Sole Electron Source Research Articles

Chemolithoautotrophic growth on elemental sulfur (S°) and respiratory oxidation of S° byThiobacillus versutusand another sulfur-oxidizing bacterium

Thiobacillus versutus was shown to grow chemolithoautotrophically under microaerophilic conditions, with crystalline elemental sulfur (S°) and thiosulfate as sole electron source. The exponential growth rate on S° (µ = 0.106 h−1) measured in batch culture was similar to the reported maximum growth rate on thiosulfate in chemostat cultures. The rates of thiosulfate, S° and sulfite oxidation were measured respirometrically using an oxygen electrode. During growth under air on thiosulfate, as well as under low oxygen pressure on S° and thiosulfate, a relatively strong sulfuroxidizing activity (SOA) was measured. The induction of the SOA on cells growing with thiosulfate and the similar growth rates on S° and thiosulfate strongly suggest that S° could be an important intermediate during thiosulfate utilization.

A simple membrane-filter technique for the enumeration of S-reducing bacteria in soil and water samples

A new membrane-filter technique, suitable for field-surveys, was developed to quantify S-reducing bacteria in waters and soil or sediment samples. Samples, diluted if necessary; were passed through S-coated filters, previoulsy coated with a Fe(OH) 2 film. These filters were incubated in screw-cap test-tubes containing a selective medium, in which sodium acetate was the sole electron source. Blackening of the filter, resulting from iron monosulfide production was used as internal growth indicator, and the times necessary for total blackening of each filter to occur were correlated to the initial numbers of viable cells deposited on it.

Component A3 of the methylcoenzyme M methylreductase system of Methanobacterium thermoautotrophicum delta H: resolution into two components.

Component A3 of the methylcoenzyme M methylreductase system of Methanobacterium thermoautotrophicum (strain delta H) has been resolved into two fractions. One, named component A3a, was defined as the fraction required along with components A2 and C to produce methane from 2-(methylthio)ethanesulfonate when titanium(III) citrate was used as the sole source of electrons. The second one, named component A3b, was required when H2 and 7-mercapto-N-heptanoyl-O-phospho-L-threonine were provided as the dual source of electrons. Component A3a was a large iron-sulfur protein aggregate (Mr 500,000) and is most likely involved in providing electrons at a low potential for the reductive activation of component C.

Spin-fluctuation resonance in mixed-valence materials.

We analyze the neutron magnetic form factor of a lattice of fluctuating spins when the narrow band of resonance levels is partially occupied. The form factor is predominantly that of the conduction electrons at the Fermi level. This result shows that spin fluctuation is not the sole source of heavy electrons in a number of mixed-valence and heavy-electron systems, which have been shown experimentally to have f-electron form factors in the Fermi-liquid phase. A resolution of this dilemma is proposed and the proper place where the spin-fluctuation theory applies is identified.

Energy transduction efficiencies in nitrogenous oxide respirations of Azospirillum brasilense Sp7

