Effects of temperature inactivation of penicillin-binding protein 2 on envelope growth in Escherichia coli

The transition from rod-shaped to spheroidal cells was studied in a temperature-sensitive strain (SP45) of Escherichia coli K12, carrying a mutation (pbpA) in the gene coding for penicillin-binding protein 2 (PBP-2). This transition imposed by the restrictive temperature was associated with reduction of peptidoglycan/surface area and of cellular osmotic stability. Addition of nalidixic acid (20 micrograms/ml) at the temperature shift from 30 to 42 degrees C resulted in lysis of some cells and appearance of spheroidal bulges along the cylinders in other cells, consistent with the hypothesis of envelope weakening due to inactivation of PBP-2.