title: Complex patterns formed by motile cells of Escherichia coli.
abstract: When chemotactic strains of the bacterium Escherichia coli are inoculated on semi-solid agar containing mixtures of amino acids or sugars, the cells swarm outwards in a series of concentric rings: they respond to spatial gradients of attractants generated by uptake and catabolism. Cells also drift up gradients generated artificially, for example by diffusion from the tip of a capillary tube or by mixing. Here we describe conditions under which cells aggregate in response to gradients of attractant which they excrete themselves. When cells are grown in semi-solid agar on intermediates of the tricarboxylic acid cycle, they form symmetrical arrays of spots or stripes that arise sequentially. When cells in a thin layer of liquid culture are exposed to these compounds, spots appear synchronously, more randomly arrayed. In either case, the patterns are stationary. The attractant is a chemical sensed by the aspartate receptor. Its excretion can be triggered by oxidative stress. As oxygen is limiting at high cell densities, aggregation might serve as a mechanism for collective defence.
authors.affiliation: Department of Cellular and Developmental Biology, Harvard University, Cambridge, Massachusetts 02138.
authors.forename: E O
authors.initials: EO
authors.lastname: Budrene
authors.forename: H C
authors.initials: HC
authors.lastname: Berg
mesh_terms: D001224:Aspartic Acid / Q000502:physiology; D002465:Cell Movement; D002633:Chemotaxis; D002952:Citric Acid Cycle; D004926:Escherichia coli / Q000502:physiology*; D010100:Oxygen / Q000502:physiology
chemical_list: D001224:Aspartic Acid; D010100:Oxygen