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Bacteria track chemical gradients using a biased random walk, a process called chemotaxis. Experiments suggest that bacteria also communicate during this process. Using a mathematical model, we find that sufficiently strong communication succeeds in keeping a population of bacteria together but slows down chemotaxis. However, if the secretion of the communication molecule is coupled to the detection of the external chemoattractant, chemotaxis can be faster than without communication. This result assumes that cells can detect and subtract the average of the chemoattractant over the population, a mechanism we term adaptive communication. Intriguingly, in this regime we predict that, even though blocking the communication receptors should slow down chemotaxis, overexpressing them should also slow it down, and partially blocking or underexpressing them may actually speed it up. Our work provides physical insights on how communication and chemotaxis are connected and may help explain why chemotaxing bacteria communicate.

Understanding bacterial behavior in confined environments is helpful for elucidating microbial ecology and developing strategies to manage bacterial infections. While extensive research has focused on bacterial motility on surfaces and in porous media, chemotaxis in confined spaces remains poorly understood. Here, we investigate the chemotaxis of Escherichia coli within microfluidic lanes under a linear concentration gradient of L-aspartate. We demonstrate that E. coli exhibits significantly enhanced chemotaxis in lanes with sidewalls compared to open surfaces. We attribute this phenomenon primarily to the intrinsic chiral clockwise circular motion of surface-swimming bacteria and the subsequent alignment effect upon collision with the sidewalls. By varying lane widths, we identify that an 8 μm width-approximating the radius of bacterial circular swimming on surfaces-maximizes chemotactic drift velocity. These results are supported by both experimental observations and stochastic simulations, establishing a clear proportional relationship between optimal lane width and the radius of bacterial circular swimming. Further geometric analysis provides an intuitive understanding of this phenomenon. Our results may offer insights into bacterial navigation in complex biological environments such as host tissues and biofilms, providing a preliminary step toward exploring microbial ecology in confined habitats and potential strategies for controlling bacterial infections.

Bacterial chemotaxis has long been viewed as operating near the physical limits of sensing, as originally articulated by Berg and Purcell. Recent information-theoretic analyses challenge this view, suggesting thatEscherichia coliuses only a small fraction of the information available in ligand arrival statistics to bias its motion. How should such low information efficiency be interpreted at the level of behavior? Here, I argue that chemotactic performance is shaped not only by information transmission and noise, but by the strategy of movement itself. Using simple scaling arguments and minimal models, I show how run-and-tumble chemotaxis can remain robust to noise through symmetry and temporal averaging, even when internal information processing is inefficient. Comparing bacterial and eukaryotic chemotaxis highlights how different sensing strategies convert physical limits into observable behavior. These considerations suggest that low information efficiency need not imply poor performance, but may instead reflect an evolved balance between robustness, simplicity, and function.

Chemotaxis is the directional motion of objects in response to chemical gradients, a process that drives navigation in micro/nanomotors, enabling a bio-inspired transition toward autonomous direction control. However, current studies lack consistent mechanistic justification, definition, and standardized experimental validation. This review summarizes key physical principles governing active chemotaxis, surveys experimental strategies for generating chemical gradients and quantifying responses, and examines how individual chemotactic mechanisms and long-range, anisotropic chemical interactions give rise to emergent collective behaviors, while outlining prospective applications. Together, these efforts establish a principled engineering framework for advancing chemotaxis as a robust functional navigation modality in synthetic micro/nanomotors.

Chemotaxis, or the following of chemical concentration gradients, is essential for microbes to locate nutrients. However, microbes often display paradoxical behaviors, such as Escherichia coli being repelled by several amino acids. Here, we explore chemotaxis towards a moving source and demonstrate that when multiple nutrients are released from the source repulsion from certain nutrients actually improves chemotaxis towards the source. Because a moving source leaves most of the nutrient plume behind it, simply following the concentration gradient results in aiming behind the source and potentially failing to intercept it. However, when attraction to a fast-diffusing nutrient and repulsion from a slow-diffusing nutrient are combined, motion in a new direction emerges and the chance of intercepting the source is increased up to six-fold. We demonstrate that this "differential strategy" is robust against numerous variations, including order-of-magnitude increases in the repellent release rate. Finally, we leverage existing data to show that E. coli is attracted to fast-diffusing amino acids and repelled by slow-diffusing ones, suggesting it may utilize a differential strategy and providing an explanation for its repulsion from these amino acids. Our results thus illuminate new possibilities in how microbes can integrate signals from multiple gradients to accomplish challenging chemotactic tasks.

