Negative Chemotaxis Research Articles

Olfactory Selection Preferences of Pagiophloeus tsushimanus (Coleoptera: Curculionidae) Adults Toward Lauraceae Plants.

Cinnamomum camphora is a broad-spectrum insect-repelling tree species because of its high content of terpenoids. However, it is curious that Pagiophloeus tsushimanus, a recently recorded wood-boring pest, has widely infested C. camphora plantations across various administrative districts in Shanghai. The larvae, being concealed within the trunk of C. camphora trees, exhibit characteristics such as hidden activity, strong destructiveness, and being difficult to control. While the primary host plant for P. tsushimanus is C. camphora, preliminary observations have shown that the pest can also complete its life cycle on Cinnamomum chekiangensis and Phoebe chekiangensis. To explore the host selection preference of this beetle, the present study aimed to investigate the olfactory selection behavior of P. tsushimanus adults towards C. camphora, C. chekiangensis, and P. chekiangensis. Results from choice and no-choice tests indicated that both male and female adults exhibited a feeding preference for C. camphora twigs, with females showing a preference for laying eggs on camphor tree twigs as well. Volatile compounds unique in camphor trees were significantly higher in relative content than those on the other two plants that were detected. The Y-shaped olfactometer experiments and electroantennography measurements results showed that male and female adults of P. tsushimanus had a positive chemotaxis towards volatiles released by C. camphora and a negative chemotaxis towards volatiles released by C. chekiangensis or P. chekiangensis. Overall, the findings suggest that both male and female adults have a selective preference for volatiles released by the camphor tree, and this provides a theoretical basis for monitoring and controlling the occurrence of this weevil pest.

TAXES OF DICYEMIDS (PHYLUM DICYEMIDA).

Dicyemids (Phylum Dicyemida) are endosymbionts present in the kidneys of benthic cephalopods. They usually consist of 10 to 40 cells and are characterized by 2 distinct body types: vermiform individuals and infusoriform larvae. Vermiform individuals remain attached to the internal surface of the host's renal appendages, while infusoriform larvae leave the renal sac to search for a new host. To investigate how dicyemids respond to various host and environmental cues, we evaluated phototaxis, chemotaxis, thigmotaxis, and rheotaxis responses of vermiform individuals and infusoriform larvae of 2 dicyemid species in a laboratory setting. Vermiform individuals did not exhibit phototaxis and chemotaxis to the major components of the host: urine, tissue fluids, or extracts of the host gills. However, they showed positive thigmotaxis and positive rheotaxis to slow water flow, probably contributing to enabling attachment to the renal appendages and remaining in the renal sac, respectively. The infusoriform larvae exhibited negative chemotaxis to host blood and negative thigmotaxis, but there was no evidence of phototaxis and rheotaxis. Negative thigmotaxis may facilitate the release of infusoriform embryos from the renal appendages. Negative chemotaxis to the host blood suggests that the infusoriform larvae do not enter through the vascular system to gain access to the renal sac, so the process by which infusoriform larvae enter the cephalopod host is yet to be determined.

Rotary FoF1-ATP Synthase-Driven Flasklike Pentosan Colloidal Motors with ATP Synthesis and Storage.

We report the hierarchical assembly of a chloroplast-derived rotary FoF1-ATPase motor-propelled flasklike pentosan colloidal motor (FPCM) with the ability of the synthesis, storage, and triggered release of biological energy currency ATP. These streamlined and submicrometer-sized hollow flasklike pentosan colloidal motors are prepared by combining a soft-template-based hydrothermal polymerization with a vacuum infusion of chloroplast-derived proteoliposomes containing rotary FoF1-ATPase motors. The generation of proton motive force across the proteoliposomes by injecting an acidic buffer solution promotes the rotation of FoF1-ATPase motors to drive the self-propelled motion of FPCMs, accompanying the inner ATP synthesis and storage. These rotary FoF1-ATPase motor-powered FPCMs exhibit a chemotactic behavior by migrating from their neck opening to their round bottom along a proton gradient of the external environment (negative chemotaxis). Such rotary biomolecular motor-driven flasklike pentosan colloidal motors with ATP synthesis and on-demand release make them promising candidates for engineering novel intelligent nanocarriers to actively regulate cellular metabolism.

