Chemotaxis In Bacteria Research Articles

Periplasmic Binding Protein-Based Detection of Maltose Using Liposomes: A New Class of Biorecognition Elements in Competitive Assays

A periplasmic binding protein (PBP) was investigated as a novel binding species in a similar manner to an antibody in a competitive enzyme linked immunosorbent assay (ELISA), resulting in a highly sensitive and specific assay utilizing liposome-based signal amplification. PBPs are located at high concentrations (10(-4) M) between the inner and outer membranes of gram negative bacteria and are involved in the uptake of solutes and chemotaxis of bacteria toward nutrient sources. Previous sensors relying on PBPs took advantage of the change in local environment or proximity of site-specific fluorophore labels resulting from the significant conformational shift of these proteins' two globular domains upon target binding. Here, rather than monitoring conformational shifts, we have instead utilized the maltose binding protein (MBP) in lieu of an antibody in an ELISA. To our knowledge, this is the first PBP-based sensor without the requirement for engineering site-specific modifications within the protein. MBP conjugated fluorescent dye-encapsulating liposomes served to provide recognition and signal amplification in a competitive assay for maltose using amylose magnetic beads in a microtiter plate-based format. The development of appropriate binding buffers and competitive surfaces are described, with general observations expected to extend to PBPs for other analytes. The resulting assay was specific for d-(+)-maltose versus other sugar analogs including d-(+)-raffinose, sucrose, d-trehalose, d-(+)-xylose, d-fructose, 1-thio-β-d-glucose sodium salt, d-(+)-galactose, sorbitol, glycerol, and dextrose. Cross-reactivity with d-lactose and d-(+)-glucose occurred only at concentrations >10(4)-fold greater than d-(+)-maltose. The limit of detection was 78 nM with a dynamic range covering over 3 orders of magnitude. Accurate detection of maltose as an active ingredient in a pharmaceutical preparation was demonstrated. This method offers a significant improvement over existing enzymatic detection approaches that cannot discriminate between maltose and glucose and over existing fluorescence resonance energy transfer (FRET)-based detection methods that are sensitivity limited. In addition, it opens up a new strategy for the development of biosensors to difficult analytes refractory to immunological detection.

Gas/liquid sensing via chemotaxis of Euglena cells confined in an isolated micro-aquarium

We demonstrate on-chip gas/liquid sensing by using the chemotaxis of live bacteria (Euglena gracilis) confined in an isolated micro-aquarium, and gas/liquid permeation through porous polydimethylsiloxane (PDMS). The sensing chip consisted of one closed micro-aquarium and two separated bypass microchannels along the perimeter of the micro-aquarium. Test gas/liquid and reference samples were introduced into the two individual microchannels separately, and the gas/liquid permeated through the PDMS walls and dissolved in the micro-aquarium water, resulting in a chemical concentration gradient in the micro-aquarium. By employing the closed micro-aquarium isolated from sample flows, we succeeded in measuring the chemotaxis of Euglena for a gas substance quantitatively, which cannot be achieved with the conventional flow-type or hydro-gel-type microfluidic devices. We found positive (negative) chemotaxis for CO2 concentrations below (above) 15%, with 64 ppm as the minimum concentration affecting the cells. We also observed chemotaxis for ethanol and H2O2. By supplying culture medium via the microchannels, the Euglena culture remained alive for more than 2 months. The sensing chip is thus useful for culturing cells and using them for environmental toxicity/nutrition studies by monitoring their motion.

Ecology and Physics of Bacterial Chemotaxis in the Ocean

Intuitively, it may seem that from the perspective of an individual bacterium the ocean is a vast, dilute, and largely homogeneous environment. Microbial oceanographers have typically considered the ocean from this point of view. In reality, marine bacteria inhabit a chemical seascape that is highly heterogeneous down to the microscale, owing to ubiquitous nutrient patches, plumes, and gradients. Exudation and excretion of dissolved matter by larger organisms, lysis events, particles, animal surfaces, and fluxes from the sediment-water interface all contribute to create strong and pervasive heterogeneity, where chemotaxis may provide a significant fitness advantage to bacteria. The dynamic nature of the ocean imposes strong selective pressures on bacterial foraging strategies, and many marine bacteria indeed display adaptations that characterize their chemotactic motility as "high performance" compared to that of enteric model organisms. Fast swimming speeds, strongly directional responses, and effective turning and steering strategies ensure that marine bacteria can successfully use chemotaxis to very rapidly respond to chemical gradients in the ocean. These fast responses are advantageous in a broad range of ecological processes, including attaching to particles, exploiting particle plumes, retaining position close to phytoplankton cells, colonizing host animals, and hovering at a preferred height above the sediment-water interface. At larger scales, these responses can impact ocean biogeochemistry by increasing the rates of chemical transformation, influencing the flux of sinking material, and potentially altering the balance of biomass incorporation versus respiration. This review highlights the physical and ecological processes underpinning bacterial motility and chemotaxis in the ocean, describes the current state of knowledge of chemotaxis in marine bacteria, and summarizes our understanding of how these microscale dynamics scale up to affect ecosystem-scale processes in the sea.