Understanding chemotaxis at the molecular level is challenging, as individual enzyme molecules cannot sense chemical gradients across their nanometer-sized bodies. Typical theoretical models encompass chemotaxis under constant, externally imposed gradients; however, this overlooks a critical feedback loop, where the active enzymes themselves reshape the imposed gradients through catalysis. In this work, we investigate the principles of active molecular chemotaxis using a Fokker-Planck model for an ATP-driven kinase-phosphatase system. Using experimentally relevant enzyme concentration ranges (∼nM), we demonstrate that the chemotactic velocity of enzymes does not simply respond linearly to chemical gradients, as commonly observed in microscale systems driven by diffusiophoresis. Instead, it emerges from a nonlinear coupling between the enzyme's spatial distribution, its conformational state (free/bound-state ratio), and chemical gradients modulated by catalytic reactions. As a result, the spatial profile of chemotactic velocity transitions between monotonic and nonmonotonic regimes, depending on substrate availability. Furthermore, we find that high catalyst concentrations can amplify the effective interaction between enzymes, forming a cascade that is critical for collective assemblies such as metabolon formation. To understand these complex interactions, we construct chemotactic velocity maps as a function of enzyme concentration, energy, and substrate availability, offering a set of design principles. This work clarifies the distinct roles of energy, gradients, and enzyme free/bound states in molecular motion, highlighting a fundamental difference between nano and microscale systems, and provides a theoretical framework for designing advanced autonomous active molecular systems.

Bacillus subtilis is a model for cell differentiation, capable of transitioning between distinct states: a sessile, chained state (often associated with biofilm formation), and a motile, planktonic state. This transition is governed by a complex regulatory network that includes alternative sigma factor-D (σD), which drives the expression of genes for autolysins, flagellar biosynthesis, and chemotaxis, resulting in separated, flagellated, motile cells. Although the conserved transcription-coupled repair factor mutation frequency decline (Mfd) is best known for resolving stalled RNA polymerase (RNAP) during DNA repair, its involvement in cell differentiation during the stationary phase remains poorly understood. This research shows that in the absence of Mfd translocation or RNAP recruitment, RNAP completes transcription of motility genes more frequently, despite unchanged σD transcript levels. Increased transcription of the σD-dependent motility regulon led to greater flagellation; however, swimming motility and pH taxis were paradoxically reduced, indicating that Mfd is required to translate flagellar gene expression into functional motility. Notably, Mfd-deficient cells failed to maintain chained subpopulations, indicating an additional role in sustaining population heterogeneity. These findings reveal a previously unrecognized function of Mfd as an RNAP-modulating factor that coordinates motility gene expression, thereby expanding our understanding of how transcription-coupled repair proteins influence bacterial physiology and behavior under non-proliferative conditions.IMPORTANCEThe mutation frequency decline (Mfd) enzyme mediates transcription-coupled repair in transcribed genes by directly interacting with RNA polymerase (RNAP) during transcription of coding sequences. However, whether the Mfd factor regulates gene expression associated with adaptations unrelated to DNA repair and mutagenesis remains vague. Here, we show that Mfd regulates the completion of full transcripts of genes that confer swimming motility, chemotaxis, and cell heterogeneity in Bacillus subtilis. Furthermore, we identified the Mfd's translocase activity and its interaction with RNAP as key elements of this regulation. Therefore, Mfd's importance in bacterial physiology and adaptation goes beyond DNA repair.

Plant pathogens possess about twice as many chemoreceptors as the bacterial average, suggesting broad chemotactic capacities. The signals recognized by most phytopathogen chemoreceptors are unknown, and the reasons for this elevated chemoreceptor number is unclear. We identified the signals recognized by three chemoreceptors, PacH, PacI and PacG, in the global phytopathogen Pectobacterium atrosepticum. The ligand-binding domains (LBDs) of these chemoreceptors share modest sequence similarity, but the signals they recognize are structurally similar, and their biosynthetic pathways are interwoven. Whereas PacH and PacI recognized benzoate derivatives, including salicylate, vanillin and p-hydroxybenzoate, PacG bound agmatine, feruloylagmatine and p-coumaroylagmatine. These compounds are known plant defense compounds, their production is induced by pathogen attack, and they typically accumulate at infection sites. All compounds, except agmatine, induced chemoattraction, which was abolished by mutations in the corresponding genes. Agmatine competed with feruloylagmatine and p-coumaroylagmatine for PacG-LBD binding in vitro and antagonized chemotaxis in vivo. A mutant in pacG, but not in other chemoreceptor genes, showed reduced virulence in planta. We report high-resolution structures of PacG-LBD that were used for ligand-docking experiments to identify its binding pocket. PacH, PacI and PacG homologs were identified in other important phytopathogens belonging to the Burkholderia, Erwinia, Ralstonia, Pectobacterium and Dickeya genera. This is the first report of chemotaxis to feruloylagmatine, p-coumaroylagmatine and p-methoxybenzoate, expanding the range of chemoeffectors. Bacteria thus exploit plant defense responses by moving to compounds that are secreted at infection sites in response to pathogen attack. Chemotaxis to plant defense compounds may be a means to access infected plants and infection sites.