Negative chemotaxis of Ligilactobacillus agilis BKN88 against gut-derived substances

Ligilactobacillus agilis is a motile lactic acid bacterium found in the gastrointestinal tracts of animals. The findings of our previous study suggest that the motility of L. agilis BKN88 enables gut colonization in murine models. However, the chemotactic abilities of motile lactobacilli remain unknown. This study aimed to identify the gut-derived chemoeffectors and their corresponding chemoreceptors in L. agilis BKN88. Chemotaxis assays with chemotactic and non-chemotactic (ΔcheA) L. agilis strains revealed that low pH, organic acids, and bile salts served as repellents. L. agilis BKN88 was more sensitive to bile and acid than the gut-derived non-motile lactobacilli, implying that L. agilis might utilize motility and chemotaxis instead of exhibiting stress tolerance/resistance. L. agilis BKN88 contains five putative chemoreceptor genes (mcp1–mcp5). Chemotaxis assays using a series of chemoreceptor mutants revealed that each of the five chemoreceptors could sense multiple chemoeffectors and that these chemoreceptors were functionally redundant. Mcp2 and Mcp3 sensed all tested chemoeffectors. This study provides further insights into the interactions between chemoreceptors and ligands of motile lactobacilli and the unique ecological and evolutionary features of motile lactobacilli, which may be distinct from those of non-motile lactobacilli.

Speed-up of traveling waves by negative chemotaxis

We consider the traveling wave speed for Fisher-KPP (FKPP) fronts under the influence of repulsive chemotaxis and provide an almost complete picture of its asymptotic dependence on parameters representing the strength and length-scale of chemotaxis. Our study is based on establishing the convergence to the porous medium FKPP traveling wave and a hyperbolic FKPP-Keller-Segel traveling wave in certain asymptotic regimes. In this way, it clarifies the relationship between three equations that have each garnered intense interest on their own. Our proofs involve a variety of techniques ranging from entropy methods and decay of oscillations estimates to a general description of the qualitative behavior to the hyperbolic FKPP-Keller-Segel equation. For this latter equation, we, as a part of our limiting arguments, establish a new explicit lower bound on the minimal traveling wave speed and provide a novel construction of traveling waves that extends the known existence range to all parameter values.

Reproduction of bacterial chemotaxis by a non-living self-propelled object

Taxic behavior as a response to an external stimulus is a fundamental function of living organisms. Some bacteria successfully implement chemotaxis without directly controlling the direction of movement. They periodically alternate between run and tumble, i.e., straight movement and change in direction, respectively. They tune their running period depending on the concentration gradient of attractants around them. Consequently, they respond to a gentle concentration gradient stochastically, which is called “bacterial chemotaxis.” In this study, such a stochastic response was reproduced by a non-living self-propelled object. We used a phenanthroline disk floating on an aqueous solution of Fe^{2+}. The disk spontaneously alternated between rapid motion and rest, similar to the run-and-tumble motion of bacteria. The movement direction of the disk was isotropic independent of the concentration gradient. However, the existing probability of the self-propelled object was higher at the low-concentration region, where the run length was longer. To explain the mechanism underlying this phenomenon, we proposed a simple mathematical model that considers random walkers whose run length depends on the local concentration and direction of movement against the gradient. Our model adopts deterministic functions to reproduce the both effects, which is instead of stochastic tuning the period of operation used in the previous reports. This allows us to analyze the proposed model mathematically, which indicated that our model reproduces both positive and negative chemotaxis depending on the competition between the local concentration effect and it’s gradient effect. Owing to the newly introduced directional bias, the experimental observations were reproduced numerically and analytically. The results indicate that the directional bias response to the concentration gradient is an essential parameter for determining bacterial chemotaxis. This rule might be universal for the stochastic response of self-propelled particles in living and non-living systems.

Chemorepulsion: Moving away from improper attractions

Eukaryotic cells can undergo chemorepulsion, but the molecular mechanisms behind this phenomenon have remained unclear. Using Dictyostelium cells, a new study shows that competition of two ligands for the same receptors results in chemorepulsion, thus revealing a simple rule for eukaryotic cells to achieve negative chemotaxis.

