Attractant was added to a suspension of bacteria (the background concentration of attractant) and then these bacteria were exposed to a yet higher concentration of attractant in a capillary. Chemotaxis was measured by determining how many bacteria accumulated in the capillary. The response range for chemotaxis lies between the threshold concentration and the saturating concentration. The breadth of this range is different for attractants detected by different chemoreceptors. Attractants detected by the same chemoreceptor can have their response ranges in widely different places. Over the center of the response range (on a logarithmic scale), bacteria give similar sized responses to similar fractional increases of concentration, i.e. they respond to ratios of attractant concentration, but the response peaks at the center of the range. The size of the response is different for attractants detected by different chemoreceptors. For a detectable response, a smaller increase in attractant concentration is needed for attractants detected by some chemoreceptors than for attractants detected by others. Although the data are inadequate, it appears that the Weber law may be observed over a wide range of concentrations for some attractants but not for others. In the Appendix we aim to explain some of these results in terms of the interaction of an attractant with its chemoreceptor according to the law of mass action.

, or valine. Bacteria grown in a proline-containing medium were, in addition, attracted to proline. Chemotaxis toward amino acids is shown to be mediated by at least two detection systems, the aspartate and serine chemoreceptors. The aspartate chemoreceptor was nonfunctional in the aspartate taxis mutant, which showed virtually no chemotaxis toward aspartate, glutamate, or methionine, and reduced taxis toward alanine, asparagine, cysteine, glycine, and serine. The serine chemoreceptor was nonfunctional in the serine taxis mutant, which was defective in taxis toward alanine, asparagine, cysteine, glycine, and serine, and which showed no chemotaxis toward threonine. Additional data concerning the specificities of the amino acid chemoreceptors with regard to amino acid analogues are also presented. Finally, two essentially nonoxidizable amino acid analogues, a-aminoisobutyrate and a-methylaspartate, are shown to be attractants for E. coli, demonstrating that extensive metabolism of attractants is not required for amino acid taxis. Motile Escherichia coli cells are attracted to a variety of chemicals, including sugars (2, 4, 10), amino acids (3, 4, 10), and oxygen (2, 3). In this report, we summarize present knowledge concerning chemotaxis toward amino acids in this organism. The questions we have attempted to answer are the following: (i) which of the L-amino acids commonly found in proteins are attractive; (ii) how many detection systems, or chemoreceptors, are involved in taxis toward amino acids; (iii) what are the specificities of these chemoreceptors for the common amino acids and various analogues; and (iv) what is the relationship between amino acid metabolism and amino acid taxis? We now present evidence that 10 of the amino acids commonly occurring in proteins can attract E. coli, and that two systems, the "aspartate chemoreceptor" and the "serine chemoreceptor," are responsible for detecting at least eight of these attractants. Although the two chemoreceptors are most sensitive to aspartate and serine, respectively, each can also detect a large number of structurally related amino acids and analogues. Extensive metabolism of amino acids is neither required nor sufficient for attraction. MATERIALS AND METHODS Bacteria. B14 is E. coli K-12, male, strA, and wild-type for chemotaxis (5). AW405 is E. coli K-12, F-, ara, gal-1, gal-2, lac, xyl, his-4, leu, thr, tonA, tsx, strA, and wildtype for chemotaxis (7). The isolation of the serine taxis mutant, AW518, from AW405 has been described elsewhere (10). The aspartate taxis mutant, AW539, was obtained from AW405 by use of the same selection procedure, except that tryptone semisolid agar was replaced by aspartate semisolid agar, described below. Bacteria swarming on aspartate semisolid agar form a single distinct ring which results from aspartate taxis. The cells used in selecting for an aspartate taxis mutant were first mutagenized with N-methyl-N'-nitro-Nnitrosoguanidine by the method of Adelberg, Mandel, and Chen (1). Media. Tryptone broth contained 1% Difco tr...

Abstract.-Mutants of Escherichia coli K12 have been found which fail to carry out chemotaxis toward certain chemicals only. One mutant exhibits greatly reduced chemotaxis toward L-serine but has no detectable defect either in uptake or in oxidative metabolism of that compound. Another mutant is not attracted to D-galactose and certain related sugars. There is a correlation between the galactose chemotaxis defect and a defect in galactose uptake, perhaps indicating a common component for chemotaxis and uptake systems. The results are discussed in terms of a model for chemotaxis in which attractants are detected by specific "chemoreceptors."Escherichia coli are chemotactic, that is, they are attracted to certain chemicals.1, 2 A model for bacterial chemotaxis has been proposed2 in which classes of sterically related compounds are recognized by specific "chemoreceptors." Information from all chemoreceptors is channeled through a common pathway to the flagella where a response is initiated. The model predicts two classes of nonchemotactic mutants. One class is defective in the common pathway, reducing chemotaxis to all chemicals ("generally nonchemotactic mutants"). The other has defects in specific chemoreceptors, reducing chemotaxis to certain chemicals ("specifically nonchemotactic mutants"). Generally nonchemotactic mutants of Escherichia coli K12 have been isolated, characterized,3 and studied genetically4' 5 in our laboratory. In this report we describe two specifically nonchemotactic mutants, one defective in taxis to a group of amino acids and the other to a group of sugars. Materials and Methods.-Bacteria: The serine taxis mutant, AW518, was isolated from AW405 (E. coli K12, wild type for chemotaxis, gal-i, gal-2, thr, leu, his-4, thi, lac, xyl, ara, str-r, ton A-r, tsx-r) by means of a selection procedure described previously.3 In this procedure, cells are placed at the center of a tryptone semisolid plate. Rings of chemotactic bacteria swarm out from the center in response to amino acid gradients created by bacterial growth.1 Cells remaining at the center after swarming has occurred are used to inoculate a fresh plate. After several such transfers, the center is enriched in nonflagellated, abnormally flagellated, paralyzed, and nonchemotactic mutants.W3109 (gal-9), a galactose operon extreme polar mutant of E. coli K12 obtained from Dr. E. Lederberg, was found to be a galactose taxis mutant. AW520, a gal+ revertant of W3109 (also lami-r and ton A-r), was used in the experiments described in this paper. To select for revertants to normal galactose taxis, about 109 cells of AW520 (grown, harvested, and washed as in chemotaxis experiments) in 0.1 ml of chemotaxis medium were spread in a streak on a semisolid galactose plate. On such a plate, bacteria chemotactic toward galactose form a dense ring' easily visible after 12 hr. After 3 days at 350C in a wet incubator, chemotaxis rings were faintly visible along the border of the AW520 streak. A single colony isolate, AW521, from one of the rings showed normal c...

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Occurrence records for named, native Australian millipedes from the Global Biodiversity Information Facility (GBIF) and the Atlas of Living Australia (ALA) were compared with the same records from the Millipedes of Australia (MoA) website, compiled independently by the author. The comparison revealed some previously unnoticed errors in MoA, and a much larger number of errors and other problems in the aggregated datasets. Errors have been corrected in MoA and in some data providers’ databases, but will remain in GBIF and ALA until data providers have supplied updates to these aggregators. An audit by a specialist volunteer, as reported here, is not a common occurrence. It is suggested that aggregators should do more, or more effective, data checking and should query data providers when possible errors are detected, rather than simply disclaim responsibility for aggregated content.