MadSci Network: Microbiology

Re: What kind of bacteria decompose animal wastes into methane gas?

Date: Sat Mar 9 04:06:29 2002
Posted By: Andrew D. Brabban, Faculty, Biology, The Evergreen State College
Area of science: Microbiology
ID: 1010974590.Mi

The production of methane from animal wastes is a complex process 
involving many organisms from many different species. The basic process 
can however be broken down into 2 basic distinct phases. 1st, there are a 
range of organisms that ferment the large carbohydrate based wastes down 
into smaller acidic wastes. For example glucose can be fermented to 
formate, hydrogen gas, acetate, propionate, butyrate, ethanol, acetone 
etc. These organisms are generally anaerobic bacteria and these reactions 
occur for the most part in the absence of oxygen. 2nd, these products can 
then be used by another physiological group of organisms, the methanogens 
that actually produce the methane from these acidic compounds.
These reactions are found anywhere that oxygen is absent. Classic 
environments for methanogensis are swamps, anaerobic sewage digesters, 
dead trees, anything that is water logged, the guts of animals such as us, 
horses, termites, and refuse sites. These organisms are therefore present 
everywhere that oxygen is absent and carbohydrates are present. This is 
why today refuse sites collect the methane produced.
If you want to work or examine these organisms, you therefore have to 
develop methods to work in the absence of oxygen because not only do these 
organism need oxygen to be absent for them to grow but it is highly toxic 
to them binding to their enzymes and killing them. If you wanted to work 
with these bacteria you can isolate them from any marsh but you need 
methods to get rid of any oxygen, and as our atmosphere contains 21% 
oxygen this can be difficult. You can see the work of methanogens however 
easily in the wild. When you stand on a waterlogged march and the gas 
bubbles rise, these are a mixture of carbon dioxide and methane. You can 
even repeat Volta's famous methane experiment. If you are really 
interested in methanogensis a book I recommend you look at is Brocks 
Biology of Microorganisms which has a lot of information about the process.
Finally is it feasible to fermenter animal wastes to methane? Yes thatís 
what a sewage plant does with its anaerobic digesters but it can be 
technically difficult.

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