Competition between chemoattractants causes unexpected complexity and can explain negative chemotaxis

Negative chemotaxis, where eukaryotic cells migrate away from repellents, is important throughout biology, for example, in nervous system patterning and resolution of inflammation. However, the mechanisms by which molecules repel migrating cells are unknown. Here, we use predictive modeling and experiments with Dictyostelium cells to show that competition between different ligands that bind to the same receptor leads to effective chemorepulsion. 8-CPT-cAMP, widely described as a simple chemorepellent, is inactive on its own and only repels cells when it acts in combination with the attractant cAMP. If cells degrade either competing ligand, the pattern of migration becomes more complex; cells may be repelled in one part of a gradient but attracted elsewhere, leading to populations moving in different directions in the same assay or converging in an arbitrary place. More counterintuitively still, two chemicals that normally attract cells can become repellent when combined. Computational models of chemotaxis are now accurate enough to predict phenomena that have not been anticipated by experiments. We have used them to identify new mechanisms that drive reverse chemotaxis, which we have confirmed through experiments with real cells. These findings are important whenever multiple ligands compete for the same receptors.

Kinetic Asymmetry versus Dissipation in the Evolution of Chemical Systems as Exemplified by Single Enzyme Chemotaxis.

Single enzyme chemotaxis is a phenomenon by which a nonequilibrium spatial distribution of an enzyme is created and maintained by concentration gradients of the substrate and product of the catalyzed reaction. These gradients can arise either naturally through metabolism or experimentally, e.g., by flow of materials through microfluidic channels or by use of diffusion chambers with semipermeable membranes. Numerous hypotheses regarding the mechanism of this phenomenon have been proposed. Here, we discuss a mechanism based solely on diffusion and chemical reaction and show that kinetic asymmetry, a difference in the transition state energies for dissociation/association of substrate and product, and diffusion asymmetry, a difference in the diffusivities of the bound and free forms of the enzyme, are the determinates of the direction of chemotaxis and can result in either positive or negative chemotaxis, both of which have been demonstrated experimentally. Exploration of these fundamental symmetries that govern nonequilibrium behavior helps to distinguish between possible mechanisms for the evolution of a chemical system from initial to the steady state and whether the principle that determines the direction a system shifts when exposed to an external energy source is based on thermodynamics or on kinetics with the latter being supported by the results of the present paper. Our results show that, while dissipation ineluctably accompanies nonequilibrium phenomena, including chemotaxis, systems do not evolve to maximize or minimize dissipation but rather to attain greater kinetic stability and accumulate in regions where their effective diffusion coefficient is as small as possible. The chemotactic response to the chemical gradients formed by other enzymes participating in a catalytic cascade provides a mechanism for forming loose associations known as metabolons. Significantly, the direction of the effective force due to these gradients depends on the kinetic asymmetry of the enzyme and so can be nonreciprocal, where one enzyme is attracted to another enzyme, but the other enzyme is repelled by the one, in seeming contradiction to Newtons third law. This nonreciprocity is an important ingredient in the behavior of active matter.

Recursively positive and negative chemotaxis coupling with reaction kinetics in self-organized inanimate motion

Reconstructing recursive chemotaxis in inanimate self-propelled objects is inevitable in the development of recursively and autonomously artificial mass transport systems. However, the fabrication of inanimately recursive chemotaxis has been extremely challenging because of the difficulty in introducing competitive positive and negative feedback into an inanimate self-propelled object. Herein, a coumarin derivative (coumarin, 4-methylcoumarin (4-MC), or 6-methylcoumarin (6-MC))-based disk floated on water as a self-propelled object exhibited characteristic features of motion; these features include continuous motion, repetition between positive and negative chemotaxis to the Na3PO4 powder as a base stimulus, and oscillatory motion above the Na3PO4 powder depending on the Na3PO4 density of the powder and the functional group of coumarin derivatives. The mechanism of the characteristic features of motion to the base stimulus is discussed in relation to the surface tension of the coumarin derivatives as the driving force of motion and the reaction rate of the hydrolysis between coumarin derivatives and OH– obtained from Na3PO4. This study suggests a novel avenue for developing a recursive chemotactic system coupled with reaction kinetics in self-organized motion.

Pathway selection by an active droplet.

