Acetate Threshold Concentrations Suggest Varying Energy Requirements during Anaerobic Respiration by Anaeromyxobacter dehalogenans (original) (raw)
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Characterization of Fe(III) Reduction by Chlororespiring Anaeromxyobacter dehalogenans
Applied and Environmental Microbiology, 2003
Anaeromyxobacter dehalogenans strain 2CP-C has been shown to grow by coupling the oxidation of acetate to the reduction of ortho-substituted halophenols, oxygen, nitrate, nitrite, or fumarate. In this study, strain 2CP-C was also found to grow by coupling Fe(III) reduction to the oxidation of acetate, making it one of the few isolates capable of growth by both metal reduction and chlororespiration. Doubling times for growth of 9.2 and 10.2 h were determined for Fe(III) and 2-chlorophenol reduction, respectively. These were determined by using the rate of [14C]acetate uptake into biomass. Fe(III) compounds used by strain 2CP-C include ferric citrate, ferric pyrophosphate, and amorphous ferric oxyhydroxide. The addition of the humic acid analog anthraquinone 2,6-disulfonate (AQDS) increased the reduction rate of amorphous ferric iron oxide, suggesting AQDS was used as an electron shuttle by strain 2CP-C. The addition of chloramphenicol to fumarate-grown cells did not inhibit Fe(III) r...
Reductive dechlorination in the energy metabolism of anaerobic bacteria
FEMS Microbiology Reviews, 1998
Within the last few decades, several anaerobic bacteria have been isolated which are able to reductively dechlorinate chlorinated aliphatic and aromatic compounds at catabolic rates. For some of these bacteria, it has been shown that the reductive dechlorination is coupled to energy conservation, a process designated as`dehalorespiration'. Somewhat simple respiratory chains seem to be involved that utilize the free energy that could be gained from the exergonic dechlorination reaction quite inefficiently. With one exception, all reductive dehalogenases isolated to date contain a corrinoid and iron^sulfur clusters as cofactors. During the course of the catalytic reaction cycle, the cobalt of the corrinoid is subjected to a change in its redox state. Hence, reductive dechlorination represents a new type of biochemical reaction. z
FEMS Microbiology Ecology, 2009
In order to assess the importance of nitrate-dependent Fe(II) oxidation and its impact on the growth physiology of dominant Fe oxidizers, we counted these bacteria in freshwater lake sediments and studied their growth physiology. Most probable number counts of nitrate-reducing Fe(II)-oxidizing bacteria in the sediment of Lake Constance, a freshwater lake in Southern Germany, yielded about 10 5 cells mL À1 of the total heterotrophic nitrate-reducing bacteria, with about 1% (10 3 cells mL À1 ) of nitrate-reducing Fe(II) oxidizers. We investigated the growth physiology of Acidovorax sp. strain BoFeN1, a dominant nitrate-reducing mixotrophic Fe(II) oxidizer isolated from this sediment. Strain BoFeN1 uses several organic compounds (but no sugars) as substrates for nitrate reduction. It also reduces nitrite, dinitrogen monoxide, and O 2 , but cannot reduce Fe(III). Growth experiments with cultures amended either with acetate plus Fe(II) or with acetate alone demonstrated that the simultaneous oxidation of Fe(II) and acetate enhanced growth yields with acetate alone (12.5 g dry mass mol À1 acetate) by about 1.4 g dry mass mol À1 Fe(II). Also, pure cultures of Pseudomonas stutzeri and Paracoccus denitrificans strains can oxidize Fe(II) with nitrate, whereas Pseudomonas fluorescens and Thiobacillus denitrificans strains did not. Our study demonstrates that nitrate-dependent Fe(II) oxidation contributes to the energy metabolism of these bacteria, and that nitrate-dependent Fe(II) oxidation can essentially contribute to anaerobic iron cycling.