A multidomain hub anchors the chromosome segregation and chemotactic machinery to the bacterial pole

The cell poles constitute key subcellular domains that are often critical for motility, chemotaxis, and chromosome segregation in rod-shaped bacteria. However, in nearly all rods, the processes that underlie the formation, recognition, and perpetuation of the polar domains are largely unknown. Here, in Vibrio cholerae, we identified HubP (hub of the pole), a polar transmembrane protein conserved in all vibrios, that anchors three ParA-like ATPases to the cell poles and, through them, controls polar localization of the chromosome origin, the chemotactic machinery, and the flagellum. In the absence of HubP, oriCI is not targeted to the cell poles, chemotaxis is impaired, and a small but increased fraction of cells produces multiple, rather than single, flagella. Distinct cytoplasmic domains within HubP are required for polar targeting of the three ATPases, while a periplasmic portion of HubP is required for its localization. HubP partially relocalizes from the poles to the mid-cell prior to cell division, thereby enabling perpetuation of the polar domain in future daughter cells. Thus, a single polar hub is instrumental for establishing polar identity and organization.

Diversity and chemotaxis of soil bacteria with antifungal activity against Fusarium wilt of banana

The chemotactic response of bacteria to root exudates plays an important role in the colonization of bacteria in the rhizosphere. In this study, 420 strains of antifungal bacteria against Fusarium oxysporum f. sp. cubense (Foc) were screened for chemotaxis based on a cheA molecular diagnostic method. A total of 124 strains with antifungal efficiencies of 27.26-67.14% generated a characteristic band of cheA. The chemotaxis of 97 bacterial strains producing a cheA band was confirmed using the drop assay and swarm plate assay using catechol, p-hydroxybenzoic acid, salicylic acid, and asparagine as the attractants. A phylogenetic analysis based on restriction fragment length polymorphisms (RFLPs) and 16S rDNA sequences indicated that the 124 chemotactic antagonists of Foc were affiliated with 18 species of Paenibacillaceae, Bacillaceae, Streptomycineae, Enterobacteriaceae, and Pseudomonadaceae. The chemical composition of banana root exudates were analyzed by GC-MS, and 62 compounds, including alkanes, alkenes, naphthalenes, benzenes, and alcohols, were evaluated. Five representative antagonists of Foc showed 1.76- to 7.75-fold higher chemotactic responses than the control to seven compounds in banana root exudates, as determination by capillary assays.

A Gastric Pathogen Moves Chemotaxis in a New Direction

For almost 50 years, Escherichia coli has been the model for understanding how bacteria orient their movement in response to chemical cues, but recent studies of chemotaxis in other bacteria have revealed interesting variations from prevailing paradigms. Investigating the human pathogen Helicobacter pylori, Amieva and colleagues [mBio 2(4):e00098-11, 2011] discovered a new chemotaxis regulator, ChePep, which modulates swimming behavior through the canonical histidine-aspartate phosphorelay system. Functionally conserved among the epsilonproteobacteria, ChePep is essential for H. pylori to navigate deep into the stomach’s gastric glands and may be an attractive target for novel antibiotics.

