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Physiology and Biochemistry

Chemotaxis of Erwinia amylovora. Asuncion K. Raymundo, Former graduate student, Department of Plant Pathology, University of Illinois, Urbana 61801, Present address of senior author: Department of Life Sciences, University of The Philippines at Los Baños, College, Laguna; Stephen M. Ries, associate professor, Department of Plant Pathology, University of Illinois, Urbana 61801. Phytopathology 70:1066-1069. Accepted for publication 17 May 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-1066.

Chemotaxis of Erwinia amylovora is temperature- and pH-dependent with an optimum temperature range of 20–28 C and pH 6–8. An incubation period of 30 min and a cell population not greater than 4 × 10⁷ cells per milliliter are optimal for chemotaxis studies. A medium consisting of 10^–3 M ethylene diaminetetraacetic acid, 10^–3 M mannitol, 10^–2 M MgCl₂ and 10^–2 M potassium phosphate buffer at pH 7 was established for assays. Using these assay conditions, E. amylovora exhibits positive chemotaxis to apple nectar, to the organic acid fraction of apple nectar, to one amino acid (aspartate), to the organic acids fumarate, malate, maleate, malonate, oxaloacetate, and succinate, but not to any of the sugars tested. All attractants are dicarboxylic acids and responses of E. amylovora are uniformly inhibited by malate, suggesting a single chemoreceptor site for all the attractants. The chemoattractant response pattern of our strain and that of American Type Culture Collection strain 19382 of E. amylovora was identical.