Transient Loss of Plasmid Mediated Mercuric Ion Resistance After Freezing and Thawing of Pseudomonas Auerginosa

After freezing and thawing, Pseudomonas aeruginosa harboring a drug resistance plasmid (Hg , Strep ), became acutely sensitive to mercuric ions but not to streptomycin in the plating medium. Its sensitivity to both agents in the plating medium became more pronounced, suggesting a synergistic effect of the mercuric ions with streptomycin. This freeze-thaw-induced sensitivity was transient and capable of being repaired in a simple salts medium (0.5%K2HPO4 + 0.04%MJSO4 pH7.7). Transient wall and membrane damage were also observed in frozen-thawed preparations. From kinetics studies, repair of membrane damage preceded repair of wall damage and damage measured by mercuric ions and mercuric ions plus streptomycin. Osmotically shocked cells also were sensitive to mercuric ions, mercuric ions plus streptomycin and sodium lauryl sulfate, but not to sodium chloride or streptomycin alone. This sensitivity was transient and capable of repair in the same simple salts medium. Active transport of a non-metabolisable amino acid, a-amino isobutyric acid, was sensitive to mercuric ions and became more so after freezing and thawing. A freeze-thaw resistant mercuric ion dependent NADPH oxido-reductase was localized in the cytoplasm, and the enzyme and an intact outer membrane appear to be required for mercuric ion resistance in this strain. OHIOJ . SCI. 82(1): 59, 1982