THE GENUS PROPIONIBACTERIUM

Bacteria from the genera Lactobacillus and Streptococcus are involved in the first steps of dairy production (3). The raw materials produced by their effects usually only acquire their final properties after additional fermentation processes. For example, the characteristic taste of Swiss cheese develops during a subsequent propionic acid fermentation. In this process, bacteria from the genus Propionibacterium convert pyruvate to propionate in a complex series of reactions (2). 

Hargrove and Leviton (1955) and Leviton (1956A,B) found that bacteria in the genus Propionibacterium elaborated vitamin Bi2-active substances in concentrations equal to or greater than those reportedly obtained with other organisms. The active compound produced was identified as hydroxocobalamine. 

Anaerobic corynebacteria are also included in the genus Propionibacterium after the pioneering studies of Douglas and Gunter (1946). They were transferred from the genus Corynebacterium since they are ... 

The most important property of the genus Propionibacterium is the production of propionic acid as a result of the propionic acid fermentation dependent on coenzyme B12. If the dependence on coenzyme Bn is disregarded, some clostridial strains that do not form spores may be erroneously attributed as propionibacteria. For example, Cl botulinum, Cl propionicum and some other species can produce propionic acid, but propionibacteria have the GC-type DNA (65-67 mol% G+C in classical and 53-62 mol% in cutaneous bacteria), while clostridial DNA is of the AT-type (25-30 mol% G+C). 

All propionic acid bacteria are catalase-positive P. arabinosum displays a very weak catalase activity). As a rule, members of the genus Propionibacterium produce significant amoxmts of vitamin Bn. We (Vorobjeva, 1976) suggested to differentiate propionibacteria by the nature of the coenzyme form of vitamin Bn. The presence of the isomerization reaction of succinyl-CoA methylmalonyl-CoA, which is the key reaction of propionic acid fermentation, represents another valuable taxonomic property of the genus. 

Still, P. coccoides is not included in Bergey s Manual of Determinative Bacteriology (1994), despite its recognition by Cummins and Johnson (1992) as a probable member of the genus Propionibacterium. 

Figure 1.24. Phylogenetic tree of the genus Propionibacterium based on 16S rDNA sequences. Reproduced from Dasen et al. (1998), with permission.

Propionic acid bacteria represent a distinct and ancient evolutionary branch ascending from an actinomycetous ancestor. It is a bridge that links the past and present. Three subgroups of propionic acid bacteria classical, cutaneous, and P. propionicum comprise the genus Propionibacterium, The classical propionibacteria inhabit mainly milk and cheese (hence their second name—dairy propionic acid bacteria), the cutaneous species inhabit human skin and the rumen of ruminants, and P. propionicum dwells in the soil. 

Charfreitag O and Stackebrandt E (1989) Inter- and intrageneiic relationships of the genus Propionibacterium as determined by 16S rRNA sequences. J Gen Microbiol 135 2065-2070... 

Delwiche EA (1949) Vitamin requirements in the genus Propionibacterium. J Bacteriol 58 395-398... 

Joseph AA and Wixom RL (1972) Amino acid metabolism in the genus Propionibacterium. Proc Soc Exp Biol Med 139 526-534... 

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