Classification of propionic acid bacteria and approaches to applied genetics

Abstract

Strains of the genus Propionibacterium, which were recently classified within the new class Actinobacteria, are grouped into cutaneous (medical) or dairy (classical) propionic acid bacteria. 16S rDNA sequences of all Propionibacterium 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 distinct from both the closely related clusters of P. freudenreichii and P. cyclohexanicum. Within the cutaneous species, three groups were clustered: P. granulosum forms a distinct cluster between the classical groups and a group containing P. avidum, P. acnes and P. propionicum, whereas P. lymphophilum is placed more distantly from any group in this tree. In order to differentiate Propionibacterium isolates from other food-isolates a rapid multiplex-PCR (MPCR) method based on 16S rRNA-targeted oligonucleotides and particularly on a 16S rDNA-motif which turned out to be specific for the genus Propionibacterium was developed. The MPCR-amplification could be performed within 1 d and reached detection limits of 103 colony forming units or 35 pg of DNA. The MPCR-method was used in various Propionibacterium screening studies. 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 SM1 and cloning of its genetic locus is currently under way. © Inra/Elsevier, Paris.