Trichomonas vaginalis is an extracellular parasite that inhabits the human genital tract, yet little is known about how it senses and responds to the complex vaginal microbial ecosystem. Here, we show that T. vaginalis exhibits chemotactic behavior on semisolid surfaces, forming multicellular assemblies that coordinate collective migration. Parasite colonies display both positive and negative chemotactic responses, indicating the ability to detect and react to diffusible signals. Different parasite strains display marked mutual avoidance between neighboring colonies, highlighting specific recognition mechanisms. Furthermore, we show that T. vaginalis is strongly attracted to acidic environments, revealing a niche-adapted pH taxis. Given that vaginal bacteria critically shape local pH, we examined parasite responses to representative members of the vaginal microbiota. T. vaginalis exhibited preferential chemotactic migration toward Lactobacillus gasseri, a hallmark species of eubiotic community state types (CSTs), over Gardnerella vaginalis, which is associated with dysbiotic CST-IV communities, while showing no detectable attraction to Escherichia coli. This selective migration correlated with a robust chemotactic response to lactic acid, a major metabolite produced by lactobacilli. Additionally, when the parasite is co-cultured with the equal number of L. gasseri and G. vaginalis, T. vaginalis exhibits a clear preferential binding to L. gasseri, as demonstrated by flow cytometry and fluorescent microscopy. We show that co-culture of T. vaginalis with either L. gasseri or G. vaginalis results in enhanced parasite growth only in the presence of L. gasseri. Collectively, these findings reveal pH taxis; bacteria-directed migration and preferential association with Lactobacillus as previously underappreciated behavioral traits of T. vaginalis. Such behaviors may destabilize protective microbial communities and drive the transition toward a CST-IV-type dysbiotic state which is frequently associated with trichomoniasis.

This paper investigates a spatiotemporal predator-prey model that incorporates the Allee effect, the fear effect, prey-taxis, and harvesting within a Beddington-DeAngelis functional framework. The model captures the combined influence of biological interactions, behavioral responses, and harvesting activities on population dynamics in a spatially heterogeneous environment. The global existence, positivity, and boundedness of classical solutions are first established under appropriate parameter conditions. The existence and local stability of homogeneous steady states are then analyzed, and the conditions for diffusion-driven instability are derived to characterize the onset of spatial patterns. Using weakly nonlinear analysis, amplitude equations are developed to describe the modulation of spatial modes near the bifurcation threshold. Numerical investigations are conducted to complement the theoretical analysis: bifurcation diagrams are employed to examine the effects of biological parameters such as the Allee threshold ($ \beta $), fear intensity ($ \gamma $), and conversion efficiency ($ \varepsilon $), while spatiotemporal simulations are performed to visualize different scenarios and demonstrate the impact of prey-taxis on pattern formation and population organization.

Light colour is an important environmental factor influencing animal behaviour and its plasticity. Here, we investigated how developmental exposure to different light colours modulates adult phototaxis and locomotion in Drosophila melanogaster. Parental flies were allowed to mate and oviposit under one of five illumination conditions (white, blue, green, yellow, or red), and their offspring subsequently developed under the same light conditions from egg to eclosion. Using independent cohorts (20∼25 adult males per light condition; n = 231 in total), phototaxis and locomotion were evaluated immediately after adult emergence and again following five days of recovery under white light. Flies developed under colour-filtered lights exhibited wavelength-congruent phototactic preferences, spending more time near the wavelength corresponding to their developmental light environment. In addition, individuals developed under long-wavelength lights (red) displayed significantly higher movement and active speeds than those developed under short-wavelength or white light. Notably, after five days of recovery under white light, both wavelength-specific phototactic preferences and enhanced locomotion were largely diminished, indicating that these effects are plastic and reversible. Together, our results demonstrate that the spectral environment during development can transiently modulate adult behavioural outputs, highlighting the importance of early-life light conditions in modulating adult insect behaviour.

