Protective effect of sucrose and sodium chloride for Lactococcus lactis during sublethal and lethal high-pressure treatments

• Published in: Applied and Environmental Microbiology 2004-04, Vol.70 (4), p.2013-2020
• Main Authors: Molina-Hoppner, A, Doster, W, Vogel, R.F, Ganzle, M.G
• Format: Article
• Language: English
• Subjects: antibacterial properties; Bacteria; Bacterial Proteins - metabolism; baroprotective effect; Biological and medical sciences; Buffers; cell membranes; cytochemistry; Drug resistance; Drug Resistance, Multiple, Bacterial; Food Microbiology; food processing; Fundamental and applied biological sciences. Psychology; high pressure treatment; hydrogen ions; Hydrogen-Ion Concentration; Hydrostatic Pressure; intracellular pH; ion transport; Kinetics; Lactococcus lactis; Lactococcus lactis - drug effects; Lactococcus lactis - metabolism; Lactococcus lactis subsp. cremoris; lactose; membrane fluidity; Membrane Fluidity - drug effects; Membrane Transport Proteins - metabolism; Microbiology; Pressure; protective effect; sodium chloride; Sodium Chloride - pharmacology; Spectroscopy, Fourier Transform Infrared; sucrose; Sucrose - pharmacology; Temperature
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.70.4.2013-2020.2004

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 (deltapH), 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 deltapH 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.