BACTERIAL FERMENTATIONS 



from various organic and inorganic compounds; the latter 

 oxidize methane to carbon dioxide and water. 



Enrichment and Isolation. The methane bacteria have 

 not been studied as extensively as most other groups of 

 bacteria of comparable scientific and practical importance. 

 The reason for this is readily apparent. In order to study 

 the biology and biochemistry of bacteria most effectively, 

 it is necessary to use pure cultures, that is, to study one 

 species at a time. Unfortunately, with the methane bac- 

 teria, this elementary but basic requirement has been diffi- 

 cult and in many instances impossible to achieve. 



Until 1936 all attempts to isolate pure cultures, or even 

 to obtain growth of colonies in solid media, were unsuc- 

 cessful. 7 Consequently all the early studies and many of 

 the more recent studies of methane bacteria were of neces- 

 sity carried out with enrichment cultures, i.e., cultures in 

 which the substrate and environmental conditions were 

 chosen in such a way as to favor the development of certain 

 species of methane bacteria, without, however, excluding 

 a substantial and frequently significant number of other 

 bacterial species, both methane-producing and non-produc- 

 ing types. By the use of enrichment cultures it was possible 

 to obtain considerable information about the existing mor- 

 phological types of methane bacteria, the general environ- 

 mental conditions that favor their development, the kinds 

 of substrates attacked and the over-all chemical reactions 

 involved, but many basic points of biology, nutrition, and 

 biochemistry could not be studied effectively with these 

 cultures. 



Since 1936 four species of methane bacteria (Metha- 

 nobacillus omelianskii/ Methanobacterium formicicum* 

 Methanosarcina barkerii, 9 Methanococcus vannielii 10 ) be- 

 longing in three different genera have been isolated in 

 pure culture. An additional four species (Mbact. suboxy- 