Thermodynamic Controls on the Kinetics of Microbial Low-pH Fe(II) Oxidation
Environmental Science & Technology, 2014
Acid mine drainage (AMD) is a major worldwide environmental threat to surface and groundwater quality. Microbial low-pH Fe(II) oxidation could be exploited for cost-effective AMD treatment; however, its use is limited because of uncertainties associated with its rate and ability to remove Fe from solution. We developed a thermodynamic-based framework to evaluate the kinetics of low-pH Fe(II) oxidation. We measured the kinetics of low-pH Fe(II) oxidation at five sites in the Appalachian Coal Basin in the US and three sites in the Iberian Pyrite Belt in Spain and found that the fastest rates of Fe(II) oxidation occurred at the sites with the lowest pH values. Thermodynamic calculations showed that the Gibbs free energy of Fe(II) oxidation (ΔG oxidation) was also most negative at the sites with the lowest pH values. We then conducted two series of microbial Fe(II) oxidation experiments in laboratory-scale chemostatic bioreactors operated through a series of pH values (2.1−4.2) and found the same relationships between Fe(II) oxidation kinetics, ΔG oxidation , and pH. Conditions that favored the fastest rates of Fe(II) oxidation coincided with higher Fe(III) solubility. The solubility of Fe(III) minerals, thus plays an important role on Fe(II) oxidation kinetics. Methods to incorporate microbial low-pH Fe(II) oxidation into active and passive AMD treatment systems are discussed in the context of these findings. This study presents a simplified model that describes the relationship between free energy and microbial kinetics and should be broadly applicable to many biogeochemical systems.
Acetate Oxidation Coupled to Fe(III) Reduction in Hyperthermophilic Microorganisms
Applied and Environmental Microbiology, 2001
No hyperthermophilic microorganisms have previously been shown to anaerobically oxidize acetate, the key extracellular intermediate in the anaerobic oxidation of organic matter. Here we report that two hyperthermophiles, Ferroglobus placidus and "Geoglobus ahangari," grow at 85°C by oxidizing acetate to carbon dioxide, with Fe(III) serving as the electron acceptor. These results demonstrate that acetate could potentially be metabolized within the hot microbial ecosystems in which hyperthermophiles predominate, rather than diffusing to cooler environments prior to degradation as has been previously proposed.
ATP requirements for growth and maintenance of iron-oxidizing bacteria
Biochemical Engineering Journal, 2004
A simple metabolic model of ferrous oxidizing bacteria based on biochemically structured balances of ATP and NAD(P)H is proposed in order to calculate maximum yield and maintenance on ATP. Similar values of growth yield and maintenance were obtained using data of ferrous iron and/or oxygen consumption in Acidithiobacillus ferrooxidans cultures on iron under different conditions. When pyrite was the sole energy source, growth yield was higher suggesting cells could obtain energy through the sulfur compounds oxidation. Values of growth yields for Leptospirillum ferrooxidans cultures on iron were a bit lower than those obtained for A. ferrooxidans although within the experimental errors. The maintenance coefficients on ATP for both bacteria were similar and comparable to those observed in heterotrophic microorganisms. This fact is really surprising taking in account the high proton gradient that this kind of microorganisms should maintain.
Applied and …, 2007
We analyzed the carbon fluxes in the central metabolism of Geobacter metallireducens strain GS-15 using 13 C isotopomer modeling. Acetate labeled in the first or second position was the sole carbon source, and Fenitrilotriacetic acid was the sole terminal electron acceptor. The measured labeled acetate uptake rate was 21 mmol/g (dry weight)/h in the exponential growth phase. The resulting isotope labeling pattern of amino acids allowed an accurate determination of the in vivo global metabolic reaction rates (fluxes) through the central metabolic pathways using a computational isotopomer model. The tracer experiments showed that G. metallireducens contained complete biosynthesis pathways for essential metabolism, and this strain might also have an unusual isoleucine biosynthesis route (using acetyl coenzyme A and pyruvate as the precursors). The model indicated that over 90% of the acetate was completely oxidized to CO 2 via a complete tricarboxylic acid cycle while reducing iron. Pyruvate carboxylase and phosphoenolpyruvate (PEP) carboxykinase were present under these conditions, but enzymes in the glyoxylate shunt and malic enzyme were absent. Gluconeogenesis and the pentose phosphate pathway were mainly employed for biosynthesis and accounted for less than 3% of total carbon consumption. The model also indicated surprisingly high reversibility in the reaction between oxoglutarate and succinate. This step operates close to the thermodynamic equilibrium, possibly because succinate is synthesized via a transferase reaction, and the conversion of oxoglutarate to succinate is a rate-limiting step for carbon metabolism. These findings enable a better understanding of the relationship between genome annotation and extant metabolic pathways in G. metallireducens.
