Motility and Chemotaxis of Erwinia Amylovora

Abstract

Environmental and cultural factors influence the motility of Erwinia amylovora by affecting either flagella synthesis of motility itself. Flagella synthesis is temperature dependent with an optimum at 18-23(DEGREES)C. However, bacterial cells grown at these temperatures are actively motile even at 35(DEGREES)C. The optimum pH for flagella synthesis is 6-8 although cells grown at the pH optimum are still motile at pH 9. For motility to occur, a chelating agent is required in the medium. An external energy source is not needed for motility although mannitol and glucose stimulate movement. Energy for motility is derived from oxygen dependent metabolism of endogenous energy sources but motility occurs under anaerobic conditions if an energy source is provided which can be metabolized in the absence of oxygen. Erwinia amylovora cells are not motile inside host tissues but become motile when placed in contact with free water at temperatures optimal for flagella synthesis.

Chemotaxis is also dependent on temperature and pH with an optimum temperature of 20-28(DEGREES)C and optimum pH of 6-8. Chemotaxis is best measured by a capillary assay using an incubation period of 30 minutes and a cell population not greater than 4 x 10('7) cells per ml. A medium consisting of 10('-3) M ethylenediamine tetraacetic acid, 10('-3) M mannitol, 10('-2) M MgCl(,2) and 10('-2) M potassium phosphate buffer at pH 7 was established for such assays.

Erwinia amylovora exhibits chemotaxis to apple nectar, to the organic acid fraction of apple nectar, to one amino acid, aspartate, and to several organic acids including malate, oxaloacetate, succinate, malonate, fumarate, and maleate. Erwinia amylovora is not attracted to any of the mono-, di-, or trisaccharides tested. All attractants are four or three carbon, dicarboxylic acids and response of E. amylovora to these attractants was uniformly inhibited by malate suggesting a single chemoreceptor site for all attractants. The chemoattractant response pattern of the isolate used in this study and that of an American Type Culture Collection isolate were identical.