GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

14. TYPES OF FERMENTATION

14.4. PROPIONIC ACID FERMENTATION AND PROPIONIC ACID BACTERIA

14.4.1. Characteristics of propionic acid bacteria

These Bacteria inhabit the rumen and intestines of ruminants (such as cows and sheep), where they participate in The production of Fatty acids, predominantly propionic and acetic acids. Through the action of these bacteria, lactic acid—produced via various Fermentation pathways—is converted into propionic acid. Propionic acid bacteria are not found in milk, soil, or aquatic environments. The genus Propionibacterium consists of Gram-positive, non-motile, non-spore-forming rods. These bacteria are intolerant to oxygen, grow under anaerobic conditions, and regenerate ATP via fermentation. Based on these traits, they were long considered obligate anaerobes. However, Enzymes such as catalase and Cytochromes were later discovered in them. It was subsequently established that members of the genus Propionibacterium are capable of growing under aerobic conditions (with mild aeration), although oxygen remains toxic to them. Thus, with respect to oxygen, propionic acid bacteria are microaerotolerant organisms. In addition to the genus Propionibacterium, propionic acid bacteria include Veillonella alcalescens, Clostridium propionicum, and Representatives of the genera Selenomonas and Micromonospora. Under anaerobic conditions, these bacteria ferment sucrose, glucose, lactose, pentoses, as well as malate, lactate, glycerol, and other substrates with the Formation of propionic acid. The breakdown of hexoses occurs via The Glycolytic Pathway.