Heterodisaccharide 4-O-(N-acetyl-β-d-glucosaminyl)-d-glucosamine is an effective chemotactic attractant for Vibrio bacteria that produce chitin oligosaccharide deacetylase

To investigate the attractant effect of 4-O-(N-acetyl-β-D-glucosaminyl)-D-glucosamine (GlcNAc-GlcN) in the chemotaxis of Vibrio bacteria that produce carbohydrate esterase (CE) family 4 chitin oligosaccharide deacetylase (COD), an enzyme that catalyzes the production of GlcNAc-GlcN from N,N'-diacetylchitobiose (GlcNAc)(2). The chemotactic effect of disaccharides from chitin on several strains of Vibrio bacteria was investigated using an agar gel lane-migration method. The results demonstrated that GlcNAc-GlcN functions as an effective chemoattractant in the CE family 4 COD-producing vibrios, Vibrio parahaemolyticus and Vibrio alginolyticus. In contrast, this phenomenon was not observed in Vibrio nereis or Vibrio furnissii, which lack genes encoding this enzyme. From transmission electron microscope observation of V. parahaemolyticus cells following the chemotaxis assay, GlcNAc-GlcN appears to stimulate polar flagellum rotation. GlcNAc-GlcN is a specific chemoattractant for the CE family 4 COD-producing vibrios, V. parahaemolyticus and V. alginolyticus. It was clarified for the first time that GlcNAc-GlcN functions as a signalling molecule in the chemotaxis of Vibrio bacteria that have an ability to produce CE family 4 COD, which generate GlcNAc-GlcN from (GlcNAc)(2).

Accessing a hidden conformation of the maltose binding protein using accelerated molecular dynamics.

Periplasmic binding proteins (PBPs) are a large family of molecular transporters that play a key role in nutrient uptake and chemotaxis in Gram-negative bacteria. All PBPs have characteristic two-domain architecture with a central interdomain ligand-binding cleft. Upon binding to their respective ligands, PBPs undergo a large conformational change that effectively closes the binding cleft. This conformational change is traditionally viewed as a ligand induced-fit process; however, the intrinsic dynamics of the protein may also be crucial for ligand recognition. Recent NMR paramagnetic relaxation enhancement (PRE) experiments have shown that the maltose binding protein (MBP) - a prototypical member of the PBP superfamily - exists in a rapidly exchanging (ns to µs regime) mixture comprising an open state (approx 95%), and a minor partially closed state (approx 5%). Here we describe accelerated MD simulations that provide a detailed picture of the transition between the open and partially closed states, and confirm the existence of a dynamical equilibrium between these two states in apo MBP. We find that a flexible part of the protein called the balancing interface motif (residues 175–184) is displaced during the transformation. Continuum electrostatic calculations indicate that the repacking of non-polar residues near the hinge region plays an important role in driving the conformational change. Oscillations between open and partially closed states create variations in the shape and size of the binding site. The study provides a detailed description of the conformational space available to ligand-free MBP, and has implications for understanding ligand recognition and allostery in related proteins.

Alteration of immune functions and Th1/Th2 cytokine balance in nicotine-induced murine macrophages: Immunomodulatory role of eugenol and N-acetylcysteine

The aim of this study was to evaluate the immune functions by nicotine-induced murine peritoneal macrophages, and Th1/Th2 cytokine balance in it, and concurrently to establish the immunomodulatory role of eugenol, and N-acetylcysteine in nicotine-induced macrophages. Eugenol was isolated from Ocimum gratissimum, and characterized by HPLC, FTIR, and 1H NMR. The cytotoxic effect of isolated eugenol was studied in murine peritoneal macrophages at various concentrations (0.1–50 μg/ml) using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. To evaluate the immunomodulatory role of eugenol and N-acetylcysteine, ROS and nitrite generations, phenotype functions by macrophages were studied. The effect of eugenol and N-acetylcysteine on the release of Th1 cytokines (TNF-α, IL-12) and Th2 cytokines (IL-10, TGF-β) was measured by ELISA, and the expression of these cytokines at mRNA level were analyzed by real-time PCR. Eugenol, at a dose of 15 μg/ml, showed less cytotoxicity to the macrophages and it significantly reduced the nicotine-induced ROS, NO generation, and iNOSII expression. Similar kinds of response were observed in the presence of N-acetylcysteine (1 μg/ml). We have found the decreased adherence, chemotaxis, phagocytosis and intracellular killing of bacteria in nicotine treated macrophages, whereas eugenol and N-acetylcysteine with nicotine treatment enhanced these cellular functions by macrophages significantly (p < 0.05). Eugenol and N-acetylcysteine were found to down regulate the Th1 cytokines in nicotine treated macrophages with concurrent activation of Th2 responses. These findings strongly enhanced our understanding of the molecular mechanism leading to nicotine-induced suppression of immune functions, and provide additional rationale for the application of anti-inflammatory therapeutic approaches by eugenol, and N-acetylcysteine for different inflammatory diseases prevention and treatment during nicotine toxicity.

