reducing Bacteria ◽

Ferroan Dolomite

Microbes can mediate the precipitation of primary dolomite under surface conditions. Meanwhile, primary dolomite mediated by microbes often contains more Fe2+ than standard dolomite in modern microbial culture experiments. Ferroan dolomite and ankerite have been regarded as secondary products. This paper reviews the process and possible mechanisms of microbial mediated precipitation of primary ferroan dolomite and/or ankerite. In the microbial geochemical Fe cycle, many dissimilatory iron-reducing bacteria (DIRB), sulfate-reducing bacteria (SRB), and methanogens can reduce Fe3+ to Fe2+, while SRB and methanogens can also promote the precipitation of primary dolomite. There are an oxygen respiration zone (ORZ), an iron reduction zone (IRZ), a sulfate reduction zone (SRZ), and a methanogenesis zone (MZ) from top to bottom in the muddy sediment diagenesis zone. DIRB in IRZ provide the lower section with Fe2+, which composes many enzymes and proteins to participate in metabolic processes of SRB and methanogens. Lastly, heterogeneous nucleation of ferroan dolomite on extracellular polymeric substances (EPS) and cell surfaces is mediated by SRB and methanogens. Exploring the origin of microbial ferroan dolomite may help to solve the “dolomite problem”.

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Effect of Sub-Stoichiometric Fe(III) Amounts on LCFA Degradation by Methanogenic Communities

Microorganisms ◽

10.3390/microorganisms8091375 ◽

2020 ◽

Vol 8 (9) ◽

pp. 1375

Author(s):

Ana J. Cavaleiro ◽

Ana P. Guedes ◽

Sérgio A. Silva ◽

Ana L. Arantes ◽

João C. Sequeira ◽

...

Keyword(s):

Iron Reduction ◽

Anaerobic Bacteria ◽

Granular Sludge ◽

Microbial Interactions ◽

Methanogenic Activity ◽

Iron Reducing Bacteria ◽

Hydrogenotrophic Methanogenesis ◽

Degrading Bacteria ◽

Acetoclastic Methanogenesis ◽

Reducing Bacteria

Long-chain fatty acids (LCFA) are common contaminants in municipal and industrial wastewater that can be converted anaerobically to methane. A low hydrogen partial pressure is required for LCFA degradation by anaerobic bacteria, requiring the establishment of syntrophic relationships with hydrogenotrophic methanogens. However, high LCFA loads can inhibit methanogens, hindering biodegradation. Because it has been suggested that anaerobic degradation of these compounds may be enhanced by the presence of alternative electron acceptors, such as iron, we investigated the effect of sub-stoichiometric amounts of Fe(III) on oleate (C18:1 LCFA) degradation by suspended and granular methanogenic sludge. Fe(III) accelerated oleate biodegradation and hydrogenotrophic methanogenesis in the assays with suspended sludge, with H2-consuming methanogens coexisting with iron-reducing bacteria. On the other hand, acetoclastic methanogenesis was delayed by Fe(III). These effects were less evident with granular sludge, possibly due to its higher initial methanogenic activity relative to suspended sludge. Enrichments with close-to-stoichiometric amounts of Fe(III) resulted in a microbial community mainly composed of Geobacter, Syntrophomonas, and Methanobacterium genera, with relative abundances of 83–89%, 3–6%, and 0.2–10%, respectively. In these enrichments, oleate was biodegraded to acetate and coupled to iron-reduction and methane production, revealing novel microbial interactions between syntrophic LCFA-degrading bacteria, iron-reducing bacteria, and methanogens.

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Ferric Iron Reduction in Extreme Acidophiles

Frontiers in Microbiology ◽

10.3389/fmicb.2021.818414 ◽

2022 ◽

Vol 12 ◽

Author(s):

Luise Malik ◽

Sabrina Hedrich

Keyword(s):

Iron Reduction ◽

Ferric Iron ◽

Hydrogen Oxidation ◽

Iron Oxidation ◽

Minor Role ◽

Microbial Conversion ◽

Dissimilatory Iron Reduction ◽

Alternative Scenarios ◽

A Minor ◽

Life On Earth

Biochemical processes are a key element of natural cycles occurring in the environment and enabling life on earth. With regard to microbially catalyzed iron transformation, research predominantly has focused on iron oxidation in acidophiles, whereas iron reduction played a minor role. Microbial conversion of ferric to ferrous iron has however become more relevant in recent years. While there are several reviews on neutrophilic iron reducers, this article summarizes the research on extreme acidophilic iron reducers. After the first reports of dissimilatory iron reduction by acidophilic, chemolithoautotrophic Acidithiobacillus strains and heterotrophic Acidiphilium species, many other prokaryotes were shown to reduce iron as part of their metabolism. Still, little is known about the exact mechanisms of iron reduction in extreme acidophiles. Initially, hypotheses and postulations for the occurring mechanisms relied on observations of growth behavior or predictions based on the genome. By comparing genomes of well-studied neutrophilic with acidophilic iron reducers (e.g., Ferroglobus placidus and Sulfolobus spp.), it became clear that the electron transport for iron reduction proceeds differently in acidophiles. Moreover, transcriptomic investigations indicated an enzymatically-mediated process in Acidithiobacillus ferrooxidans using respiratory chain components of the iron oxidation in reverse. Depending on the strain of At. ferrooxidans, further mechanisms were postulated, e.g., indirect iron reduction by hydrogen sulfide, which may form by disproportionation of elemental sulfur. Alternative scenarios include Hip, a high potential iron-sulfur protein, and further cytochromes. Apart from the anaerobic iron reduction mechanisms, sulfur-oxidizing acidithiobacilli have been shown to mediate iron reduction at low pH (< 1.3) under aerobic conditions. This presumably non-enzymatic process may be attributed to intermediates formed during sulfur/tetrathionate and/or hydrogen oxidation and has already been successfully applied for the reductive bioleaching of laterites. The aim of this review is to provide an up-to-date overview on ferric iron reduction by acidophiles. The importance of this process in anaerobic habitats will be demonstrated as well as its potential for application.

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Dithionite Reduction in the Presence of a Tetrapyrrole-containing Fraction From the Desulfoviridin of Desulfovihrio gigas

Australian Journal of Biological Sciences ◽

10.1071/bi9770021 ◽

1977 ◽

Vol 30 (2) ◽

pp. 21 ◽

Cited By ~ 3

Author(s):

GW Skyring ◽

HE Jones

Keyword(s):

Molecular Weight ◽

Growth Medium ◽

Sodium Dithionite ◽

Low Molecular Weight ◽

Sulphate Reducing Bacteria ◽

Reducing Bacteria ◽

Molecular Weight Fractions

Low-molecular-weight fractions obtained from the desulfoviridin of D. gigas and from the growth medium of Desul/ovibrio sp. 10455 promoted the reduction of sodium dithionite to sulphide in the presence of reduced methylviologen. These fractions contained a tetrapyrrole of the isobacteriochI orin type which was not complexed with iron, nor was it complexed with protein. The observations are discussed in relation to the function of sulphite reductases in the sulphate-reducing bacteria.

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