Resolution of Bacterial Proteins by Polyacrylamide Gel Electrophoresis on Slabs

The application of a method of electrophoretic protein analysis to the investigation of the total protein composition of Salmonella typhimurium is described. It involves electrophoresis of many samples simultaneously on a thin slab of acrylamide gel, in the presence of sodium dodecyl sulfate, with the discontinuous buffer system of Laemmli ((1970) Nature 227, 680–685). Up to about 25 samples can be run simultaneously, thus improving both efficiency and ability to compare patterns. The sensitivity of the method for detection of changes both in soluble proteins and the insoluble membrane proteins of the cell is shown. Membrane preparations from the wild type strain and many different mutant strains have been analyzed. The major membrane proteins observed and their relationship to proteins described in the literature are discussed. The marked changes detected in a variety of mutant strains and under a variety of growth conditions are also discussed, either as to their specific meaning or as evidence of the effectiveness of the method. Solubilization artifacts concerning the proteins of the outer cell membrane are presented. The membrane fractions from two Escherichia coli strains have also been analyzed.