Immunomodulatory Role ofOcimum gratissimumand Ascorbic Acid against Nicotine-Induced Murine Peritoneal MacrophagesIn Vitro

The aim of this present study was to evaluate the immune functions and immune responses in nicotine-induced (10 mM) macrophages and concurrently establish the immunomodulatory role of aqueous extract of Ocimum gratissimum (Ae-Og) and ascorbic acid. In this study, nitrite generations and some phenotype functions by macrophages were studied. Beside that, release of Th1 cytokines (TNF-α, IL-12) and Th2 cytokines (IL-10, TGF-β) was measured by ELISA, and the expression of these cytokines at mRNA level was analyzed by real-time PCR. Ae-Og, at a dose of 10 μg/mL, significantly reduced the nicotine-induced NO generation and iNOSII expression. Similar kinds of response were observed with supplementation of ascorbic acid (0.01 mM). The administration of Ae-Og and ascorbic acid increased the decreased adherence, chemotaxis, phagocytosis, and intracellular killing of bacteria in nicotine-treated macrophages. Ae-Og and ascorbic acid were found to protect the murine peritoneal macrophages through downregulation of Th1 cytokines in nicotine-treated macrophages with concurrent activation of Th2 responses. These findings strongly enhanced our understanding of the molecular mechanism leading to nicotine-induced suppression of immune functions and provide additional rationale for application of anti-inflammatory therapeutic approaches by O. gratissimum and ascorbic acid for different inflammatory disease prevention and treatment during nicotine toxicity.

Sheared bioconvection in a horizontal tube

The recent interest in using microorganisms for biofuels is motivation enough to study bioconvection and cell dispersion in tubes subject to imposed flow. To optimize light and nutrient uptake, many microorganisms swim in directions biased by environmental cues (e.g. phototaxis in algae and chemotaxis in bacteria). Such taxes inevitably lead to accumulations of cells, which, as many microorganisms have a density different to the fluid, can induce hydrodynamic instabilites. The large-scale fluid flow and spectacular patterns that arise are termed bioconvection. However, the extent to which bioconvection is affected or suppressed by an imposed fluid flow and how bioconvection influences the mean flow profile and cell transport are open questions. This experimental study is the first to address these issues by quantifying the patterns due to suspensions of the gravitactic and gyrotactic green biflagellate alga Chlamydomonas in horizontal tubes subject to an imposed flow. With no flow, the dependence of the dominant pattern wavelength at pattern onset on cell concentration is established for three different tube diameters. For small imposed flows, the vertical plumes of cells are observed merely to bow in the direction of flow. For sufficiently high flow rates, the plumes progressively fragment into piecewise linear diagonal plumes, unexpectedly inclined at constant angles and translating at fixed speeds. The pattern wavelength generally grows with flow rate, with transitions at critical rates that depend on concentration. Even at high imposed flow rates, bioconvection is not wholly suppressed and perturbs the flow field.

Exploding solutions for a nonlocal quadratic evolution problem

We consider a nonlinear parabolic equation with fractional diffusion which arises from modelling chemotaxis in bacteria. We prove the wellposedness, continuation criteria and smoothness of local solutions. In the repulsive case we prove global wellposedness in Sobolev spaces. Finally in the attractive case, we prove that for a class of smooth initial data the L_x^\infty -norm of the corresponding solution blows up in finite time. This solves a problem left open by Biler and Woyczy\'nski [Biler, P. and Woyczy\'Nski, W.A.: Global and exploding solutions for nonlocal quadratic evolution problems. SIAM J. Appl. Math. {\bf 59} (1999), no. 3, 845-869].

