Effect of Cadmium on the Morphology, Membrane Integrity and Permeability of Pseudomonas putida

Cadmium-adapted Pseudomonas putida exhibited a long lag phase (6 h) on incubation in a defined medium containing 3 mM-Cd2+. During this time extensive blebbing of the outer membrane was observed by electron microscopy and polyphosphate granules containing Cd2+ were present in the cells. Cells from exponential-phase cultures of cadmium-adapted P. putida were found in clusters. They were much smaller than control cells grown without cadmium, and contained electron-dense aggregates. Cadmium-adapted cells released more lipopolysaccharide and protein into the external medium than did control cells; the addition of Ca2+, but not Mg2+, to the medium prevented this increased release. Cadmium-adapted cells also showed greatly increased sensitivity towards certain antibiotics, including the aminoglycosides, cyclic polypeptides and doxycycline. It is suggested that this is related to changes in membrane structure.