Properties of β-Lactamase from Pseudomonas syringae

Pseudomonas syringae isolate BR2R produces tabtoxin, a β-lactam-containing antibiotic, and the causative agent of wildfire disease of green bean (Phaseolus vulgaris). β-Lactamase production has been suggested as the mechanism that protects P. syringae from tabtoxin. We sought to determine whether the organism produces β-lactamase and whether the enzyme plays a role in protection from this antibiotic. P. syringae and mutants defective in tabtoxin production and resistance produce β-lactamase. Three distinct β-lactamases with molecular weights of 41,000 were identified. The isoelectric points of the proteins were 6.1, 6.8, and 9.2. The enzymes preferentially hydrolyze cephalosporin. This investigation demonstrates that the organism produces multiple β-lactamases and describes characteristics of the proteins.