Anaerobic Carbon Monoxide Research Articles

Anaerobic transformation of carbon monoxide by microbial communities of Kamchatka hot springs

Carbon monoxide (CO) is one of the common gaseous compounds found in hot volcanic environments. It is known to serve as the growth substrate for a number of thermophilic prokaryotes, both aerobic and anaerobic. The goal of this work was to study the process of anaerobic transformation of CO by microbial communities inhabiting natural thermal environments: hot springs of Uzon Caldera, Kamchatka. The anaerobic microbial community of Treshchinny Spring (80°C, pH 6.5) was found to exhibit two peaks of affinity for CO (K (S1)=54nM and K (S2)=1μM). The actual rate of anaerobic CO transformation by the microbial community of this spring, calculated after obtaining the concentration dependence curve and extrapolated to the natural concentration of CO dissolved in the hot spring water (20nM), was found to be 120μmoll(-1) of sediment day(-1). In all the hot springs studied, more than 90% of the carbon of (14)CO upon anaerobic incubation was recovered as (14)CO(2). From 1 to 5% of (14)CO was transformed to volatile fatty acids (VFA). The number of microorganisms capable of anaerobic CO oxidation determined by dilution-to-extinction method reached 10(6)cellsml(-1) of sediment. CO-transforming anaerobic thermophilic microorganisms isolated from the springs under study exhibited hydrogenogenic type of CO oxidation and belonged to the bacterial genera Carboxydocella and Dictyoglomus. These data suggest a significant role of hydrogenogenic carboxydotrophic prokaryotes in anaerobic CO transformation in Uzon Caldera hot springs.

‘That which does not kill us only makes us stronger’: the role of carbon monoxide in thermophilic microbial consortia

Carbon monoxide (CO), while a potent toxin, is also a key intermediate in major autotrophic pathways such as methanogenesis and acetogenesis. The ability of purple sulfur bacteria to use CO as an energy source was first described by Uffen in 1976. The prototype extremely thermophilic carboxydotroph Carboxydothermus hydrogenoformans was described in 1991. Eight bacteria and one archaeon that utilize CO have since been isolated and described from diverse geothermal environments. They derive energy from the oxidation of CO with water to form CO(2) and H(2). Most of these isolates thrive with headspace CO partial pressures around 1 atm, which is grossly elevated relative to CO concentrations in geothermal effluents. To account for this, we suggest that under consortial growth conditions the carboxydotrophs occupy microniches in which biogenic CO accumulates locally to high concentrations. CO oxidizers dissipate these potentially toxic CO hot spots with the production of H(2), CO(2) and acetate whose subsequent oxidation fuels other thermophiles. The identification of genes related to anaerobic CO oxidation in many metagenomic databases attests to widespread distribution of carboxydotrophs. Current evidence suggests that CO-oxidizing bacteria and archaea hold a vital niche in thermophilic ecosystems.

Carbon Dioxide Activation at the Ni,Fe-Cluster of Anaerobic Carbon Monoxide Dehydrogenase

Anaerobic CO dehydrogenases catalyze the reversible oxidation of CO to CO2 at a complex Ni-, Fe-, and S-containing metal center called cluster C. We report crystal structures of CO dehydrogenase II from Carboxydothermus hydrogenoformans in three different states. In a reduced state, exogenous CO2 supplied in solution is bound and reductively activated by cluster C. In the intermediate structure, CO2 acts as a bridging ligand between Ni and the asymmetrically coordinated Fe, where it completes the square-planar coordination of the Ni ion. It replaces a water/hydroxo ligand bound to the Fe ion in the other two states. The structures define the mechanism of CO oxidation and CO2 reduction at the Ni-Fe site of cluster C.

Life in Hot Carbon Monoxide: The Complete Genome Sequence of Carboxydothermus hydrogenoformans Z-2901

We report here the sequencing and analysis of the genome of the thermophilic bacterium Carboxydothermus hydrogenoformans Z-2901. This species is a model for studies of hydrogenogens, which are diverse bacteria and archaea that grow anaerobically utilizing carbon monoxide (CO) as their sole carbon source and water as an electron acceptor, producing carbon dioxide and hydrogen as waste products. Organisms that make use of CO do so through carbon monoxide dehydrogenase complexes. Remarkably, analysis of the genome of C. hydrogenoformans reveals the presence of at least five highly differentiated anaerobic carbon monoxide dehydrogenase complexes, which may in part explain how this species is able to grow so much more rapidly on CO than many other species. Analysis of the genome also has provided many general insights into the metabolism of this organism which should make it easier to use it as a source of biologically produced hydrogen gas. One surprising finding is the presence of many genes previously found only in sporulating species in the Firmicutes Phylum. Although this species is also a Firmicutes, it was not known to sporulate previously. Here we show that it does sporulate and because it is missing many of the genes involved in sporulation in other species, this organism may serve as a “minimal” model for sporulation studies. In addition, using phylogenetic profile analysis, we have identified many uncharacterized gene families found in all known sporulating Firmicutes, but not in any non-sporulating bacteria, including a sigma factor not known to be involved in sporulation previously.

