Bacteria methane

Besides the aerobic microorganisms there are also anaerobic ones. These exist and multiply where no dissolved oxygen is present. Saprophytic bacteria produce organic acids and alcohols. The methane bacteria will then convert these compounds into cells plus carbon dioxide and methane. The methane may be recovered and binned as fuel. If any sulfur is present it will eventually be converted to H2S. 

Fundamentally new insights have recently been gained by Kluyver and Schnellen. Making use of a pure culture of methane bacteria, Methanosarcina Barkerii, they converted a mixture of carbon monoxide and hydrogen into methane according to the equation CO - - 3 H2 = H2O -F CH4. This fermentation process actually takes place in two steps (a) CO + H2O = H2 - - CO2 and (b) CO2 + 4 H2 = 2 H2O - -CH4. Many details and references to the older literature can be found in this publication and also in the thesis of Schnellen. ... 

Some volatile compounds such as methanethiol, dimethylsulfide and dimethyldisulfide have been shown to yield methane when they were added to anaerobic cultures derived from aquatic sediments (70. 71V Kiene et al. (22) showed that methane bacteria and sulfate-reducers competed for dimethyldisulfide when it was added at low concentrations to anaerobic aquatic sediments. They also isolated a methanogen that metabolized dimethyldisulfide to methane and carbon dioxide (72). Recently Oremland et al (22) detected trace amounts of ethane released from anoxic sediment slurries. This could be stimulated by the addition of ethanethiol or diethylsulfide and inhibited by the addition of bromoethanesulfonic acid which specifically inhibits methane bacteria. These results indicated that methane bacteria co-metabolized these two OSC. 

In the absence of oxygen, in a closed reactor, anaerobic bacteria ferment organic matter into methane and carbon dioxide, a mixture named biogas. Biogas is produced through the activity of common methane bacteria that cause anaerobic degradation over a broad temperature range from 10°C to over 100°C. 

The systems using the larger packing are used in the treatment of relatively strong, low-suspended-solids industrial waste. These systems are closed columns usually run in an upflow mode with a gas space at the top. These are operated under anaerobic conditions with waste conversion to methane and carbon dioxide as the goal. Effluent recycle is often used to help maintain the pH in the inlet zone in the correct range 6.5-7.5 for the methane bacteria. Some wastes require the addition of alkaline material to prevent a pH drop. Sodium bicarbonate is often recommended for pH control because it is easier to handle than lime or sodium hydroxide, and because an overdose of bicarbonate will only raise the pH modestly. An overdose of lime or sodium hydroxide can easily raise the pH above 8.0. Table 22-48 gives... 

An anaerobic digester is a no-recycle complete mix reactor. Thus, its performance is independent of organic loading but is controlled by hydraulic retention time (HRT). Based on kinetic theory and values of the pseudo constants for methane bacteria, a minimum HRT of 3 to 4 days is required. To provide a safety factor and compensate for load variation as indicated earlier, HRT is kept in the range 10 to 30 days. Thickening of feed sludge is used to reduce the tank volume required... 

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. 

Figure 1. Interrelationship between the methane bacteria and other substances of the anaerobic carbon cycle...

To date only five species of methane bacteria have been obtained in pure culture. M. vanniellii (5), Methanohacterium ruminantium (7), Methanobacterium mobilis (28), and Methanobacterium formicicum (21) grow on formate and ferment H2. The last species also ferments CO. The methanogenic symbiont of M. omelianskii, probably a variety of M. formicicum (29) grows only on H2 (16). Methanosarcina barkeri is iso-... 

The possible relationship of the methane fermentation with the more conventional examples of one-carbon metabolism as catalyzed by folate and vitamin B12 cofactors has been long apparent. 5-Methyl tetrahydro-folate, 5,10-methylene tetrahydrofolate, and methyl vitamin B12 are converted to methane by cell-free extracts of M. barkeri 32) and M. omeli-anskii (33). The involvement of vitamin B12 is further implicated by its high cellular level in methane bacteria and by the isolation of B12-containing proteins in extracts of M. barkeri 30) which stimulate methane evolution from methyl vitamin B12. The components and pathways that can be demonstrated in cell-free M. barkeri extracts 32) are listed below. 

Our present understanding of the physiology of the methane bacteria is still in a comparatively early stage of development. However, pure cultures date back only to 1947 (21) and knowledge of their intermediary metabolism has depended on the comparatively recent elucidations of the active intermediates in the transfer of one-carbon units. 

VIII. Tracer Experiments on Fatty Acid Oxidation by Methane Bacteria, /. Bacteriol, (1951) 61, 67-80. 

Monoxide by Pure Cultures of Methane Bacteria, Arch, Biochem, (1947) 14, 57-70. 

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. 

It has become clear recently that a major substrate of methane bacteria in nature is hydrogen all of the methane bacteria in pure culture in 1970 were able to use hydrogen. Many anaerobes which may be found in anaerobic waste treatment facilities produce hydrogen as a normal product of their metabolism, yet the amount of hydrogen detectable in sludge digesters is very low, an indication that it may be an important intermediate in methane formation. 

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