Methane bacteria reactions

A partial and abbreviated scheme showing the interrelationship between the methane bacteria and other representatives of the anaerobic carbon cycle is listed in Figure 1. The heavy arrows indicate methane fermentations by individual species or perhaps in some cases by closely dependent symbiotes. The remaining reactions of Figure 1 are catalyzed by propionibacteria, clostridia, butyribacteria, and other anaerobes. The general references of Wood (13), Barker (4), and Stadtman (14) may be consulted for further details and additional fermentations. 

It is not known how ATP is formed in methane bacteria an ATP-yielding reaction has not been documented in cell extracts. A recent effort by Roberton to examine ATP pools in hydrogen-grown Methano-hacterium has shown that energy conversion is very inefficient (5). 

Methane bacteria have been shown to catalyze reactions in which the active methyl group is transferred to acceptors such as arsenate or mercury. When extracts are incubated in a hydrogen atmosphere with methylcobalamin, arsenate, and ATP, a volatile arsine derivative is formed (20). Arsines are difficult and dangerous to work with they are extremely poisonous and are oxidized rapidly in air. Fortunately they have an intense garhc odor so the investigator is warned of their presence. 

The present studies confirm the earlier studies indicating the relatively great biosynthetic abilities of the methane bacteria and suggest that much of the cellular carbon compounds are probably synthesized from acetate and carbon dioxide. In view of the carbon dioxide and acetate requirements and the reductive carboxylation reactions shown to be involved in isoleucine synthesis in M. ruminantium (26) and the probability of similar carboxylation reactions in biosynthesis of isoleucine, alanine, and other amino acids in MOH, suggested by the studies on M. omelianskii (34), the operation of the pyruvate synthase reaction and some other reactions of the reductive carboxylic acid cycle (35, 36) as major pathways of biosynthesis of cellular materials in these bacteria is an attractive hypothesis. 

The studies of McCarty and co-workers have shown clearly that volatile acids are not toxic to methane bacteria at concentrations that would occur in stuck or sour digesters. On the contrary, evidence has been elucidated which indicates propionate retards the acid formers. Thus, the use of alkaline substances to maintain an adequate buffer capacity in an anaerobic waste treatment unit is a valid procedure. A word of caution is necessary pH control is not a universal palliative. Its only advantage is to prevent a bad situation from getting out of hand. The basic cause of the digester biochemical imbalance must be discovered and rectified. Unless this is done, pH control is worthless in the long run. In addition, care must be exercised in selecting an alkaline material that will not produce a toxic reaction. 

Gas Flow Rate. The model can be extended to consider all five desired variables, and the restriction of a constant partial pressure of carbon dioxide can be removed by developing material balances for carbon dioxide in both the liquid and gas phases. The material balance on dissolved carbon dioxide is shown in Equation 25. Rb is the rate of production of carbon dioxide from the substrate by the methane bacteria and Rc is the rate of production of carbon dioxide from bicarbonate. The reaction of substrate and bicarbonate to produce carbon dioxide is given in Equation 28. 

Application of this process to furfural waste water was studied in detail by Wirtz and Dague [44]. Contrary to widespread erroneous belief, these authors established beyond any doubt that at the concentrations occurring in furfural waste water, the toxicity of furfural for some microorganisms does not apply to methane bacteria. They not only thrive on acetic acid but eat up furfural as well. For the low concentrations of acetic acid in furfural waste water, these bacteria, known to decompose acetic acid to methane and carbon dioxide according to the reaction... 

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. 

The lower than expected yields can be explained by the nature of methane oxidation to methanol in these bacteria. This reaction, catalysed by methane mono-oxygenase, is a net consumer of reducing equivalents (NADH), which would otherwise be directed to ATP generation and biosynthesis. In simple terms the oxidation of methane to methanol consumes energy, lowering the yield. 

In some cases, microorganisms can transform a contaminant, but they are not able to use this compound as a source of energy or carbon. This biotransformation is often called co-metabolism. In co-metabolism, the transformation of the compound is an incidental reaction catalyzed by enzymes, which are involved in the normal microbial metabolism.33 A well-known example of co-metabolism is the degradation of (TCE) by methanotrophic bacteria, a group of bacteria that use methane as their source of carbon and energy. When metabolizing methane, methanotrophs produce the enzyme methane monooxygenase, which catalyzes the oxidation of TCE and other chlorinated aliphatics under aerobic conditions.34 In addition to methane, toluene and phenol have been used as primary substrates to stimulate the aerobic co-metabolism of chlorinated solvents. 

Hurst, G. B. Weaver, K. Doktycz, M. I Buchanan, M. V. Costello, A. M. Lidstrom, M. E. MALDI-TOF analysis of polymerase chain reaction products from methan-otrophic bacteria. Anal. Chem. 1998, 70, 2693-2698. 

The methane-metabolising autotrophic bacteria derive energy from the reaction ... 

Copper enzymes are involved in reactions with a large number of other, mostly inorganic substrates. In addition to its role in oxygen and superoxide activation described above, copper is also involved in enzymes that activate methane, nitrite and nitrous oxide. The structure of particulate methane mono-oxygenase from the methanotrophic bacteria Methylococcus capsulatus has been determined at a resolution of 2.8 A. It is a trimer with an a3P33 polypeptide arrangement. Two metal centres, modelled as mononuclear and dinuclear copper, are located in the soluble part of each P-subunit, which resembles CcOx subunit II. A third metal centre, occupied by Zn in the crystal, is located within the membrane. 

---