We report the movement of an active 1-pentanol drop within a closed Y-shaped channel subjected to geometrical and chemical asymmetry. A Y-shaped channel was configured with an angle of 120° between any two arms, which serves as the closed area of movement for the active drop. The arm where the 1-pentanol drop is introduced in the beginning is considered the source arm, and the center of the Y-shaped structure is the decision region. The drop always selects a specific route to move away from the decision region. The total probability of pathway selection excludes the possibility of the drop choosing the source channel. Remarkably, the active drop exhibits a strong sense of navigation for both geometrically and chemically asymmetric environments with accuracy rates of 80% and 100%, respectively. The pathway selection in a chemically asymmetric channel is a demonstration of the artificial negative chemotaxis, where the extra confined drop acts as a chemo-repellent. To develop a better understanding of our observations, a numerical model is constructed, wherein the particle is subjected to a net force which is a combined form of - (i) Yukawa-like repulsive interaction force (acting between the drop and the walls), (ii) a self-propulsion force, (iii) a drag, and (iv) a stochastic force. The numerics can capture all the experimental findings both qualitatively and quantitatively. Finally, a statistical analysis validates conclusions derived from both experiments and numerics.

Microplastic leachates disrupt the chemotactic and chemokinetic behaviours of an ecosystem engineer (Mytilus edulis)

The massive contamination of the environment by plastics is an increasing global scientific and societal concern. Knowing whether and how these pollutants affect the behaviour of keystone species is essential to identify environmental risks effectively. Here, we focus on the effect of plastic leachates on the behavioural response of the common blue mussel Mytilus edulis, an ecosystem engineer responsible for the creation of biogenic structures that modify the environment and provide numerous ecosystem functions and services. Specifically, we assess the effect of virgin polypropylene beads on mussels’ chemotactic (i.e. a directional movement in response to a chemical stimulus) and chemokinetic (i.e. a non-directional change in movement properties such as speed, distance travelled or turning frequency in response to a chemical stimulus) responses to different chemical cues (i.e. conspecifics, injured conspecifics and a predator, the crab Hemigrapsus sanguineus). In the presence of predator cues, individual mussels reduced both their gross distance and speed, changes interpreted here as an avoidance behaviour. When exposed to polypropylene leachates, mussels moved less compared to control conditions, regardless of the cues tested. Additionally, in presence of crab cues with plastic leachates, mussels significantly changed the direction of movement suggesting a leachate-induced loss of their negative chemotaxis response. Taken together, our results indicate that the behavioural response of M. edulis is cue-specific and that its anti-predator behaviour as well as its mobility are impaired when exposed to microplastic leachates, potentially affecting the functioning of the ecosystem that the species supports.

It’s the Little Things: The Role of Microscopic Life Stages in Maintaining Kelp Populations

Kelp forests are experiencing broad scale declines in abundance and shifts in latitudinal ranges in many areas of the world due to numerous environmental stressors, especially those associated with climate change. While the majority of studies on kelp ecology have focused exclusively on the macroscopic sporophyte life stage, a growing number of studies is showing quite convincingly that the microscopic zoospore and gametophyte life stages can be important to establishing spatial patterns in these marine forests, and in facilitating their recovery following deforestation. Unfortunately, their microscopic sizes have made them difficult to study in the field, leading to a ‘black box’ surrounding what we know about their ecologies. However, advances in experimental methodologies and a growing number of laboratories studying kelp microscopic life stages are revealing how they are affected by variability in environmental conditions, and are providing a clearer picture of how kelp forests might respond to a changing ocean climate. These studies have largely revealed that kelps can disperse over a wide range of distances, enhanced by the synchronous release and vertical transport of zoospores into shallower water, and by floating rafts of reproductive thalli. Settlement on the benthos is facilitated by both positive and negative chemotaxis, and by active selection of microhabitats that favor their growth and survival. Following settlement and subsequent germination, the haploid gametophytes can delay their development and form a bank of microscopic forms that persist during periods that are unfavorable for the large sporophyte populations, or they can develop and undergo sexual reproduction during which they respond to variability in environmental conditions. In particular, they are strongly affected by increases in irradiance (PAR, UVA + UVB) and temperature, decreases in nutrients and salinity, and by sedimentation and grazing. However, the manner in which they respond to these stressors varies among species and with their geographic distributions, which is integral to establishing biogeographic patterns in the large sporophyte populations. Given these factors are expected to change as the ocean climate changes, these species-specific responses have significant implications for future patterns of distribution and abundance of these iconic marine forests.

