Fermentation of primary alcohols and diols and pure culture of syntrophically alcohol-oxidizing anaerobes

Ethanol, propanol, ethylene glycol, 1,2-propanediol, 1,2-butanediol, acetoin, diacetyl, and 2,3-pentanedione were used as substrates for enrichment and isolation of alcohol-oxidizing fermentative bacteria. Diacetyl and 2,3-pentanedione proved to be highly toxic. With the other substrates, various kinds of bacteria could be isolated which were assigned to three different metabolic groups: (i) homoacetogenic bacteria, and (ii) bacteria forming propionate as reduced end product were isolated from freshwater sources; (iii) bacteria disproportionating acetoin and 1,2-diols to acids and primary alcohols were isolated from marine sediments. The latter oxidized primary alcohols to fatty acids in the presence of hydrogen-oxidizing partners. Syntrophically ethanol-oxidizing cocultures enriched with primary alcohols could be separated with 1,2-diols as substrates into an alcohol-oxidizing organism and a hydrogen-oxidizing homoacetogen. The pathways of alcohol conversion in the disproportionating isolates were studied in detail. Growth experiments as well as enzymological studies demonstrated that acetoin and 1,2-diols were degraded via acetaldehyde which was also an intermediate in syntrophic oxidation of primary alcohols. The environmental importance of the various metabolic types isolated was assessed by most-probable-number enumerations.