Cell Wall and Peptidoglycan from Lactobacillus fermenti

Abstract

Cell walls from Lactobacillus fermenti were prepared by differential centrifugation of disrupted cells, with and without trypsin treatment. Approximately 16% of the dry weight of walls was found in a crude trichloroacetic acid extract of the walls; half of this amount remained upon further purification. The purufied extract lacked alanine, but contained substantial amounts of glucosamine. The walls constituted 23 to 33% of the dry weight of the cell. The chemical composition of the various types of wall preparations and of the peptidoglycan from them was studied. The peptidoglycan contained equimolar proportions of glucosamine, muramic acid, l -alanine, d -glutamic acid, and lysine, with somewhat lower proportions of d -aspartic acid and d -alanine. The chemical composition of the peptidoglycan is similar to that reported for three other lactobacilli. In addition to the major constituents of walls and peptidoglycan, there were several minor amino acids. The protein and the amounts of the minor amino acids decreased, and among these threonine and arginine were completely absent from preparations obtained with trypsin. Such preparations contained higher proportions of the d -isomers of alanine, glutamic acid, and aspartic acid as compared to walls and peptidoglycan prepared without trypsin. In addition, walls isolated with the use of trypsin were susceptible to lysozyme, whereas those prepared without trypsin were not. However, the trypsin treatment did not result in any change of the ultrastructure as revealed by electron microscope studies.