Disruptive Effects of Tris and Sodium Lauroyl Sarcosinate on the Outer Membrane of Pseudomonas cepacia Shown by Fluorescent Probes

This study investigated how Tris buffer and sodium lauroyl sarcosinate (Sarkosyl) disrupt the outer membrane (OM) of Pseudomonas cepacia using fluorescent probes. Researchers grew P. cepacia and exposed its cells and isolated outer membranes to various fluorescent dyes including ANS, TNS, and CC5. Tris buffer significantly increased OM permeability to fluorescent probes, with effects enhanced at lower pH values. In contrast, MOPS buffer showed only minor effects at acidic pH, while citrate/phosphate buffer had negligible impact. Sarkosyl, a detergent commonly used in OM preparation, released the fluorescent marker CC5 from both isolated OM and whole cells, indicating it penetrates and disrupts the membrane structure. Sarkosyl treatment also altered OM fluidity, increasing fluorescence polarization approximately twofold and raising membrane microviscosity by about 0.5 poise. The authors concluded that Tris damages the OM likely by disrupting salt bridges between divalent cations and membrane components like lipopolysaccharide. They cautioned that Sarkosyl should not be used when studying OM physical properties and may remove OM proteins, requiring careful interpretation of results.

Key findings

• Tris buffer disrupts the outer membrane of P. cepacia by increasing permeability to fluorescent probes, with effects enhanced at lower pH
• MOPS buffer shows minor OM disruption at acidic pH, while citrate/phosphate buffer has negligible effects
• Sarkosyl detergent removes fluorescent markers from outer membranes and whole cells, indicating direct membrane disruption
• Sarkosyl treatment increases outer membrane microviscosity and reduces membrane fluidity by approximately twofold
• Tris likely disrupts salt bridges between divalent cations and lipopolysaccharide in the outer membrane