Carbon monoxide oxidation by algae
Abstract
A metabolic reaction whereby CO is oxidized to CO2 has been shown to take place in a variety of green algae. The investigation of this reaction was facilitated by the use of 14CO. The reaction was found to be oxygen dependent with the maximal rate being obtained when the gas phase was approx. 1% O2. Although oxidation of CO was observed in the dark, the rate was increased by several fold in the presence of low-intensity light. The optimal pH of the reaction was found to be approx. 7. The Km for the reaction was measured and found to be 0.32 atm. There was an inhibition of the reaction by cyanide, azide, hydroxylamine, 3,4-dichlorophenyl-1, 1-dimethylurea, and formate. On the basis of a study of the reaction products using paper chromatography, it was concluded that CO2 was the primary product.
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Carbon monoxide consumption in upland boreal forest soils
2001, Soil Biology and BiochemistryBiological consumption by aerobic soils is an important, but poorly understood sink for carbon monoxide, a chemically active atmospheric trace gas. We used laboratory experiments to characterize CO consumption in representative soils of the northern boreal forest. This ecozone may be important in atmospheric CO consumption because it occupies 13% of the world's landmass. Soils initially showing net CO consumption emitted CO following biocidal treatment (ethylene oxide or γ-irradiation), indicating that CO consumption was biologically mediated. The use of selective inhibitors (cycloheximide, streptomycin) suggested that both prokaryotes and eukaryotes were responsible. Soil profiles generally indicated net consumption of atmospheric CO to a depth of 15 cm (concentrations decreasing from ~150 to <20 nl l−1 with depth) and a dynamic equilibrium between CO production and consumption in deeper soils (concentrations nearly constant at <20 nl l−1). Soils to a depth of 30 cm showed vigorous CO-consuming activity, suggesting that local CO production provided necessary substrate beneath the 15 cm surface zone of atmospheric influence. Radiotracer experiments demonstrated that only 5–7% of assimilated 14CO was incorporated into biomass in 5 cm core sections taken to 30 cm and that <1% of assimilated 14CO was incorporated into cellular material by a methanotroph isolated from this soil. Collectively, these data point to nonutilitarian oxidation of CO by a diverse microbial community. Carbon monoxide oxidation increased with increasing temperature over the range 4–34°C, with a Q10 of 1.8. Apparent half-saturation constants (8–36 (μl CO l−1), and maximum rates of CO consumption (0.7–2.7 μg g dry soil−1 h−1) were comparable to reports for diverse temperate soil environments, pointing to a fundamental similarity among CO-consuming microbial communities in aerobic soils.
Sinks and environmental impacts for atmospheric carbon monoxide
1995, Applied EnergyCarbon monoxide is one of the main reactive trace gases in the earth's atmosphere: it influences the atmospheric chemistry as well as the climate. In order to evaluate the atmospheric budget for carbon monoxide, a knowledge of its destruction/uptake rates by the individual sinks is required. In this study, our current understanding of sinks for atmospheric carbon monoxide is discussed. Although the major sinks have been identified, estimates for their strengths are still uncertain. Experimental data are available for only a few locations, and more measurements in representative regions world-wide are required in order to evaluate the CO global budget more accurately.
Our current understanding of the environmental impacts of carbon monoxide is reviewed. CO is a toxic gas which can cause fatal asphyxiation. However, our knowledge of the effects of exposure to moderate doses of CO on the health and behaviour of humans is limited. Carbon monoxide also contributes indirectly to global warming and ozone depletion. So, there is a need for a better understanding of the atmospheric chemical processes involving CO in order to reduce the uncertainties in the estimates of its impact on the global environment.
Sources of atmospheric carbon monoxide
1994, Applied EnergyCarbon monoxide (CO) is one of the main reactive trace gases in the earth's atmosphere: it influences both the atmospheric chemistry and the climate. In order to evaluate the atmospheric budget of CO, knowledge of the emission rates from, and the, geographic distribution of, the individual sources are required.
