A New Type of Glucose Fermentation by Clostridium thermoaceticum
The thermophilic fermentation of cellulosic material is generally regarded -as a result of the combined action of several species of bacteria, some of which attack the cellulose and others the sugars formed from the breakdown of the cellulose. Much effort has been spent on attempts to isolate the cellulose fermenters but very little attention has been paid to the associated sugar-fermenting organisms. Snieszko and Kimball (1933) isolated and described two types of such bacteria but gave no chemical data on the fermentation products formed. It, therefore, seemed desirable to make such a study.
Methane formation from fructose by syntrophic associations of Acetobacterium woodii and different strains of methanogens
When Acetobacterium woodii was co-cultured in continuous or in stationary culture with Methanobacterium strain AZ, fructose instead of being converted to 3 mol of acetate was converted to 2 mol of acetate and 1 mol each of carbon dioxide and methane, showing that interspecies hydrogen transfer occurred. In continous culture the organisms formed a close physical association in clumps; the doubling time for each organism was 6h at 33°C. Methane mainly was derived from carbon positions 3 and 4 of the sugar, but other carbons also yielded methane; this was shown to be due to carbon dioxide-acetate exchange reactions by A. woodii in a manner similar to that carried out by Clostridium thermoaceticum. Four other methanogens, Methanobacterium M.o.H. and M.o.H. G, Methanobacterium formicicum, and Methanosarcina barkeri (not acetate-adapted) also produced similar results, when co-cultured with A. woodii.
OXIDATION AND REDUCTION RELATIONS BETWEEN SUBSTRATE AND PRODUCTS IN THE ACETONEBUTYL ALCOHOL FERMENTATION
The anaerobic fermentation of a carbohydrate or related compound is primarily a process of oxidation and reduction. All products of sugar fermentation are formed by a series of intermolecuIar and intramolecular oxidations and reductions, with att’endant coupling and splitting reactions. Complex as these rearrangements may be, there are certain quantitative relationships which must always hold true. If the fermentation is anaerobic, oxidation of one compound must be accompanied by reduction of another compound. The various oxidized and reduced fermentation products therefore, must always be present in a ratio such that the degree of oxidation of the system as a whole remains constant. This relationship, is, of course, entirely independent of the fermentative mechanism. The following is a convenient method of calculating such an oxidation-reduction balance. Let us take as a standard of the degree of oxidation a compound in which hydrogen and oxygen are present in equivalent proportions, that is, in the ratio to form water. Examples of such compounds are glucose (C$H,,Os), methyl glyoxal (C&LO,), and acetic acid (GH402). Then we may evaluate other compounds according to the number of hydrogen atoms they contain in excess of the number necessary to combine with the oxygen present in the molecule. Thus acetaldehyde (C2H40) has a reduction value of fl, since it contains 2 atoms of hydrogen more than is needed to combine wit,h the