General Microbiology - Schlegel, H. 1987

Types of Fermentation
Fermentable and Non-Fermentable Natural Compounds

Most natural compounds composed of carbon, hydrogen, oxygen, and (or) nitrogen can undergo Fermentation under anaerobic conditions. A prerequisite for this is the possibility of partial substrate oxidation resulting from intramolecular Cleavage accompanied by energy release (an exergonic reaction). Examples of substances susceptible to fermentation include Polysaccharides, hexoses, pentoses, tetroses, polyhydric alcohols, organic acids (including sugar acids, gluconate, malate, tartrate, etc.), Amino Acids (except for aromatic ones, which are only conditionally fermentable), Purines, and Pyrimidines.

Alongside compounds that undergo anaerobic fermentation, there are substances incapable of being fermented. These include saturated aliphatic and aromatic Hydrocarbons, Steroids, carotenoids, Terpenes, and Porphyrins. Under aerobic conditions, all these substances undergo degradation and are completely oxidized, whereas under anaerobic conditions they remain highly stable. This stability can be attributed to two main reasons. First, most of the aforementioned compounds contain only carbon and hydrogen atoms; intramolecular cleavage of such substances yields no energy. Second, saturated hydrocarbons and polyisoprenoids can only be oxidized in the presence of molecular oxygen, with their initial breakdown catalyzed by oxygenases. The high stability of hydrocarbons under anaerobic conditions is confirmed in virtually every laboratory experiment. Apparently, it is precisely this stability that allows hydrocarbons to persist in petroleum deposits for such vast periods of time. Evidently, during the era of oil formation, microorganisms lacked The ability to ferment paraffins, nor have they acquired it to this day.

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Fig. 8.10. Summary scheme of the major fermentation pathways.