Kinetics of consumption of fermentation products by anode-respiring bacteria
Applied Microbiology and Biotechnology, 2007
We determined the kinetic response of a community of anode-respiring bacteria oxidizing a mixture of the most common fermentation products: acetate, butyrate, propionate, ethanol, and hydrogen. We acclimated the community by performing three consecutive batch experiments in a microbial electrolytic cell (MEC) containing a mixture of the fermentation products. During the consecutive-batch experiments, the coulombic efficiency and start-up period improved with each step. We used the acclimated biofilm to start continuous experiments in an MEC, in which we controlled the anode potential using a potentiostat. During the continuous experiments, we tested each individual substrate at a range of anode potentials and substrate concentrations. Our results show low current densities for butyrate and hydrogen, but high current densities for propionate, acetate, and ethanol (maximum values are 1.6, 9.0, and 8.2 A/m2, respectively). Acetate showed a high coulombic efficiency (86%) compared to ethanol and propionate (49 and 41%, respectively). High methane concentrations inside the MEC during ethanol experiments suggest that methanogenesis is one reason why the coulombic efficiency was lower than that of acetate. Our results provide kinetic parameters, such as the anode overpotential, the maximum current density, and the Monod half-saturation constant, that are needed for model development when using a mixture of fermentation products. When we provided no electron donor, we measured current due to endogenous decay of biomass (~0.07 A/m2) and an open-cell potential (−0.54 V vs Ag/AgCl) associated with biomass components active in endogenous respiration.
Enzyme and Microbial Technology, 1999
The aim of the present work was to investigate whether uncoupling of catabolism from anabolism, which was often observed in heterotrophic microorganisms under energy-sufficient growth conditions, also occurs in the autotrophic bacterium Methanobacterium thermoautotrophicum. For this purpose, M. thermoautotrophicum was cultivated in continuous cultures that were limited by the trace element iron. The influences of both dilution rate and iron supply rate on the coupling between anabolism and catabolism were investigated. As compared to continuous cultures of M. thermoautotrophicum limited by the energy substrate H 2 , a 5-fold decrease in the biomass concentration and a 3-fold decrease in H 2 , CO 2 , and CH 4 conversion rates were observed in iron-limited cultures. However, the specific substrate and product conversion rates increased as compared to the values determined in energy-limited cultures. Thus, iron limitation provoked an uncoupling of catabolism from anabolism. At a dilution rate of 0.096 h Ϫ1 and at an iron concentration of 17 M in the feed, the specific H 2 consumption rate was 100% higher than the rate determined under H 2 -limiting conditions, whereas at a dilution rate of 0.168 h Ϫ1 , the values differed only by 5%. Uncoupling of catabolism from anabolism also increased dramatically when the iron supply rate was lowered but the dilution rate was kept constant. Thus, the extent of uncoupling is a function of both the dilution rate and the iron supply rate. It was found that the specific consumption rate of H 2 increased in parallel with the partial pressure of H 2 in the culture medium. This suggested that the catabolic activity of M. thermoautotrophicum was not stringently controlled at the enzymatic level and can be considerably stimulated by the excess of H 2 in the medium. Hypotheses as to the fate of the excess energy derived from uncoupled catabolism are discussed, but the physiological reason for the partial uncoupling between catabolism and anabolism remains yet to be clarified. Enzyme and Microbial Technology 25 (1999) 784 -794 0141-0229/99/$ -see front matter
European Journal of Biochemistry, 1998
The energetic parameters of Escherichia coli were analyzed for the aerobic/anaerobic transition. The electrochemical proton potential (∆p) across the cytoplasmic membrane was determined in the steady state of respiration with O 2 , nitrate, fumarate, dimethylsulfoxide (Me 2 SO), and for fermentation. With O 2 , a proton potential of Ϫ160 mV was obtained. For anaerobic respiration with nitrate, fumarate or Me 2SO, ∆ p decreased only slightly by about 20 mV in contrast to earlier assumptions, whereas ∆ p dropped by approximately 40 mV during fermentation. Under all conditions, the membrane potential (∆Ψ) contributed the major portion to ∆p. The cellular ATP levels were highest for aerobic growth (about 13 µmol/g dry cells) and decreased to 3Ϫ6 µmol/g in anaerobic metabolism. ∆G′ Phos , however, was constant due to equivalent changes of the ADP contents. Transition to the stationary growth phase caused a massive drop in the ATP content. It is concluded that, during anaerobic respiration, the energetic situation for the bacteria is very similar to that for aerobic growth with respect to ∆ G′ Phos and ∆p whereas, for fermentation, a significant decrease in ∆ p was observed. The consequences for the cellular energetics and for the regulation of the aerobic/anaerobic transition are discussed.