Extrapolating from extensive field measurements on foliar emissions in the U.S. approximate global inputs of isoprene and terpenes of 3.5 times 10 to the 14th power and 4.8 times 10 to the 14th power g(C)/yr, respectively, are obtained. The oxidation of these hydrocarbons could contribute in an important way to the atmospheric sources of CO (4.2-13.3 times 10 to the 14th power g/yr) and H2 (10-35 times 10 to the 12th power g/yr), and to organic species soluble in rainwater

Estimates on the production of CO and H2 from the oxidation of hydrocarbon emissions from vegetation

The latitudinal and seasonal variation of ozone in the troposphere is discussed. Of particular interest is the asymmetrical behavior of this gas with respect to the two hemispheres. These asymmetries, when coupled with a diagnostic photochemical model of the troposphere, lends support to the view that ozone cannot be viewed as an inert tracer of stratospheric origin. We note in our calculations that it is likely that the budgets of carbon monoxide and tropospheric ozone may be quite dependent on each other and discuss these calculations in light of the uncertainty which currently exists about representative global tropospheric background concentrations of the nitrogen oxides. In addition, the seasonal variation of excess 14 CO 2 (a stratospheric tracer) is examined and compared with the seasonal ozone variation during the same period of observations at the same location and altitudes. The distinct maxima for ozone found during the summer in the lower troposphere are not present for the 14 CO 2 data. This finding likewise suggests that photochemical processes taking place in the troposphere are an important source term for tropospheric ozone. DOI: 10.1111/j.2153-3490.1979.tb00922.x

Observational and theoretical evidence in support of a significant in‐situ photochemical source of tropospheric ozone

Different species of methanogenic bacteria growing on CO2 and H2 were shown to remove CO added to the gas phase. Rates up to 0.2 μmol of CO depleted/min per 10 ml of culture containing approximately 7 mg of cells (wet weight) were observed. Methanobacterium thermoautotrophicum was selected for further study based on its ability to grow rapidly on a completely mineral medium. This species used CO as the sole energy source by disproportionating CO to CO2 and CH4 according to the following equation: 4CO + 2H2O → 1CH4 + 3CO2. However, growth was slight, and the growth rate on CO was only 1% of that observed on H2/CO2. Growth only occurred with CO concentrations in the gas phase of lower than 50%. Growth on CO agrees with the finding that cell-free extracts of M. thermoautotrophicum contained both an active factor 420 (F420)-dependent hydrogenase (7.7 μmol/min per mg of protein at 35°C) and a CO-dehydrogenating enzyme (0.2 μmol/min per mg of protein at 35°C) that catalyzed the reduction of F420 with CO. The properties of the CO-dehydrogenating enzyme are described. In addition to F420, viologen dyes were effective electron acceptors for the enzyme. The apparent Km for CO was higher than 1 mM. The reaction rate increased with increasing pH and displayed an inflection point at pH 6.7. The temperature dependence of the reaction rate followed the Arrhenius equation with an activation energy (ΔH‡) of 14.1 kcal/mol (59.0 kJ/mol). The CO dehydrogenase activity was reversibly inactivated by low concentrations of cyanide (2 μM) and was very sensitive to inactivation by oxygen. Carbon monoxide dehydrogenase of M. thermoautotrophicum exhibited several characteristic properties found for the enzyme of Clostridium pasteurianum but differed mainly in that the clostridial enzyme did not utilize F420 as the electron acceptor.

Carbon Monoxide Oxidation by Methanogenic Bacteria

Atmospheric sulphur: Natural and man-made sources

Reduced inorganic sulfur compounds are oxidized by members of the domains Arehaea and Bacteria. These compounds are used as electron donors for anaerobic phototrophic and aerobic chemotrophic growth, and are mostly oxidized to sulfate. Different enzymes mediate the conversion of various reduced sulfur compounds. Their physiological function in sulfur oxidation is considered (i) mostly from the biochemical characterization of the enzymatic reaction, (ii) rarely from the regulation of their formation, and (iii) only in a few cases from the mutational gene inactivation and characterization of the resulting mutant phenotype. In this review the sulfur-metabolizing reactions of selected phototrophic and of chemotrophic prokaryotes are discussed. These comprise an archaeon, a cyanobacterium, green sulfur bacteria, and selected phototrophic and chemotrophic proteobacteria. The genetic systems are summarized which are presently available for these organisms, and which can be used to study the molecular basis of their dissimilatory sulfur metabolism. Two groups of thiobacteria can be distinguished: those able to grow with tetrathionate and other reduced sulfur compounds, and those unable to do so. This distinction can be made irrespective of their phototrophic or chemotrophic metabolism, neutrophilic or acidophilic nature, and may indicate a mechanism different from that of thiosulfate oxidation. However, the core enzyme for tetrathionate oxidation has not been identified so far. Several phototrophic bacteria utilize hydrogen sulfide, which is considered to be oxidized by flavocytochrome c owing to its in vitro activity. However, the function of flavocytochrome c in vivo may be different, because it is missing in other hydrogen sulfide-oxidizing bacteria, but is present in most thiosulfate-oxidizing bacteria. A possible function of flavocytochrome in the operon encoding enzymes involved in thiosulfate oxidation of Paracoccus denitrificans. Adenosine-5′-phosphosulfate reductase thought to function in the ‘reverse’ direction in different phototrophic and chemotrophic sulfur-oxidizing bacteria was analysed in Chromatium vinosum. Inactivation of the correspondig gene does not affect the sulfite-oxidizing ability of the mutant. This result questions the concept of its ‘reverse’ function, generally accepted for over three decades.

Physiology and Genetics of Sulfur-oxidizing Bacteria

Some trace gases are contained in the atmosphere in appreciable amounts: methane, carbon monoxide, hydrogen, nitrous oxide. The bulk of these gases is of biological origin. Hydrogen is a primary product of microbial metabolism under anaerobic conditions. However, before reaching the atmosphere, it is converted by methane bacteria to methane, by nitrate reducing bacteria to nitrogen and to nitrous oxide and by sulfate reducing bacteria to hydrogen sulfide. Carbon monoxide is produced from certain organic compounds. Hydrogen, methane, and carbon monoxide are quickly oxidized by microorganisms under aerobic conditions. However, especially methane and carbon monoxide reach the atmosphere. The literature dealing with the microorganisms and biochemical reactions involved in the production and conversion of trace gases is reviewed. DOI: 10.1111/j.2153-3490.1974.tb01947.x

https://www.tandfonline.com/doi/pdf/10.3402/tellusa.v26i1-2.9732

H. G. Schlegel

Papers

Production, modification, and consumption of atmospheric trace gases by microorganisms