For Azospirillum brasilense Sp7, the energy transformation efficiencies were measured in anaerobic respirations with either nitrate, nitrite or nitrous oxide as respiratory electron acceptors by determining the maximal molar growth yields and the H+-translocations using the oxidant pulse method. In continuous cultures grown with malate limiting, the maximal molar growth yields (Y s max -values) were essentially the same with O2 or N2O but were 1/3 and 2/3 lower with NO 2 - or NO 3 - , respectively, as respiratory electron acceptors. Both the maximal molar growth yields and the maintenance energy coefficients were surprisingly high when Azospirillum was grown with nitrite as the sole electron acceptor and source for N-assimilation. Growth under N2-fixing conditions drastically reduced the Y s max -values in the N2O and O2-respiring cells. In the H+-translocation measurements, the $$\vec H^ + $$ /oxidant ratios were 5.6 for O2→H2O, 2.5–2.8 for NO 3 - →NO 2 - , 2.2 for NO 2 - →N2O and 3.1 for N2O→N2 respirations when the cells were preincubated with valinomycin and K+. All the values were enhanced when the experiments were performed with valinomycin plus methyltriphenylphosphonium (=TPMP+) cation. The uncoupler carbonyl cyanide-m-chlorophenyl-hydrazone diminished the H+-excretion indicating that this translocation was due to vectorial flow across the membrane. In the absence of any ionophore, nitrate and nitrite respirations were accompanied by a H+-uptake $$(NO_3^ - \to N_2 = - 2.9 \vec H^ + /NO_3^ - and NO_2^ - \to N_2 = - 2.5 \vec H^ + /NO_2^ - )$$ . Any significant H+-translocation could not be detected in N2O- and O2-respirations under these conditions. It is concluded that nitrate reduction proceeds inside the cytoplasmic membrane, whereas nitrite is reduced extramembraneously. The data are not conclusive for the location of nitrous oxide reductase. The maximal molar growth yield determinations and the absence of any H+-uptake in untreated cells indicate a cytoplasmic orientation of the enzyme similar to the terminal cytochrome oxidase of respiration. The low H+-extrusion values for N2O-respiration compared to O2-respiration in cells treated with valinomycin plus TPMP+ are, however, not in accord with such an interpretation.

Activation of formylmethanofuran synthesis in cell extracts of Methanobacterium thermoautotrophicum.

In cell extracts of Methanobacterium thermoautotrophicum, formylmethanofuran (formyl-MFR) synthesis (an essential CO2 fixation reaction that is an early step in CO2 reduction to methane) is subject to a complex activation that involves a heterodisulfide of coenzyme M and N-(7-mercaptoheptanoyl)threonine O3-phosphate (CoM-S-S-HTP). In this paper we report that titanium(III) citrate, a low-potential reducing agent, stimulated CO2 reduction to methane and activated formyl-MFR synthesis in cell extracts. Titanium(III) citrate functioned as the sole source of electrons for formyl-MFR synthesis and enabled this reaction to occur independently of CoM-S-S-HTP. In addition, CoM-S-S-HTP was found to activate an unknown electron carrier that reduced metronidazole. The activation of formyl-MFR synthesis by CoM-S-S-HTP may involve the activation of a low-potential electron carrier.

Evidence that the heterodisulfide of coenzyme M and 7-mercaptoheptanoylthreonine phosphate is a product of the methylreductase reaction in Methanobacterium

When 7-mercaptoheptanoylthreonine phosphate (HS-HTP) was used as the sole source of electrons for reductive demethylation of 2-(methylthio)-ethanesulfonic acid (CH 3-S-CoM) by cell extracts of Methanobacterium thermoautotrophicum strain ΔH, the heterodisulfide of coenzyme M and HS-HTP (CoM-S-S-HTP) was quantitatively produced: HS-HTP + CH 3-S-CoM → CH 4 + CoM-S-S-HTP. CH 4 and CoM-S-S-HTP were produced stoichiometrically in a ratio of 1:1. Coenzyme M (HS-CoM) inhibited HS-HTP driven methanogenesis indicating that CH 3-S-CoM rather than HS-CoM was the substrate for CoM-S-S-HTP formation.

Bacterial Methanogenesis and Growth from CO 2 with Elemental Iron as the Sole Source of Electrons

Previous studies of anaerobic biocorrosion have suggested that microbial sulfur and phosphorus products as well as cathodic hydrogen consumption may accelerate anaerobic metal oxidation. Methanogenic bacteria, which normally use molecular hydrogen (H(2)) and carbon dioxide (CO(2)) to produce methane (CH(4)) and which are major inhabitants of most anaerobic ecosystems, use either pure elemental iron (Fe(0)) or iron in mild steel as a source of electrons in the reduction of CO(2) to CH(4). These bacteria use Fe(0) oxidation for energy generation and growth. The mechanism of Fe(0) oxidation is cathodic depolarization, in which electrons from Fe(0) and H(+) from water produce H(2), which is then released for use by the methanogens; thermodynamic calculations show that significant Fe(0) oxidation will not occur in the absence of H(2) consumption by the methanogens. The data suggest that methanogens can be significant contributors to the corrosion of iron-containing materials in anaerobic environments.

