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Modification of the silver staining technique to detect lipopolysaccharide in polyacrylamide gels
A Fomsgaard1, M A Freudenberg, C Galanos
1Max-Planck Institut für Immunbiologie, Freiburg, Federal Republic of Germany.
Abstract:
A silver staining method used routinely for detecting bacterial lipopolysaccharide (LPS) in sodium dodecyl sulfate-polyacrylamide gels (C. Tsai and E. Frasch, Anal. Biochem. 119:115-119, 1982) appeared to be inappropriate for visualizing certain LPS preparations. It did not stain S-form fractions of polyagglutinable Pseudomonas aeruginosa LPS or several partly deacylated (alkali-treated) S-form LPS after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. However, these LPS preparations could be detected by anti-LPS sera after electroblotting onto nitrocellulose, thereby confirming their integrity and presence in the polyacrylamide gel. This is because LPS fractions containing a low number of fatty acids are washed out of the gel during the initial fixing step (40% ethanol-4% acetic acid, overnight). By omitting this fixing step, which was originally developed for detecting proteins, and by increasing the LPS oxidation time (from 5 to 20 min), we restored the ability to detect LPS fractions that otherwise would not be stained. These modifications did not affect the detection of other S- and R-form LPSs. Thus, differences in the number of fatty acids present in polyagglutinable P. aeruginosa LPS may result in a selective loss of fatty acid-deficient S-form LPS in these apparent R-form LPS preparations. This modified procedure provides a fast, simple, and sensitive way to analyze LPS in polyacrylamide gels despite the number of acyl groups present.
Insights
A modified silver staining method enhances the detection of bacterial lipopolysaccharide (LPS) in polyacrylamide gels, even for preparations with low fatty acid content. This improved technique ensures accurate visualization of all LPS forms, aiding bacterial analysis.
Area of Science:
- Microbiology
- Biochemistry
- Analytical Chemistry
Background:
- Standard silver staining methods for bacterial lipopolysaccharide (LPS) in polyacrylamide gels are unsuitable for certain LPS types.
- Partly deacylated or S-form Pseudomonas aeruginosa LPS fractions are not visualized by routine silver staining.
- These LPS preparations are detectable by anti-LPS sera after electroblotting, indicating integrity but poor staining.
Purpose of the Study:
- To develop a modified silver staining protocol for improved visualization of bacterial lipopolysaccharide (LPS) in polyacrylamide gels.
- To address the issue of selective loss of fatty acid-deficient LPS during standard staining procedures.
- To ensure accurate detection of all LPS forms, including those with varying fatty acid content.
Main Methods:
- Modified the standard silver staining protocol by omitting the ethanol-acetic acid fixing step.
- Increased the LPS oxidation time from 5 to 20 minutes.
- Compared the modified method with standard protocols for visualizing various LPS preparations, including S-form and R-form LPS from Pseudomonas aeruginosa.
Main Results:
- The modified silver staining method successfully visualized LPS fractions that were previously undetectable, including alkali-treated and S-form Pseudomonas aeruginosa LPS.
- Omitting the fixing step prevented the washout of LPS with low fatty acid content.
- The modifications did not interfere with the staining of other S- and R-form LPS, demonstrating broad applicability.
Conclusions:
- The modified silver staining procedure is a fast, simple, and sensitive method for analyzing bacterial lipopolysaccharide (LPS) in polyacrylamide gels.
- Differences in fatty acid content can lead to selective loss of LPS during standard staining; the modified method overcomes this limitation.
- This technique allows for accurate assessment of LPS integrity and presence, regardless of acyl group variations.