Induction Kinetics of β-Lactamase Biosynthesis in Pseudomonas aeruginosa

Abstract

The induction of β-lactamase in Pseudomonas aeruginosa 1822s was studied using benzylpenicillin as inducer. The specific rate of β-lactamase formation was constant throughout an induction experiment. Above a threshold (20 μg/ml), the specific activity increased linearly with the concentration of the inducer. Removal of the inducer resulted in a rapid cessation of β-lactamase biosynthesis. Inhibition of protein synthesis by starvation for a required amino acid or by the addition of chloramphenicol also led to an instantaneous arrest in enzyme formation. In the absence of inducer, a basal β-lactamase activity was formed. The basal and the induced enzymes seem to be identical since they had the same substrate profile, electrophoretic mobility, and molecular weight. In all these respects, induction of β-lactamase in Pseudomonas aeruginosa is analogous to induction of the lac operon in Escherichia coli . However, there was a long, concentration-dependent lag before β-lactamase was induced. This can be explained by the outer penetration barrier decreasing the rate of inducer uptake. The lag was significantly shorter for lysozyme-ethylenediaminetetraacetic acid-produced spheroplasts than for intact cells. Induction was obtained with all β-lactam antibiotics tested, but not with other agents affecting the cell envelope.