Douglas A. Brown

Bio: Douglas A. Brown is an academic researcher from University of Colorado Boulder. The author has contributed to research in topics: Chemotaxis. The author has an hindex of 2, co-authored 3 publications receiving 2238 citations.

Chemotaxis in Escherichia coli analysed by Three-dimensional Tracking

Abstract: Chemotaxis toward amino-acids results from the suppression of directional changes which occur spontaneously in isotropic solutions.

Temporal stimulation of chemotaxis in Escherichia coli.

Abstract: We used the tracking microscope to study the chemotactic responses of E. coli to temporal gradients of L-glutamate generated in isotropic solutions by the action of the enzyme alanine aminotransferase. Positive gradients suppress directional changes which occur spontaneously in the absence of a stimulus. Negative gradients have little effect. The data can be fit with a model in which the suppression is proportional to the time rate of change of the fractional amount of chemoreceptor bound. The model accounts for the behavior of individual cells and populations of cells in spatial gradients. A computer simulation of the motion in spatial gradients indicates that if the bacteria have a “memory,” its decay time cannot be much longer than a few seconds. The relationship between the responses observed in these experiments and in experiments in which solutions of an attractant at different concentrations are mixed is discussed.

(bacterial taxis/temporal gradients/alanine aminotransfi

Abstract: We used the tracking microscope to study the chemotactic responses of E. coli to temporal gradients of L-glutamate generated in isotropic solutions by the action of the enzyme alanine aminotransferase. Positive gradients suppress directional changes which occur spon- taneously in the absence of a stimulus. Negative gradients have little effect. The data can be fit with a model in which the suppression is proportional to the time rate of change of the fractional amount of chemoreceptor bound. The model accounts for the behavior of individual cells and populations of cells in spatial gradients. A computer simulation of the motion in spatial gradients indicates that if the bacteria have a "memory," its decay time can- not be much longer than a few seconds. The relationship between the responses observed in these experiments and in experiments in which solutions of an attractant at dif- ferent concentrations are mixed is discussed. Tactic responses in bacteria occur when the intensity of a

Biomimicry of bacterial foraging for distributed optimization and control

Abstract: We explain the biology and physics underlying the chemotactic (foraging) behavior of E. coli bacteria. We explain a variety of bacterial swarming and social foraging behaviors and discuss the control system on the E. coli that dictates how foraging should proceed. Next, a computer program that emulates the distributed optimization process represented by the activity of social bacterial foraging is presented. To illustrate its operation, we apply it to a simple multiple-extremum function minimization problem and briefly discuss its relationship to some existing optimization algorithms. The article closes with a brief discussion on the potential uses of biomimicry of social foraging to develop adaptive controllers and cooperative control strategies for autonomous vehicles. For this, we provide some basic ideas and invite the reader to explore the concepts further.

Active Particles in Complex and Crowded Environments

Abstract: Differently from passive Brownian particles, active particles, also known as self-propelled Brownian particles or microswimmers and nanoswimmers, are capable of taking up energy from their environment and converting it into directed motion. Because of this constant flow of energy, their behavior can be explained and understood only within the framework of nonequilibrium physics. In the biological realm, many cells perform directed motion, for example, as a way to browse for nutrients or to avoid toxins. Inspired by these motile microorganisms, researchers have been developing artificial particles that feature similar swimming behaviors based on different mechanisms. These man-made micromachines and nanomachines hold a great potential as autonomous agents for health care, sustainability, and security applications. With a focus on the basic physical features of the interactions of self-propelled Brownian particles with a crowded and complex environment, this comprehensive review will provide a guided tour through its basic principles, the development of artificial self-propelling microparticles and nanoparticles, and their application to the study of nonequilibrium phenomena, as well as the open challenges that the field is currently facing.

Persister cells, dormancy and infectious disease

Abstract: Several well-recognized puzzles in microbiology have remained unsolved for decades. These include latent bacterial infections, unculturable microorganisms, persister cells and biofilm multidrug tolerance. Accumulating evidence suggests that these seemingly disparate phenomena result from the ability of bacteria to enter into a dormant (non-dividing) state. The molecular mechanisms that underlie the formation of dormant persister cells are now being unravelled and are the focus of this Review.

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.

Protein phosphorylation and regulation of adaptive responses in bacteria.

Abstract: Bacteria continuously adapt to changes in their environment. Responses are largely controlled by signal transduction systems that contain two central enzymatic components, a protein kinase that uses adenosine triphosphate to phosphorylate itself at a histidine residue and a response regulator that accepts phosphoryl groups from the kinase. This conserved phosphotransfer chemistry is found in a wide range of bacterial species and operates in diverse systems to provide different regulatory outputs. The histidine kinases are frequently membrane receptor proteins that respond to environmental signals and phosphorylate response regulators that control transcription. Four specific regulatory systems are discussed in detail: chemotaxis in response to attractant and repellent stimuli (Che), regulation of gene expression in response to nitrogen deprivation (Ntr), control of the expression of enzymes and transport systems that assimilate phosphorus (Pho), and regulation of outer membrane porin expression in response to osmolarity and other culture conditions (Omp). Several additional systems are also examined, including systems that control complex developmental processes such as sporulation and fruiting-body formation, systems required for virulent infections of plant or animal host tissues, and systems that regulate transport and metabolism. Finally, an attempt is made to understand how cross-talk between parallel phosphotransfer pathways can provide a global regulatory curcuitry.