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The amino acid composition of isolated cell walls of Bacillus psychrophilushas been determined before and after extraction of protein with ethylenediamine-tetraacetic acid at 45 C. This revealed that the peptidoglycan consists of Ala, Lys, and Glu in a molar ratio of 3:1:2. By using autolytic digests of log-phase cell walls, it was possible to detect 14 ninhydrin-positive degradation products. Chemical analyses of the seven major bands from these digests indicated that the amino acid sequence of the peptide subunit in the murein of this organism consists of muramyl-l-alanyl-γ-d-glutamyl-l-lysyl- d-alanine, and the linkage between adjacent peptides is supplied by a second d-glutamic acid which is bound to the σ-amino group of lysine and the carboxyl group of the d-alanine through its amino group. The nature of the solubilized wall fragments indicates that each of the peptide bonds in the murein is hydrolyzed by autolysins except the l-alanyl-γ-d-glutamyl linkage.

Cell walls isolated from Bacillus psychrophilusautolyse at temperatures which support growth. At temperatures above the maximum growth temperature (28 C), a nonenzymatic lysis occurs. Removal of autolytic enzyme activity with 10 mLiCl had little effect on the rate or extent of lysis at elevated temperatures (37 and 45 C). Nonenzymatic lysis was characterized chemically by a decrease in the liberation of N-terminal groups, and the effects of pH, Ca2+, and ethylenediaminetetraacetic acid suggest that ionic linkages are involved in much of the integrity of the cell wall of this psychrophile. The nonenzymatic absorbance decrease at 45 C can be reversed to the extent of 70 to 100% at 0 C. Centrifugation of a heat-lysed wall suspension separated a soluble protein component which is required for low-temperature reaggregation. Preliminary evidence indicates the insoluble residue which remains after temperature-mediated lysis is primarily peptidoglycan.