Microfluidics for bacterial chemotaxis

Microfluidics is revolutionizing the way we study the motile behavior of cells, by enabling observations at high spatial and temporal resolution in carefully controlled microenvironments. An important class of such behavior is bacterial chemotaxis, which plays a fundamental role in a broad range of processes, including disease pathogenesis, biofilm formation, bioremediation, and even carbon cycling in the ocean. In biophysical research, bacterial chemotaxis represents a powerful model system to understand how cells and organisms sense and respond to gradients. Using microfluidics to study chemotaxis of free-swimming bacteria presents experimental challenges that are distinct from those arising in chemotaxis studies of surface-adherent cells. Recently, these challenges have been met by the development of advanced microdevices, able to generate flow-free, steady gradients of arbitrary shape. Much attention to date has been focused on tool development. Yet, we are now at an exciting turning point where science begins to balance technology. Indeed, recent microfluidic studies provided new insights on both the mechanisms governing bacterial gradient sensing (e.g. tuning of response sensitivity, discrimination between conflicting gradients) and the large-scale consequences of chemotaxis (e.g. in the oceans). Here we outline the principles underlying recently proposed gradient generators for bacterial chemotaxis, illustrate the advantage of the microfluidic approach through selected examples, and identify a broader set of scientific questions that may now be addressed with this rapidly developing technology. The latest generation of microfluidic gradient generators, in particular, holds appeal for both biophysicists seeking to unravel the fundamental mechanisms of bacterial chemotaxis, and ecologists wishing to model chemotaxis in realistic environments. Time is ripe for a deeper integration between technology and biology in fully bringing to bear microfluidics on studies of this fascinating microbial behavior.

Defining Network Topologies that Can Achieve Biochemical Adaptation

Many signaling systems show adaptation-the ability to reset themselves after responding to a stimulus. We computationally searched all possible three-node enzyme network topologies to identify those that could perform adaptation. Only two major core topologies emerge as robust solutions: a negative feedback loop with a buffering node and an incoherent feedforward loop with a proportioner node. Minimal circuits containing these topologies are, within proper regions of parameter space, sufficient to achieve adaptation. More complex circuits that robustly perform adaptation all contain at least one of these topologies at their core. This analysis yields a design table highlighting a finite set of adaptive circuits. Despite the diversity of possible biochemical networks, it may be common to find that only a finite set of core topologies can execute a particular function. These design rules provide a framework for functionally classifying complex natural networks and a manual for engineering networks. For a video summary of this article, see the PaperFlick file with the Supplemental Data available online.

Requisite variety: more on Gaia

PurposeThe purpose of this paper is to mention a set of suggestions for analysing the current financial crisis, but with reservations about the usefulness of one based on Ashby's principle of requisite variety. The reservations are supported by reference to a mechanism of chemotaxis in bacteria. A recent publication concerning the Gaia hypothesis and global warming is reviewed.Design/methodology/approachThe aim is to review developments on the internet, especially those of general cybernetic interest.FindingsThe significance of complexity, in government and management, is not disputed, but doubts are expressed about validity of laws that are purported to treat it quantitatively. A pessimistic view of world future is due to James Lovelock, the originator of the Gaia hypothesis, though there is some reason to believe he is more hopeful than is suggested in an interview.Practical implicationsThe reservations about Ashby's treatment of complexity are essentially theoretical and do not negate findings based on its robust and imprecise application. Lovelock indicates a means of saving the Earth from disastrous climate change but has little hope that it will be implemented.Originality/valueIt is hoped this is a valuable periodic review.

Some nonlinear challenges in biology

Driven by a deluge of data, biology is undergoing a transition to a more quantitative science. Making sense of the data, building new models, asking the right questions and designing smart experiments to answer them are becoming ever more relevant. In this endeavour, nonlinear approaches can play a fundamental role. The biochemical reactions that underlie life are very often nonlinear. The functional features exhibited by biological systems at all levels (from the activity of an enzyme to the organization of a colony of ants, via the development of an organism or a functional module like the one responsible for chemotaxis in bacteria) are dynamically robust. They are often unaffected by order of magnitude variations in the dynamical parameters, in the number or concentrations of actors (molecules, cells, organisms) or external inputs (food, temperature, pH, etc). This type of structural robustness is also a common feature of nonlinear systems, exemplified by the fundamental role played by dynamical fixed points and attractors and by the use of generic equations (logistic map, Fisher–Kolmogorov equation, the Stefan problem, etc.) in the study of a plethora of nonlinear phenomena. However, biological systems differ from these examples in two important ways: the intrinsic stochasticity arising from the often very small number of actors and the role played by evolution. On an evolutionary time scale, nothing in biology is frozen. The systems observed today have evolved from solutions adopted in the past and they will have to adapt in response to future conditions. The evolvability of biological system uniquely characterizes them and is central to biology. As the great biologist T Dobzhansky once wrote: ‘nothing in biology makes sense except in the light of evolution’.

