Methanotrophs methane-oxidizing

Oremland et al. [136] subsequently demonstrated that methane-oxidizing bacteria also had the capacity to co-oxidize methyl bromide by methane monooxygenase produced during the oxidation of methane to methanol. They also showed that methanotrophic soils that had a high capacity to oxidize methane degraded14C-labeled methyl bromide to 14C02. 

Calculate the steady-state output trichloroethene concentration (/tM) after the methanotrophs have increased their biomass to a steady state level (cell-m-3) assuming a tank with a volume of either V= 10 m3 or 50 m3. Assume you have a waste water flow, Q, of 5 m3 d l, a microbial inoculum with growth properties like those shown in Table 17.6 for the landfill-derived methane oxidizers, and a die-off coefficient b of 0.1 d . 

Girnis P.R. Orphan V.J. Hallam S.J. and DeLong E.F. (2003). Growth and methane oxidation rates of anaerobic methanotrophic archaea in a continuous-flow bioreactor. Applied and Environmental Microbiology, 69, 5472- 5482. 

Methane-oxidizing bacteria, or methanotrophs, can play a central role in reducing CH4 emissions from estuaries, by converting CH4 into bacterial biomass or CO2 (Topp and Hanson, 1991). It has been estimated that methanotrophic bacteria in freshwater... 

Methanotrophic bacteria use methane as the sole source of carbon and energy employing MMO to catalyze the first step in the methane oxidation pathway leading ultimately to CO2. 

Methane oxidation can be limited by nitrogen due to enzyme-level inhibition or unmet metha-notroph nitrogen demand. The oxidation of CH4 by methanotrophic bacteria and by... 

Dedysh S. N., Liesack W., Khmelenina V. N., Suzina N. E., Trotsenko Y. A., Semrau J. D., Bares A. M., Panikov N. S., and Tiedje J. M. (2000) Methylocella palustris gen. nov., sp. nov., a new methane-oxidizing acidophihc bacterium from peat bogs representing a novel sub-type of serine pathway methanotrophs. Int. J. Syst. Evol. Microbiol. 50, 955—969. 

Methane is oxidized under aerobic conditions by a group of bacteria called methanotrophs. These widespread bacteria play an important role in the global cycling of methane. Two types of methane oxidation systems are known, a ubiquitous particulate methane monooxygenase (pMMO) and a cytoplasmic soluble methane monooxygenase (sMMO) found in only a few strains. These enzymes have different catalytic characteristics, and so it is important to know the conditions under which each is expressed. In those strains containing both sMMO and pMMO, the available copper concentration controls which enzyme is expressed. However, the activity of the pMMO is also affected by copper. Data on methane oxidation in natural samples suggest that methanotrophs are not copper-limited in nature and express the pMMO predominantly. 

The aerobic oxidation of methane is carried out by bacteria called methanotrophs (1). These bacteria grow on methane as their sole carbon and energy source, oxidizing a portion of the methane to C02 and fixing a portion into cell material. They are obligate aerobes because the methane oxidation reaction requires molecular oxygen. 

Methanotrophs, which are widespread in aquatic and terrestrial environments, carry out methane oxidation in most habitats where methane and oxygen coexist (3). On a global scale, these bacteria are responsible for a major portion of the biological methane consumption that occurs on the earth s surface. Therefore, a great deal of interest exists concerning their role in global methane cycling (4). 

To understand the role of these bacteria in methane cycling, the methane oxidation system must be studied. In methanotrophs, methane is oxidized to methanol by an enzyme called the methane monooxygenase (MMO) (I), which uses methane, molecular oxygen, and reducing equivalents to produce methanol and water. All known methanotrophs contain a membrane-bound MMO, called the particulate methane monooxygenase (pMMO). The presence of this enzyme system is correlated with the complex internal membrane system found in all known methanotrophs. 

In my laboratory we studied the effect of copper on whole cells of meth-anotrophs. These experiments involved growing different pure cultures of methanotrophs in medium containing different initial amounts of copper, added as copper sulfate, as described previously (9), and analyzing both growth rate and methane oxidation kinetics. We did not measure free copper in these experiments, so the effects noted have not yet been correlated to copper speciation but rather to total copper added at the start of growth. 

These data show that the copper concentration available to growing cells not only determines whether the pMMO will be expressed, but strongly influences the kinetics of methane oxidation by whole cells containing the pMMO (Table III). This information has potentially important environmental implications. If methanotrophs were copper-limited in nature, we would expect to observe high whole-cell Ks values because of expression of sMMO and the copper-deficient pMMO. This situation should result in a poor ability of natural populations to survive at low (submicromolar) methane concentrations. Alternatively, if they are not copper-limited, the Ks values should be lower, improving the ability of these cells to grow at submicromolar methane concentrations. 

In summary, the information available to date indicate that copper is a major regulatory parameter for methane oxidation in methanotrophs. Not only does it regulate the expression of sMMO and pMMO in those strains that contain both, it also controls the kinetics of methane oxidation by the pMMO. 

These findings have important implications for methane oxidation in natural samples. First, they suggest that the pMMO is the predominant enzyme system for methane oxidation in natural populations and thus provide more impetus for understanding this enzyme system. Second, the response of natural populations to changes in methane concentrations will most likely depend on a complex set of parameters, of which available copper concentration may be the key. It is now important to study how methanotrophs utilize copper and how they respond to changes in copper and methane concentrations and to copper speciation, in order to predict how natural populations will respond to environmental perturbations. 

The methanotrophic bacteria have one known pathway for aerobic methane oxidation to CO2 31, 42,123). MMO catalyzes the first energetically difficult step in the formation of methanol from methane. The second step is catalyzed by methanol dehydrogenase (with a PQQ cofactor) and results in formation of formaldehyde, which is then converted by formaldehyde dehydrogenase (with no known cofactor) to formate. Finally, carbon dioxide is produced by formate dehydrogenase (with five different iron-sulfur clusters, a Mo-pterin cofactor, and an unusual flavin) 31, 42, 123). MMOs have a unique ability to oxidize a broad range 31,42,128,129) of hydrocarbons in addition to methane. One other system with a similar broad substrate utilization is the monoheme cytochrome P450 family, but in this case different isozymes show different specific activities (31). For soluble MMO, one single... 

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