Protective Effect of Sucrose and Sodium Chloride for Lactococcus lactis during Sublethal and Lethal High-Pressure Treatments

Abstract

The bactericidal effect of hydrostatic pressure is reduced when bacteria are suspended in media with high osmolarity. To elucidate mechanisms responsible for the baroprotective effect of ionic and nonionic solutes, Lactococcus lactis was treated with pressures ranging from 200 to 600 MPa in a low-osmolarity buffer or with buffer containing 0.5 M sucrose or 4 M NaCl. Pressure-treated cells were characterized in order to determine viability, the transmembrane difference in pH (⌬pH), and multiple-drug-resistance (MDR) transport activity. Furthermore, pressure effects on the intracellular pH and the fluidity of the membrane were determined during pressure treatment. In the presence of external sucrose and NaCl, high intracellular levels of sucrose and lactose, respectively, were accumulated by L. lactis; 4 M NaCl and, to a lesser extent, 0.5 M sucrose provided protection against pressure-induced cell death. The transmembrane ⌬pH was reversibly dissipated during pressure treatment in any buffer system. Sucrose but not NaCl prevented the irreversible inactivation of enzymes involved in pH homeostasis and MDR transport activity. In the presence 0.5 M sucrose or 4 M NaCl, the fluidity of the cytoplasmic membrane was maintained even at low temperatures and high pressure. These results indicate that disaccharides protect microorganisms against pressure-induced inactivation of vital cellular components. The protective effect of ionic solutes relies on the intracellular accumulation of compatible solutes as a response to the osmotic stress. Thus, ionic solutes provide only asymmetric protection, and baroprotection with ionic solutes requires higher concentrations of the osmolytes than of disaccharides.The accumulation of compatible solutes, such as betaines, proline, and sugars, is a widespread response of microorganisms to elevated environmental osmotic pressures (41). According to a recent definition, a compatible solute is a "cytoplasmic cosolvent (solute) whose levels can be modulated over a broad range without disrupting cellular function" (24, 43). Compatible solutes contribute to the osmotic balance with the extracellular environment, enhance the stability of enzymes, and preserve the integrity of biological membranes (41). The composition of the osmolytes that are accumulated depends on the type of osmotic shock (i.e., ionic stress versus nonionic stress) and the presence of specific compatible solutes in the medium. In addition to their role as osmotic balancers, compatible solutes provide protection against high temperature, freeze-thaw treatment, and drying (41, 43).When the osmotic pressure of the medium is increased, the tolerance of microorganisms to high hydrostatic pressure is enhanced. Baroprotective effects of sodium chloride or sugars have been observed in studies with Escherichia coli, Saccharomyces cerevisiae, Zygosaccharomyces spp., and Rhodoturula rubra (14,17,24,25,36). The influence of salts or sugars on the water activity (a w ) of foods or suspension media does not explain the marked baroprotectiv...

Stress Physiology of Lactic Acid Bacteria

“…Other osmotically active compounds, such as the disaccharide sucrose, protect Lc. lactis cells against pressure-induced inactivation of vital cellular components (279). The protective effect of ionic solutes has been ascribed to the intracellular accumulation of compatible solutes as a response to osmotic stress.…”

Solutes determine the temperature windows for microbial survival and growth

“…(i) High-temperature treatment exacerbates the lethality of high pressures for microbial spores (27). (ii) Sucrose and NaCl (both kosmotropic) protect Lactococcus lactis against potentially lethal high-pressure treatments (28). (iii) Low temperatures enhance pressure tolerance of stationary phase E. coli cells (29).…”

Exploration of the Effects of High Hydrostatic Pressure on Microbial Growth, Physiology and Survival: Perspectives from Piezophysiology

“…41) High concentrations of sucrose have a protective effect against lethal levels of hydrostatic pressure in E. coli 42) and Lactococcus lactis (piezotolerance). 43,44) Piezotolerance is inducible in Lactococcus sanfranciscensis by preincubation under hydrostatic pressure, cold or osmotic shock, and acidity. 45) Spores of Bacillus species are germinated by a variety of stimuli including nutrients, some chemicals and mechanical treatments such as abrasion and high pressure.…”