CO is released into the atmosphere naturally and anthropogenically: at present, the emission rates from these two categories of sources are comparable. However, the rates of emission from man-made sources have been increasing steadily since industrialisation began, and are expected to continue growing with changes in population and economy. Although the major sources of CO are known, estimates for their emission rates are still uncertain. Experimental data are available only for a limited number of locations, and more measurements in representative regions world-wide are required in order to evaluate the CO global budget more accurately.
The rapid oxidation of atmospheric CO to CO<inf>2</inf> by soils
1985, Soil Biology and BiochemistryGas exchange rates over soils were measured in a closed, flowing-gas system. 14CO was rapidly oxidized to 14CO2 with only a minor loss in atmospheric radioactivity. Incorporation of 14C into the soil was slight and was via 14CO2 rather than 14CO. CO oxidation was a microbial process and no oxidation occurred when soils had been autoclaved. The rate of CO depletion was concentration dependent and followed Michaelis-Menten kinetics. The rate constants Km and Vmax ranged from 18 to 51 μ 1−1 CO and from 0.58 to 4.35 mg C kg−1 dry soil h−1 respectively. The maximum rate of reaction for Hubbard Brook soil was about an order of magnitude greater than any soil previously reported. The oxidation reaction was accompanied initially by a reduction in net soil respiration. This was then followed by a period of high respiration which continued until CO levels were reduced to about 5μll−1. Thereafter respiration fell below the pretreatment rate and only returned to that rate 45 min after CO had been depleted from the atmosphere. The data suggest that at high CO concentrations (40–100 μll−1CO) autotrophic carboxydobacteria comprise the main component of the CO-oxidizing population and, as the concentration declines towards ambient levels they are replaced by heterotrophic microorganisms possessing a cometabolic process.
Oxidation of Carbon Monoxide by Bacteria
1983, International Review of CytologyThis chapter discusses the oxidation of carbon monoxide (CO) by bacteria. The CO generated in soil and in the lower layers of the atmosphere is oxidized to CO2 locally by biological agents, principally microbes. CO is added to the atmosphere in significant amounts through the incomplete combustion of fossil fuels and by atmospheric reactions. Bacteria that oxidize CO may be subdivided according to their ability to use CO as an energy source for growth (utilitarian oxidation) or based on whether the oxidation process is a gratuitous one (nonutilitarian oxidation) resulting from the acceptance of CO as a pseudosubstrate for an enzyme system evolved to catalyze another process. CO is inhibitory for all aerobic respiratory organisms. Even in aerobic carboxydobacteria, the high concentrations of CO reduce the growth rate and cellular yield, thereby indicating that CO tolerance is a necessary part of the ability to use CO at higher concentrations. Phototrophic bacteria may remove significant amounts of CO formed during the degradation of photosynthetic pigments in decaying vegetative materials in anaerobic sediments. The chapter also discusses the applications of the bacterial CO oxidation.
Metabolism of Carbon Monoxide by the Colonic Flora of Humans
1982, GastroenterologyThe metabolism of carbon monoxide by the colonic flora was investigated using human fecal homogenates. During anaerobic incubation, these homogenates rapidly consumed added carbon monoxide reducing the PCO level to a minimum of about 0.2 ppm. In the presence of glucose, carbon monoxide consumption averaged about 0.7 ml/h · g feces and without glucose about 0.2 ml/h · g feces. This consumption was not observed if the homogenates were autoclaved, passed through a bacterial filter, or cultured aerobically, indicating that the carbon monoxide was removed by the metabolism of fecal anaerobes. Aerobic incubation of fecal homogenates resulted in slow but definite release of carbon monoxide. While bacterial carbon monoxide consumption probably does not play an appreciable role in the turnover of carbon monoxide that is inhaled or exogenously produced, it is possible that carbon monoxide uptake by colonic flora protects other fecal organisms and possibly the host from carbon monoxide liberated in the gut.