Summary: A mutant of which grew in complex medium at 30 °C but lysed at 45 °C has been isolated. It could only grow on minimal medium at 45 °C with added aspartate (20 μg ml) but lysed if lysine (20 μg ml) was also present. The requirement for aspartate was due to a low activity of pyruvate carboxylase; the site of the mutation () was linked (16% cotransducible using phage PBSI) to the This defect appeared to lead to decreased synthesis of -diaminopimelic acid (Apm), an amino acid unique to peptidoglycan and its precursors. At the restrictive temperature the mutant accumulated uridine-5′-diphosphate -acetylmura-myl-l-alanyl-d-glutamate, since Apm is the next amino acid to be added to the growing peptide chain of peptidoglycan. This resulted in an inhibition of peptidoglycan synthesis, determined as a reduced incorporation of -acetyl[C]glucosamine. Peptidoglycan synthesis was not decreased if the mutant was grown in media containing aspartate but lacking lysine.

The sensitivity to lysine may arise because (i) at 45 °C the mutant was starved for aspartate and hence Apm even when aspartate was present, since aspartate utilization, as estimated by the incorporation of [H]aspartate into trichloroacetic acid precipitable material, was relatively inefficient; and (ii) this diminished level of Apm synthesis from aspartate was further curtailed since lysine inhibits one of the aspartokinases in Thus, addition of lysine allowed protein synthesis and hence autolysin production to proceed whilst peptidoglycan synthesis remained inhibited.

When autolysis was blocked, either indirectly by stopping protein synthesis through starvation of aspartate lysine, or directly by introducing a mutation, then shifting the mutant to 45 °C did not result in lysis but growth still ceased.


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