Ultrastructural localization of the maltose-binding protein within the cell envelope of Escherichia coli.

Logarithmically growing cells of Escherichia coli were fixed with glutaraldehyde and incubated with antimaltose-binding protein Fab coupled to horseradish peroxide (molecular weight of the complex 80,000). The position of this complex within the cell envelope was determined by reacting with diaminobenzidine-H2O2, staining with osmium tetroxide and processing for thin section electron microscopy. The following observations were made: (i) induction of the maltose-binding protein resulted in swelling and staining of the outer membrane; (ii) the swelling and staining was more prominent in short cells, less prominent or absent in long cells; (iii) rare examples exhibited granular staining in the space between the plasma membrane and the peptidoglycan layer. These stainings were observable mainly in pole caps; (iv) a mutant lacking the receptor for phage lambda showed altered staining pattern. Treatment of glutaraldehyde-fixed cells with EDTA-lysozyme prevented the specific labelling of the maltose-binding protein.