Isolation of aminopeptidase N genes of food associated propionibacteria and observation of their transcription in skim milk and acid whey.

In this study consensus oligonucleotides PN5/PN3 were designed by aligning the aminopeptidase N genes (pep N) of various actinobacteria and applied to the isolation of the pep N genes of dairy propionibacteria (PAB) and closely related species associated with food. This allowed sequencing of a pep N gene region from Propionibacterium jensenii LMG 16541. The sequence of this gene was completed by inverse PCR. Consensus primer pairs NU1/D1 and NU2/D1 were derived from the alignment of the new sequence with its homologues in Propionibacterium acnes and other actinobacteria; these were used to start sequencing of the pep N genes of Propionibacterium freudenreichii, Propionibacterium thoenii, Propionibacterium microaerophilum, Propionibacterium acidipropionici, Propioni bacterium cyclohexanicum and Propionibacterium microaerophilum. Reverse transcription coupled with PN5/PN3 and NU1/D1 PCR tests indicated that the pep N genes of P. jensenii and P. freudenreichii are expressed during growth in skim milk and acid whey.