Classification of propionic acid bacteria and approaches to applied genetics

Strains of the genus Propionibacterium, which were recently classified with in the new class Actinobacteria, are grouped into cutaneous (medical) or da iry (classical) propionic acid bacteria. 16S rDNA sequences of all Propioni bacterium type strains and some new isolates were completed. A phylogenetic tree was constructed and current trees reexamined. The classical species P . thoenii, P. jensenii and P. acidipropionici were clustered in a group dis tinct from both the closely related clusters of P, freudenreichii and P. cy clohexanicum. Within the cutaneous species, three groups were clustered: P. granulosum forms a distinct cluster between the classical groups and a gro up containing P. avidum, P. acnes and P. propionicum, whereas P. lymphophil um is placed more distantly from any group in this tree. In order to differ entiate Propionibacterium isolates from other food-isolates a rapid multipl ex-PCR (MPCR) method based on 16S rRNA-targeted oligonucleotides and partic ularly on a 16S rDNA-motif which turned out to be specific for the genus Pr opionibacterium was developed. The MPCR-amplification could be performed wi thin 1 d and reached detection limits of 10(3) colony forming units or 35 p g of DNA. The MPCR-method was used in various Propionibacterium screening s tudies. In the course of screening antifungal and antibacterial activities of propionic acid bacteria, a Propionibacterium jensenii strain containing a cryptic 7-kb plasmid was identified. This strain produced the bacteriocin Propionicin SM1. Purification of Propionicin SM 1 and cloning of its genet ic locus is currently under way. (C) Inra/Elsevier, Paris.