New insights about phenotypic heterogeneity within Propionibacterium freudenreichii argue against its division into subspecies

Abstract

Propionibacterium freudenreichii is widely used in Swiss-type cheese manufacture, where it contributes to flavour and eye development. It is currently divided into two subspecies, according to the phenotype for lactose fermentation and nitrate reduction (lac+/nit− and lac−/nit+ for P. freudenreichii subsp. shermanii and subsp. freudenreichii, respectively). However, the existence of unclassifiable strains (lac+/nit+ and lac−/nit−) has also been reported. The aim of this study was to revisit the relevance of the subdivision of P. freudenreichii into subspecies, by confirming the existence of unclassifiable strains. Relevant conditions to test the ability of P. freudenreichii for lactose fermentation and nitrate reduction were first determined, by using 10 sequenced strains, in which the presence or absence of the lactose and nitrate genomic islands were known. We also determined whether the subdivision based on lac/nit phenotype was related to other phenotypic properties of interest in cheese manufacture, in this case, the production of aroma compounds, analysed by gas chromatography-mass spectrometry, for a total of 28 strains. The results showed that a too short incubation time can lead to false negative for lactose fermentation and nitrate reduction. They confirmed the existence of four lac/nit phenotypes instead of the two expected, thus leading to 13 unclassifiable strains out of the 28 characterized (7 lac+/nit+ and 6 lac−/nit−). The production of the 15 aroma compounds detected in all cultures varied more within a lac/nit phenotype (up to 20 times) than between them. Taken together, these results demonstrate that the division of P. freudenreichii into two subspecies does not appear to be relevant.

Strain-to-strain differences within lactic and propionic acid bacteria species strongly impact the properties of cheese–A review

“…The formation of many other amino acid-derived aroma compounds varied significantly depending on the PAB strain, in P. freudenreichii as well as in the three other dairy PAB species (Yee et al 2014). The ability to produce aroma compounds was not correlated with the subspecies of P. freudenreichii (De Freitas et al 2015). The mechanism responsible for this strain-dependency is still unknown.…”

Mihaliç Peynirlerinden İzole Edilen Propionibacterium Türlerinin MALDI-TOF MS ile Tanımlanması

“…shermanii was second highest (33%) propionic acid bacteria found in cheese samples. It has been difficult to distinguish between the subspecies in identification by conventional methods since P. freudenreichii subspecies freudenreichii and shermanii can be differentiated by lactose fermentation and nitrate reduction, while shermanii can ferment lactose and not have reductase activity for nitrate (De Freitas et al, 2015). Although molecular methods have failed up to separate P. freudenreichii subspecies, MALDI-TOF analysis has been successful method for characterization of intraspecific differences (subspecies, strains) (Vorob'eva et al, 2011).…”

Propionibacteria as promising tools for the production of pro-bioactive scotta: a proof-of-concept study

“…Microplates were incubated under anaerobic conditions (Anaerocult A system, Merck, Darmstadt, Germany) for 7 days at 30°C. The production of acid from lactose was determined based on bromocresol purple color change ( de Freitas et al, 2015 ). For the evaluation of the kinetics of growth on lactose, cells were inoculated to a final OD 650 = 0.01 in 200 μL YELactose within 96 well microplates.…”