Dissecting the taxonomic heterogeneity within Propionibacterium acnes: proposal for Propionibacterium acnes subsp acnes subsp nov and Propionibacterium acnes subsp elongatum subsp nov.

Propionibacterium acnes subsp. acnes subsp. nov. and Propionibacterium acnes subsp. elongatum subsp. nov. are described. These emanate from the three known phylotypes of P. acnes, designated types I, II and Ill. Electron microscopy confirmed the filamentous cell shape of type Ill, showing a striking difference from types I/II, which were short rods. Biochemical tests indicated that, in types I/II, either the pyruvate, L-pyrrolidonyl arylamidase or D-ribose 2 test was positive, whereas all of these were negative among type Ill strains. Matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) spectra, which profile mainly their ribosomal proteins, were different between these two groups. Surface-enhanced laser-desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS) spectra of all phylotypes revealed a specific protein biomarker that was overexpressed in type Ill strains compared with types I/II only when grown aerobically. Reference strains had high whole-genome similarity between types I (>91 %) and II (>75 %), but a considerably lower level of 72 % similarity with type Ill. recA and gyrB sequence dendrograms confirmed the distant relatedness of type III, indicating the presence of two distinct centres of variation within the species P. acnes. On the other hand, cellular fatty acid profiles and 16S rRNA gene sequence relatedness (>99.3 %) circumscribed the species. Thus, we propose two subspecies, Propionibacterium acnes subsp. acnes subsp. nov. for types I/II and Propionibacterium acnes subsp. elongatum subsp. nov. for type Ill. The type strain of Propionibacterium acnes subsp. acnes is NCTC 737(T) (=ATCC 6919(T)=JCM 6425(T)=DSM 1897(T)=CCUG 1794(T)), while the type strain of Propionibacterium acnes subsp. elongatum is K124(T) (=NCTC 13655(T)=JCM 18919(T)).