Growth of thermophilic, obligatorily chemolithoautotrophic hydrogen-oxidizing bacteria related toHydrogenobacterwith thiosulfate and elemental sulfur as electron and energy source

Strains related to Hydrogenobacter, a genus of thermophilic, obligatorily chemolithoautotrophic bacteria, were able to utilize elemental sulfur or thiosulfate, as well as molecular hydrogen, as sole electron and energy source. Extracellular elemental sulfur was produced as an intermediate during oxidation of thiosulfate. Growth with thiosulfate alone was strongly microaerophilic, whereas no hydrogenase activity was detected. Mixolithotrophic growth with both hydrogen and thiosulfate was faster than with hydrogen alone, and the cells harbored a hydrogenase activity comparable to that of cells grown under hydrogen without thiosulfate.

Growth of thermophilic, obligatorily chemolithoautotrophic hydrogen-oxidizing bacteria related to Hydrogenobacter with thiosulfate and elemental sulfur as electron and energy source

Strains related to Hydrogenobacter, a genus of thermophilic, obligatorily chemolithoautotrophic bacteria, were able to utilize elemental sulfur or thiosulfate, as well as molecular hydrogen, as sole electron and energy source. Extracellular elemental sulfur was produced as an intermediate during oxidation of thiosulfate. Growth with thiosulfate alone was strongly microaerophilic, whereas no hydrogenase activity was detected. Mixolithotrophic growth with both hydrogen and thiosulfate was faster than with hydrogen alone, and the cells harbored a hydrogenase activity comparable to that of cells grown under hydrogen without thiosulfate.

Cholesterol esters and steroidogenesis in pig corpora lutea

The corpus luteum of a number of species, including pig, contains quantities of cholesterol esters [ 1, 2, 31 which vary in concentration during the oestrus cycle [4] . Since an inverse relationship obtains between the amount of cholesterol esters present, and the progestational secretory activity [l] it was proposed that the sterol esters were stored precursors for ovarian steroidogenesis [4, 5, 61. That luteinizing hormone, which stimulates steroidogenesis, induces depletion of ovarian cholesterol esters [7, 81 is well established. The present study demonstrates that (i) cholesterol from cholesterol-fatty acids (FA) ester can be converted to pregnenolone and progesterone in luteal mitochondria and (ii) that the FA moiety of the sterol ester provides a potential source of electrons for the steroid hydroxylation reactions necessary for this conversion. The cholesterol side-chain cleavage (SCC) reaction is energy dependent when FA is the sole source of electrons.

The Enzymology of Nitrogen Fixation in Cell-free Extracts of Clostridium Pasteurianum

Abstract Extracts of Clostridium pasteurianum have been separated into five protein fractions, which are necessary for nitrogen fixation when pyruvate is used as the source of energy and electrons. Pyruvate oxidase is shown to be heat-stable and to have gel filtration properties corresponding to a molecular weight of 100,000 or greater. The function of ferredoxin as an electron carrier for nitrogen fixation is verified. In addition, it is shown here that reduced ferredoxin can act as the sole source of electrons for nitrogen fixation and for acetylene reduction. Fraction C1S1, which is necessary for both nitrogen fixation and acetylene reduction, has gel filtration properties corresponding to a molecular weight of 100,000 or greater. Its activity is stable at 0° but not at 60°, and is found in nitrogen-grown cells but not in ammonium sulfate-grown cells. Fraction IVn, which is necessary for nitrogen fixation but not for acetylene reduction, is of a size corresponding to a molecular weight of 40,000. Its activity is present only in cells grown on nitrogen gas, and this activity is stable at 0° as well as at 60°. Fraction IVs is necessary for both nitrogen fixation and acetylene reduction, and its size corresponds to a molecular weight of about 45,000. Its activity, which is found in cells grown on either nitrogen gas or ammonium sulfate, is stable at 60° but not at 0°. The properties of these fractions are compared with those of similar fractions previously described.