J. Adler

Bio: J. Adler is an academic researcher. The author has contributed to research in topics: Positive chemotaxis & Chemotaxis. The author has an hindex of 1, co-authored 1 publications receiving 765 citations.

A method for measuring chemotaxis and use of the method to determine optimum conditions for chemotaxis by Escherichia coli.

Abstract: SUMMARY: Chemotaxis of a bacterium such as Escherichia coli is assayed by measuring the number of organisms attracted into a capillary tube containing an attractant. Rate of bacterial accumulation in capillaries and a concentration-response curve for l-aspartate taxis are presented and interpreted, and the effect of bacterial concentration is reported. Other parameters of the assay were studied, such as the volume of fluid in the capillary and the size of the capillary opening. The concentration gradient of chemical was also described. Escherichia coli chemotaxis requires EDTA to allow motility, a buffer to maintain the pH at its optimum near neutrality, and l-methionine if it cannot be synthesized. Under certain conditions there is stimulation by inorganic ions, either by K+ or, less effectively, by Na+. Chemotaxis is dependent on temperature, there being a 20-fold increase in the number of bacteria accumulating in a capillary when the temperature is raised from 20 to 30 °C.

Physics of chemoreception

Abstract: Statistical fluctuations limit the precision with which a microorganism can, in a given time T, determine the concentration of a chemoattractant in the surrounding medium. The best a cell can do is to monitor continually the state of occupation of receptors distributed over its surface. For nearly optimum performance only a small fraction of the surface need be specifically adsorbing. The probability that a molecule that has collided with the cell will find a receptor is Ns/(Ns + pi a), if N receptors, each with a binding site of radius s, are evenly distributed over a cell of radius a. There is ample room for many indenpendent systems of specific receptors. The adsorption rate for molecules of moderate size cannot be significantly enhanced by motion of the cell or by stirring of the medium by the cell. The least fractional error attainable in the determination of a concentration c is approximately (TcaD) - 1/2, where D is diffusion constant of the attractant. The number of specific receptors needed to attain such precision is about a/s. Data on bacteriophage absorption, bacterial chemotaxis, and chemotaxis in a cellular slime mold are evaluated. The chemotactic sensitivity of Escherichia coli approaches that of the cell of optimum design.

Cell-to-substratum adhesion and guidance of axonal elongation

Abstract: The behavior of axonal growth cones on surfaces with patterned variations in substratum was observed. Cells from sensory ganglia of 8-day-old chicken embryos were cultured on plastic petri dishes, plastic tissue culture dishes, and polyornithine-coated tissue culture dishes, all of which contained gridlike patterns of palladium (Pd) deposition. The results indicated that growth cones elongated on the Pd-shadowed areas vs areas lacking Pd deposits depending on the relative adhesivity of the growth cones to the substrata. In petri dishes, growth cones stay on the Pd; in tissue culture dishes, they cross from one surface to the other; and in polyornithine-coated dishes, they elongate for great distances on the Pd-free areas. Analyses of time-lapse movies showed that, on Pd-shadowed polyornithine dishes, growth cones often approach the Pd-coated areas and microspikes touch the Pd surface. Yet, the axon tip continues to elongate on the Pd-free polyornithine surface. The conclusion is offered that interactions between microspikes and the substratum adjacent to the growth cone are important determinants of the directions and pathways of axonal elongation.

Change in direction of flagellar rotation is the basis of the chemotactic response in Escherichia coli

Abstract: BERG and Anderson1 recently argued from existing evidence that bacteria swim by rotation of their helical flagella. Silver-man and Simon2 have now provided a clear demonstration of this. By means of antibodies specific for flagellar components, they tethered cells to microscope slides or to each other and observed rotation of the cell bodies. The cells were able to stop and to rotate in either direction. It seemed possible, as they proposed2, that cessation, or reversal of flagellar rotation might be involved in bacterial chemotaxis. Accordingly, we used wild-type and chemotaxis-defective mutant cells of Escherichia coli tethered to microscope slides in a manner similar to that of Silverman and Simon2, and stimulated them by sudden increases of chemotactic agents. We found that changes in the direction of flagellar rotation indeed constitute the basis of chemotaxis: addition of attractants causes counter clockwise (CCW) rotation, whereas repellents cause clockwise (CW) rotation.

Genomic and biochemical insights into the specificity of ETS transcription factors.

Abstract: ETS proteins are a group of evolutionarily related, DNA-binding transcriptional factors. These proteins direct gene expression in diverse normal and disease states by binding to specific promoters and enhancers and facilitating assembly of other components of the transcriptional machinery. The highly conserved DNA-binding ETS domain defines the family and is responsible for specific recognition of a common sequence motif, 5 � -GGA(A/T)-3 � . Attaining specificity for biological regulation in such a family is thus a conundrum. We present the current knowledge of routes to functional diversity and DNA binding specificity, including divergent properties of the conserved ETS and PNT domains, the involvement of flanking structured and unstructured regions appended to these dynamic domains, posttranslational modifications, and protein partnerships with other DNA-binding proteins and coregulators. The review emphasizes recent advances from biochemical and biophysical approaches, as well as insights from genomic studies that detect ETSfactor occupancy in living cells.

Chemotaxis in bacteria.

Abstract: Bacterial chemotaxis, the movement of motile bacteria toward or away from chemicals, was discovered nearly a century ago by Engelmann (43) and Pfeffer (70, 71) The subject was actively studied for about fifty years, but then there were very few reports until quite recently For reviews of the literature up to about 1960, see Berg (23) , Weibull (90) and Ziegler (92) The present review will restrict itself to the recent work on chemotaxis in Escherichia coli and Salmonella typhimurium, some of which is also covered in Berg’s review (23)