PROTECTIVE FEATURES OF LOBOPHORA VARIEGATA METHANOLIC EXTRACT (LVME) ON COGNITIVE BEHAVIOUR AND REDOX HOMEOSTASIS IN N-NITROSODIETHYLAMINE TREATED DROSOPHILA MELANOGASTER

Objective: The protecting influence of methanolic extract of seaweed (Lobophora variegata) on cognitive as well as biochemical indices in N-Nitrosodiethylamine (NDEA, a potent carcinogen) treated Drosophila melanogaster is evaluated.
 Methods: In this study, Flies are divided into four groups; group 1–(control), group 2-flies were treated with 0.01% NDEA in food medium, group 3–with 0.01% NDEA and 0.01% Lobophora variegata methanolic extract (LVME) and group 4-with 0.01% LVME alone.
 Results: Behavioural abnormalities (negative geotaxis, phototaxis, smell and taste chemotaxis, hygrotaxis and thermotaxis) were quantitatively deviated in NDEA treated flies compared to control but were tend to be normalized in LVME treated flies. The contents of protein carbonyl, thiobarbituric acid reactive substance (TBARS), protein thiol and lipid peroxides were noticeably augmented in NDEA treated flies than control flies and correspondingly tend to normalize in LVME treated groups. Further, superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), glutathione peroxidase (GPX) and reduced glutathione (GSH) were decreased in NDEA treated group and were significantly increased (p<0.05) in LVME treated groups.
 Conclusion: It is well known that seaweed extracts contain numerous beneficial phytochemicals in abundantly. From our investigation, we found that the 0.01% LVME is efficient in reverting the abnormal behaviours and restoring the redox homeostasis of NDEA induced carcinogenesis in Drosophila melanogaster. Our investigation indicates that these phytochemicals could prevent the abnormalities in behaviour and redox homeostasis during carcinogenesis in D. melanogaster.

Competition Between Chemoattractants Causes Unexpected Complexity and Can Explain Negative Chemotaxis

Competition Between Chemoattractants Causes Unexpected Complexity and Can Explain Negative Chemotaxis

Relative Diffusivities of Bound and Unbound Protein Can Control Chemotactic Directionality.

Enzyme-based systems have been shown to undergo chemotactic motion in response to their substrate gradient. This phenomenon has been exploited to direct the motion of enzymes and enzyme-attached particles to specific locations in space. Here, we propose a new kinetic model to analyze the directional movement of an ensemble of protein molecules in response to a gradient of the ligand. We also formulate a separate model to probe the motion of enzyme molecules in response to a gradient of the substrate under catalytic conditions. The only input for the new enzymatic model is the Michaelis-Menten constant which is the relevant measurable constant for enzymatic reactions. We show how our model differs from previously proposed models in a significant manner. For both binding and catalytic reactions, a net movement up the ligand/substrate gradient is predicted when the diffusivity of the ligand/substrate-bound protein is lower than that of the unbound protein (positive chemotaxis). Conversely, movement down the ligand/substrate gradient is expected when the diffusivity of the ligand/substrate-bound protein is higher than that of the unbound protein (negative chemotaxis). However, there is no net movement of protein/enzyme when the diffusivities of the bound and free species are equal. The work underscores the critical importance of measuring the diffusivity of the bound protein and comparing it with that of the free protein.

Engineering motile aqueous phase-separated droplets via liposome stabilisation

There are increasing efforts to engineer functional compartments that mimic cellular behaviours from the bottom-up. One behaviour that is receiving particular attention is motility, due to its biotechnological potential and ubiquity in living systems. Many existing platforms make use of the Marangoni effect to achieve motion in water/oil (w/o) droplet systems. However, most of these systems are unsuitable for biological applications due to biocompatibility issues caused by the presence of oil phases. Here we report a biocompatible all aqueous (w/w) PEG/dextran Pickering-like emulsion system consisting of liposome-stabilised cell-sized droplets, where the stability can be easily tuned by adjusting liposome composition and concentration. We demonstrate that the compartments are capable of negative chemotaxis: these droplets can respond to a PEG/dextran polymer gradient through directional motion down to the gradient. The biocompatibility, motility and partitioning abilities of this droplet system offers new directions to pursue research in motion-related biological processes.

