This paper, the second of three sections of a review, deals with propionate and acetate formation, carboxylation, decarboxyiation, and transcarboxylation, the roles of biotin and vitamin B12, and the enzymes involved in the propionic-acid fermentation. Pathways for propionate, acetate, and carbon dioxide formation by Propionibacterium have been thoroughly investigated and established. These investigations led to discovery of transcarboxylase, a biotin-containing enzyme, and were the result of studies showing that the formation of propionate does not involve the expected turnover of CO2. This enzyme appears to be unique to propionibacteria; it could be speculated that it is the first discovered of a group of transcarboxylases. One of the breakthroughs relative to the mechanism of biotin fixation reactions was the discovery that biotin can be carboxylated enzymatically.

This review, appearing in three parts, is concerned with the growth, metabolism, and miscellaneous metabolic activities of propionibacteria. The first section, presented here, deals primarily with nutritional requirements, substrate and product inhibition, physical factors, associative action of other microorganisms, and enumeration and isolation of propionibacteria. The nutrition of propionic-acid bacteria has been extensively investigated and the absolute requirements for their nutrition are known. Since propionibacteria play an important role in the fermentation of Swiss cheeses, development of a completely selective medium and continued study of agents inhibitory and stimulatory to propionibacteria would be a valuable aid in solving many of the practical problems associated with Swiss cheese manufacture. Part two will discuss formation of propionate and acetate, the carboxylation, decarboxylation, and transcarboxylation reactions, the roles of biotin and vitamin B12, and the enzymes involved in the propionic-acid fermentation. The third and final section concerning miscellaneous metabolic activities will deal with erythritol metabolism, formation of diacetyl-acetoin and vitamin B12, production of previously undiscussed volatile compounds, propionin, lipids and phospholipids, and the production of slime. The third section also will include concluding comments to provide a brief summary of the important points developed in this review.

This is the third and final section of a review of the propionic-acid bacteria. This section discusses some of their miscellaneous metabolic activities such as: erythritol metabolism, formation of diacetyl-acetoin and vitamin B12, production of volatile compounds not previously mentioned, propionin (an antiviral agent), lipids and phospholipids, and slime formation, Concluding comments provide a brief summary of particular points of interest.

No abstract

No abstract