Benefits and drawbacks of osmotic adjustment in Propionibacterium freudenreichii

Abstract

Propionibacterium freudenreichii is a beneficial bacterium used as a cheese starter and as a probiotic. Indeed, selected strains of P. freudenreichii combine both technological and health-promoting abilities. Moreover, during large-scale industrial production of dried bacteria and during consumption, P. freudenreichii may undergo different stressful processes. Osmotic adaptation was shown to enhance P. freudenreichii tolerance towards stresses, which are encountered during freeze-drying and during digestion. In this report, we compared the osmoadaptation molecular mechanisms of two P. freudenreichii strains. Both osmotolerance and osmoadaptation were strain-dependent and had different effects on multiple stress tolerance, depending on the presence of osmoprotectants. Availability of glycine betaine (GB) restored the growth of one of the two strains. In this strain, osmotic preadaptation enhanced heat, oxidative and acid stresses tolerance, as well as survival upon freezedrying. However, addition of GB in the medium had deleterious effects on stress tolerance, while restoring optimal growth under hyperosmotic constraint. In the other strain, neither salt nor GB enhanced stress tolerance, which was constitutively low. Accordingly, whole cell proteomics revealed that mechanisms triggered by salt in the presence and in the absence of GB are different between strains. Osmotic adjustment may thus have deleterious effects on industrial abilities of P. freudenreichii. Biological significance: Propionibacteria are found in various niches including fodder, silage, rumen, milk and cheeses. This means adaptation towards different ecological environments with different physicochemical parameters. Propionibacterium freudenreichii, in particular, is furthermore used both as dairy starter and as probiotic and is thus submitted to high scale industrial production. Production and subsequent stabilization still need optimization. Drying processes like freeze-drying are stressful. Osmotic adjustments may modulated tolerance towards drying. However, they are strain-dependent, medium-dependent and may either reduce or increase stress tolerance. A case-by-case study, for each strain-medium thus seems necessary. In this work, we identify key proteins involved in osmoadaptation and give new insights into adaptation mechanisms in P. freudenreichii. This opens new perspectives for the selections of strains and for the choice of the growth medium composition. Union) status [1,2]. P. freudenreichii is consumed in high amounts, mainly in Swiss-type cheeses, but also in functional probiotic food supplements. Probiotics are "live microorganisms that, when administered in adequate amounts, confer a health benefit on the host" [3]. Modification of the life style, including Western diet (which is high in

Intracellular osmoprotectant concentrations determine Propionibacterium freudenreichii survival during drying

“…The accumulated osmoprotectants were analyzed by NMR as described by Behrends et al (2011), Pleitner et al (2012, Vaidya et al (2018), and Weinisch et al (2019). During osmoadaptation, P. freudenreichii is able to accumulate glycine betaine, trehalose, and glutamate, as already reported (Huang et al 2016c;Gaucher et al 2019). Glycine betaine is an osmoprotectant which can be accumulated by numerous bacteria such as P. freudenreichii, Lactococcus lactis, and L. plantarum (Glaasker et al 1996;Romeo et al 2003;Huang et al 2016c).…”

“…During the exponential phase (OD = 0.8), cells were harvested by centrifugation (8000g, 10 min, 30°C). Osmoprotectants were then extracted as previously described (Gaucher et al 2019). Cells were washed twice in a NaCl solution with the same osmolality as the culture medium.…”

“…Growth of P. freudenreichii in such medium triggered complex and diverse modifications within propionibacteria including changes in morphology; overexpression of stress proteins including ClpB, SodM, EF-Tu, and Hsp20; and accumulation of storage compounds including glycogen and polyphosphate (Huang et al 2016c). During osmoadaptation, P. freudenreichii is able to accumulate trehalose, glycine betaine, and glutamate (Gaucher et al 2019). Trehalose accumulation has already been reported to protect bacteria during freeze-drying (Termont et al 2006) and glycine betaine accumulation can have a positive or negative impact on drying depending on the bacterial species (Saarela et al 2005;Sheehan et al 2006;Bergenholtz et al 2012).…”

Propionibacterium freudenreichii CIRM-BIA 129 Osmoadaptation Coupled to Acid-Adaptation Increases Its Viability During Freeze-Drying

“…Cross-protections provided by adaptation are generally strain-dependent (Gaucher et al, 2019b). In a previous study, osmoadaptation exerted a positive impact on P. freudenreichii CIRM-BIA 129 viability during freeze-drying, but not during different challenges such as heat, acid or bile salts stresses (Gaucher et al, 2019a). Concerning P. freudenreichii freeze-drying, almost nothing has been published.…”

“…General stress protein like Clps, DnaK, GroES or GroEL are overproduced during these three adaptations (Jan et al, 2001; Leverrier et al, 2004; Savijoki et al, 2005; Dalmasso et al, 2012; Huang et al, 2016a). During osmoadaptation, P. freudenreichii is able to accumulate glutamate, trehalose and glycine betaine (Gaucher et al, 2019a). In hyperosmotic media, bacteria need to accumulate compatible solutes in order to preserve their turgescent pressure and to enable cell growth and division.…”