Carbon monoxide consumption and production by wetland peats

Wetland peats were analyzed for their potential to consume and produce carbon monoxide (CO) under aerobic and anaerobic conditions. Kinetic and functional characteristics of anaerobic CO consumption were compared with those of methanogenesis. Inhibitors of methanogenesis and sulfate reduction decreased the rate of CO consumption by 30 and 20%, respectively, suggesting that methanogens and sulfate reducers played secondary roles in CO uptake. Low concentrations of nitrate (0.2 mM) stimulated CO uptake, while high concentrations (20 mM) were partially inhibitory. Sulfate (20 mM), ferric iron (60 μmol cm−3), and acetate (10 mM) had no effect on CO consumption. Formate and glucose (10 mM) temporarily stimulated net CO and H2 production. Aerobic incubations of previously anaerobic peat stimulated transient CO production. Kinetic analysis of anaerobic CO consumption by two sediment types (organic peat and mineral silt) showed that maximum potential uptake velocities (Vmaxp) in each sediment were similar, 1–2 nmol CO cm−3 sediment h−1, with apparent half saturation constants (Kapp) ranging from 5 to 37 nM CO. Anaerobic CO consumption may limit CO accumulation in wetland peats and sediments, thereby affecting CO emissions. Understanding the role and characteristics of wetland CO consumption may help explain current and future patterns in wetland CO dynamics.

Carbon monoxide consumption and production by wetland peats

Wetland peats were analyzed for their potential to consume and produce carbon monoxide (CO) under aerobic and anaerobic conditions. Kinetic and functional characteristics of anaerobic CO consumption were compared with those of methanogenesis. Inhibitors of methanogenesis and sulfate reduction decreased the rate of CO consumption by 30 and 20%, respectively, suggesting that methanogens and sulfate reducers played secondary roles in CO uptake. Low concentrations of nitrate (0.2 mM) stimulated CO uptake, while high concentrations (20 mM) were partially inhibitory. Sulfate (20 mM), ferric iron (60 μmol cm −3), and acetate (10 mM) had no effect on CO consumption. Formate and glucose (10 mM) temporarily stimulated net CO and H 2 production. Aerobic incubations of previously anaerobic peat stimulated transient CO production. Kinetic analysis of anaerobic CO consumption by two sediment types (organic peat and mineral silt) showed that maximum potential uptake velocities ( V maxp) in each sediment were similar, 1–2 nmol CO cm −3 sediment h −1, with apparent half saturation constants ( K app) ranging from 5 to 37 nM CO. Anaerobic CO consumption may limit CO accumulation in wetland peats and sediments, thereby affecting CO emissions. Understanding the role and characteristics of wetland CO consumption may help explain current and future patterns in wetland CO dynamics.

98/02860 Procedure and apparatus for manufacture of hydrogen-carbon monoxide gas mixture: Kiso, F. Ger. Offen. DE 19,634,857 (Cl. C10J3/46), 6 Mar 1997, JP Appl. 95/222,990, 31 Aug 1995, 25 pp. (In German)

Wetland peats were analyzed for their potential to consume and produce carbon monoxide (CO) under aerobic and anaerobic conditions. Kinetic and functional characteristics of anaerobic CO consumption were compared with those of methanogenesis. Inhibitors of methanogenesis and sulfate reduction decreased the rate of CO consumption by 30 and 20%, respectively, suggesting that methanogens and sulfate reducers played secondary roles in CO uptake. Low concentrations of nitrate (0.2 mM) stimulated CO uptake, while high concentrations (20 mM) were partially inhibitory. Sulfate (20 mM), ferric iron (60 μmol cm−3), and acetate (10 mM) had no effect on CO consumption. Formate and glucose (10 mM) temporarily stimulated net CO and H2 production. Aerobic incubations of previously anaerobic peat stimulated transient CO production. Kinetic analysis of anaerobic CO consumption by two sediment types (organic peat and mineral silt) showed that maximum potential uptake velocities (Vmaxp) in each sediment were similar, 1–2 nmol CO cm−3 sediment h−1, with apparent half saturation constants (Kapp) ranging from 5 to 37 nM CO. Anaerobic CO consumption may limit CO accumulation in wetland peats and sediments, thereby affecting CO emissions. Understanding the role and characteristics of wetland CO consumption may help explain current and future patterns in wetland CO dynamics.

Carbon-monoxide oxidation in cell-free extracts of Clostridium pasteurianum.

Cell-free extracts of NH4-grown and N2-grown Clostridium pasteurianum were found to catalyze the oxidation of carbon monoxide to CO2 under strictly anaerobic conditions. Free formate was not an intermediate. FAD, FMN, methylene blue and viologen dyes were effective as electron acceptors, while NAD+, NADP+ or oxidized ferredoxin were ineffective. The reaction was routinely followed by measuring the reduction of methyl viologen with carbon monoxide photometrically. The rate of carbon monoxide oxidation followed simple Michaelis-Menten kinetics. 0.1–0.2 μmol carbon monoxide was oxidized by methyl viologen per min and mg soluble protein at pH 8.7. Half-maximal velocities were obtained with 5 μM carbon monoxide and 0.4 mM methyl viologen. The rate increased with increasing pH with an inflection point near pH 8.4. The carbon monoxide oxidizing activity was acid-labile (pH 4.5), precipitable with acids at pH 5 and sensitive to molecular oxygen. It was relatively stabile to heat. At 90 °C only 50%, of the activity were destroyed within 15 min. Incubation of the extracts with cyanide (10 μM) or with methyl iodide (2.5 mM) resulted in a reversible loss of the carbon monoxide oxidizing activity. The rate and extent of inactivation by cyanide was decreased in the presence of carbon monoxide by a factor of 100 and 10, respectively. On the contrary, the rate of inactivation by methyl iodide was increased in the presence of carbon monoxide by a factor of 6. The activity of extracts inactivated by cyanide in the absence of carbon monoxide was partially restored by incubation of the extracts with carbon monoxide; the inactivation by methyl iodide was reversed by exposure of the extracts to the light of a projection lamp. These properties are taken to indicate that a vitamin B12 compound is probably involved in the catalysis of anaerobic carbon monoxide oxidation.