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Induction of Copper Resistance in Plant-Pathogenic Bacteria Exposed to Glutamate, Plant Extracts, Phosphate Buffer, and Some Antibiotics. M. Goto, Faculty of Agriculture, Shizuoka University, 836 Ohya, Shizuoka 422, Japan; T. Hikota(2), T. Kyuda(3), and M. Nakajima(4). (2)Biological Research Laboratory, Tomono Nohyaku Co., Ltd., Ohyanagi, Shimada 427-01, Japan; (3)(4)Faculty of Agriculture, Shizuoka University, 836 Ohya, Shizuoka 422, Japan. Phytopathology 83:1449-1453. Accepted for publication 23 July 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-1449.

In plant-pathogenic bacteria, minimum inhibitory concentrations of copper sulfate (CuSO4) in aqueous solution ranged between 1 and 10 M, 0.01 or less than those determined with potato-dextrose agar plates. The viability of bacteria in CuSO4 solution greatly increased when glutamate was supplemented at concentrations of 10 g/ml or more. Bacteria survived well in CuSO4-glutamate mixtures in which concentrations of free cupric ions were much higher than the lethal doses, indicating that a novel copper resistance was induced in the presence of glutamate. Resistance was induced with other amino acids and amides but not with sugars, sugar alcohols, or organic acids. Copper resistance also was induced by phosphate buffer at 25 mM or more, tetracycline hydrochloride and oxytetracycline hydrochloride at 100 g/ml, and plant extracts. The induction of copper resistance generally was more pronounced in copper-resistant bacteria than in copper-sensitive ones. The induction of copper resistance took place in water droplets placed on injured plant leaves carrying copper deposits but not on intact leaves. Copper resistance thus induced was transient, and elevated copper resistance was restored in the absence of these factors.

Additional keywords: complexation of cupric ions, copper bactericides, transitory copper resistance.