Functional asymmetry in Caenorhabditis elegans taste neurons and its computational role in chemotaxis

Chemotaxis in Caenorhabditis elegans, like chemotaxis in bacteria, involves a random walk biased by the time derivative of attractant concentration, but how the derivative is computed is unknown. Laser ablations have shown that the strongest deficits in chemotaxis to salts are obtained when the ASE chemosensory neurons (ASEL and ASER) are ablated, indicating that this pair has a dominant role. Although these neurons are left-right homologues anatomically, they exhibit marked asymmetries in gene expression and ion preference. Here, using optical recordings of calcium concentration in ASE neurons in intact animals, we demonstrate an additional asymmetry: ASEL is an ON-cell, stimulated by increases in NaCl concentration, whereas ASER is an OFF-cell, stimulated by decreases in NaCl concentration. Both responses are reliable yet transient, indicating that ASE neurons report changes in concentration rather than absolute levels. Recordings from synaptic and sensory transduction mutants show that the ON-OFF asymmetry is the result of intrinsic differences between ASE neurons. Unilateral activation experiments indicate that the asymmetry extends to the level of behavioural output: ASEL lengthens bouts of forward locomotion (runs) whereas ASER promotes direction changes (turns). Notably, the input and output asymmetries of ASE neurons are precisely those of a simple yet novel neuronal motif for computing the time derivative of chemosensory information, which is the fundamental computation of C. elegans chemotaxis. Evidence for ON and OFF cells in other chemosensory networks suggests that this motif may be common in animals that navigate by taste and smell.

Pseudomonas aeruginosa as a model microorganism for investigation of chemotactic behaviors in ecosystem

Motile bacteria sense changes in the concentration of chemicals in environments and respond in a behavioral manner. This behavioral response is called chemotaxis. Bacterial chemotaxis can be viewed as an important prelude to metabolism, prey-predator relationships, symbiosis, infections, and other ecological interactions in biological communities. Genome analysis reveals that a large number of environmental motile bacteria possess a number of genes involved in chemosensing and chemotatic signal transduction. Pseudomonas aeruginosa has a very complex chemosensory system with more than 20 chemotaxis (che) genes in five distinct clusters and 26 chemoreceptor (methyl-accepting chemotaxis protein [mcp]) genes. Among the 26 MCPs of P. aeruginosa, nine have been identified as MCPs for amino acids, inorganic phosphate, oxygen, ethylene, and volatile chlorinated aliphatic hydrocarbons, whereas 3 MCPs were demonstrated to be involved in biofilm formation and biosynthesis of type IV pilus. Six che genes are essential for chemotactic responses, while genes in Pil-Chp cluster and Wsp cluster are involved in type IV pilus synthesis and twitching motility and biofilm formation, respectively. P. aeruginosa, with its complex chemotaxis system, is a better model microorganism for investigating ecological aspects of chemotaxis in environmental bacteria than Escherichia coli and Salmonella enterica serovar Typhimurium, which possess a relatively simpler chemotaxis system.

A Novel Optimization Algorithm Inspired by Bacteria Behavior Patterns

This paper proposes a novel optimization algorithm inspired by bacteria behavior patterns for foraging. Most bacteria can trace attractant chemical molecules for foraging. This tracing capability of bacteria called chemotaxis might be optimized for foraging because it has been evolved for few millenniums. From this observation, we developed a new optimization algorithm based on the chemotaxis of bacteria in this paper. We first define behavior and decision rules based on the behavior patterns of bacteria and then devise an optimization algorithm with these behavior and decision rules. Generally bacteria have a quorum sensing mechanism that makes it possible to effectively forage, but we leave its implementation as a further work for simplicity. Thereby, we call our algorithm a simple bacteria cooperative optimization (BCO) algorithm. Our simple BCO is tested with four function optimization problems on various' parameters of the algorithm. It was found from experiments that the simple BCO can be a good framework for optimization.

Noise generation, amplification and propagation in chemotactic signaling systems of living cells

Theoretical considerations of stochastic signal transduction in living cells have revealed the gain-fluctuation relation, which provides a theoretical framework to describe quantitatively how noise is generated, amplified and propagated along a signaling cascade in living cells. We chose the chemotactic signaling of bacteria and eukaryotic cells as a typical example of noisy signal transduction and applied the gain-fluctuation relation to these signaling systems in order to analyze the effects of noise on signal transduction. Comparing our theoretical analysis with the experimental results of chemotaxis in bacteria Escherichia coli and eukaryote Dictyostelium discoideum revealed that noise in signal transduction systems limits the cells’ chemotactic ability and contributes to their behavioral variability. Based on the kinetic properties of signaling molecules in living cells, the gain-fluctuation relation can quantitatively explain stochastic cellular behaviors.