Self-adaptive enzyme-powered micromotors with switchable propulsion mechanism and motion directionality

Switchable chemotaxis is vital for motile microorganisms seeking benefits or to avoid harm. Inspired by nature, and for the first time, we demonstrate an artificial enzyme-powered micromotor that can autonomously regulate the propulsion mechanism, as well as motion directionality, by solely sensing the change of fuel concentration (Cf) in its surroundings. The as-designed micromotors have a pot-like microstructure with ureases immobilized on the inner surface. With the confined effect of the pot-like microstructure and unique features of the urease catalytic reaction, the molecular products are further reacted into ions, and their propulsion mechanism can be reversibly adjusted between ionic diffusiophoresis and microbubble recoils when Cf changes. Consequently, the as-developed micromotors under magnetic field are able to self-turn back if the local Cf differs greatly in their surroundings, indicating the achievement of positive and negative chemotaxis by sensing local Cf. Meanwhile, the micromotors also show highly enhanced migration speed by microbubble ejection, up to 60 μm/s, around 30 body lengths per second at physiological urea concentrations. Furthermore, they have an outer surface of mesoporous silica which is easily functionalized for applications such as stimuli-responsive delivery-associated therapies. This work will promote “smart” artificial micro/nanomotors for in vivo biomedical applications.

Modulated Viscosity-Dependent Parameters for MHD Blood Flow in Microvessels Containing Oxytactic Microorganisms and Nanoparticles

This work’s primary purpose is to implement a numerical study that simulates blood flow through a microvessel involving oxytactic microorganisms and nanoparticles. The oxytactic microorganisms exhibit negative chemotaxis to gradients of oxygen (oxygen repellents). These microorganisms are to batter infected hypoxic tumor cells as drug-carriers. The viscosity of blood is to vary with temperature, shear-thinning, and nanoparticle concentration. We have formulated a mathematical model then simplified it under assumptions of long wavelength and low Reynold’s number. The resulting non-linear coupled differential equation system is solved numerically with the MATHEMATICA software aid using the built-in command (ParametricNDSolve). This study treated all non-dimensional parameters defined in terms of viscosity to be variables (VP-Model), unlike some previous literature attempts that have considered these parameters mentioned above as constants (CP-Model). The achieved results assured the reliability of the (VP-Model) over the (CP-Model). Our results reveal that temperature and microorganism density increase with the thermophoresis parameter. The impact of increasing the Brownian motion parameter is to increase temperature and lessen microorganism density. Outcomes also indicate an enhancement in the microorganism density towards the hypoxic tumor regions located aside the microvessel walls by boosting oxygen concentrations in the streamflow. The current study is believed to provide further opportunities to improve drug-carrier applications in hypoxic tumor regions by better recognizing the flow features, heat, and mass transfer in such zones.

Toxicological implications of amplifying the antibacterial activity of gallic acid by immobilisation on silica particles: A study on C. elegans

Immobilisation of natural compounds on solid supports to amplify antimicrobial properties has reported successful results, but modifications to physico-chemical properties can also imply modifications from a toxicological viewpoint. This work aimed to study the immobilising process of gallic acid in the antibacterial activity of L. innocua and its toxicological properties in vivo using Caenorhabditis elegans. The experiment was based on obtaining the minimum bactericidal concentration for free and immobilised gallic acid by comparing lethality, locomotion behaviour, chemotaxis and thermal stress resistance on C.elegans at those concentrations. The results showed a lowering minimum bactericidal concentration and modifications to nematode responses. Increased lethality and velocity of movements was observed. Immobilisation increased the repellent effect of gallic acid with a negative chemotaxis index. Thermal stress resistance was also affected, with higher mortality for immobilised gallic acid compared to bare particles and free gallic acid. Thus despite evidencing a generalised increase in the toxicity of gallic acid in vivo, lowering the minimum bactericidal concentration allowed a bacterial reduction of 99 % with less than one third of mortality for the nematodes exposed to free gallic acid.