Stress and osmoprotection in propionibacteria

Abstract

Propionibacterium starters are subjected to many stresses during Swiss-type cheese manufacture. Among the phenomena which exert strong effects on Propionibacterium growth, osmotic stress influences the cell activity, the spatial cell distribution in the loaf and also drastically influences cheese ripening. In a chemically defined medium (M63), the generation time of Propionibacterium freudenreichii subsp. shermanii CIP 103027 was doubled by 0.3 mol·L-1 sodium chloride and at 0.7 mol·L-1, growth was almost totally inhibited. Growth in rich medium was more resistant to hyperosmotic conditions. 13C Nuclear magnetic resonance (NMR) spectroscopy was used to investigate the intracellular solute pools in living cell suspensions and in hydroalcoholic extracts. Glutamate and trehalose were the main osmolytes found in the intracellular fraction of the cells in M63 containing 0.5 mol·L-1 NaCl. Addition of glycine-betaine, dimethylsulfoniopropionate or dimethyl-sulfonioacetate to this medium partially restored the growth. These efficient osmoprotectors were accumulated by the stressed cells. Moreover, glutamate and trehalose synthesis were also enhanced. In a rich medium, P. shermanii cells responded to changes in osmolarity by increasing the concentrations of specific solutes, and especially glycine-betaine, in order to maintain a constant turgor pressure. Implications of such behavior in cheese technology are discussed. © Inra/Elsevier, Paris.