Portulaca oleracea polysaccharides (POPs) are one of the main active components of Portulaca oleracea L. (POL), known for their antioxidant, antitumor, and anti-inflammatory properties. This study explores the alleviating effect and mechanism of POP on lipopolysaccharide (LPS)-induced enteritis in young rabbits. By evaluation of the growth performance and meat quality, the optimal concentration of POP was determined to be 50 mg/kg, which can increase the pH value of rabbit meat and extend its shelf life without affecting growth. Through comprehensive transcriptome and untargeted metabolomic analysis, it was found that POP may affect bacterial chemotaxis pathways by regulating genes such as ISG15, reducing the l-aspartic acid content, and thereby regulating the abundance of S24-7 bacteria in the gut, enhancing anti-inflammatory ability. The results indicate that POP can alleviate intestinal inflammation through the gut microbiota metabolite gene interaction network, providing a basis for the development of green feed additives.

Chemotaxis enables eukaryotic cells to detect and migrate along extracellular chemoattractant gradients spanning several orders of magnitude. This remarkable dynamic range relies on adaptation, a process that allows cells to reset their signaling machinery while preserving sensitivity to incremental changes in stimulus intensity. Although numerous actin-dependent feedback mechanisms have been characterized, the molecular basis of adaptation within an actin-independent core gradient-sensing module remains poorly understood. Here, we identify the Ras GTPase-activating protein, C2GAP1, as a critical F-actin-independent effector of the heterotrimeric G protein, Gα2, in Dictyostelium discoideum. Using cytoskeleton-free gradient-sensing cells, quantitative imaging, biochemical assays, FRET-based G-protein activation measurements, and structural modeling, we demonstrate that C2GAP1 controls concentration-dependent adaptation during gradient sensing. Mechanistically, C2GAP1 directly associates with Gα2 in both GDP- and GTP-bound states, with preferential binding to activated Gα2, thereby sustaining membrane recruitment and locally attenuating Ras and downstream signaling. Loss of C2GAP1 enhances G-protein activation, disrupts local inhibition, and impairs rapid reorientation in dynamic gradients. These findings define a direct coupling between heterotrimeric G proteins and the RasGAP, C2GAP1, as a core adaptive module that enables gradient sensing across a wide concentration range.

Dimethyl itaconate (DMI), a permeable derivative of the immunoregulatory metabolite itaconate, exhibits potent anti-inflammatory and antioxidant properties. Its role in osteoarthritis (OA), however, remains unclear. This study demonstrates that DMI attenuates OA progression by suppressing inflammation and macrophage recruitment. In vitro, DMI mitigated IL-1β-induced inflammatory responses, cartilage matrix degradation, and NF-κB/NLRP3 pathway activation in chondrocytes. Transcriptomic analysis revealed the involvement of Toll-like receptor signaling, and functional validation identified TLR2 as a key upstream target. DMI also inhibited IL-1β-induced macrophage migration. In a rat OA model, DMI treatment alleviated cartilage destruction, synovial macrophage infiltration, and TLR2/NF-κB/NLRP3 pathway activation. These findings indicate that DMI ameliorates OA by modulating the joint microenvironment via inhibiting chondrocyte pyroptosis and macrophage chemotaxis, highlighting its potential as a novel therapeutic candidate for OA.

Guiding synthetic nanomaterials toward specific cells and subcellular organelles remains a critical challenge for targeted therapeutics. Here, we report that ATPase-functionalized nanoparticles harness enzymatic turnover to autonomously navigate extracellular and intracellular ATP gradients, accumulating near cell surfaces, experiencing enhanced uptake, and once endocytosed, localizing selectively to mitochondria in both primary human aortic endothelial cells and HeLa cells. ATP depletion or ATPase inhibition abolishes accumulation and disrupts mitochondrial targeting, confirming the requirement for active enzymatic turnover. This targeting mechanism is preserved across particle types, including lipid-based vesicles, indicating broad applicability. This work establishes enzyme-powered chemotaxis as a route to pericellular accumulation, enhanced endocytosis, and organelle-specific delivery, providing a foundation for responsive nanomedicines targeting metabolically active disease environments. The strategy shifts the paradigm from passive, receptor-based delivery to dynamic, energy-responsive targeting.

Sensory rhodopsins (SRs) in haloarchaea form complexes with their cognate transducers (Htrs) to produce wavelength-specific phototactic responses, yet similar architectures mediate distinct behaviors: SRI mediates attraction, SRII drives repulsion, whereas SRM modulates both responses. Until now, structural insight was limited to the Natronomonas pharaonis SRII-HtrII system in a truncated form, without a full-length counterpart for comparison. Moreover, NpHtrII is distinct among HtrII transducers in lacking the large periplasmic domain retained in homologs from Halobacterium salinarum, Haloarcula marismortui and Haloarcula taiwanensis, leaving the canonical SR-Htr architecture unknown. Here, we report the cryo-EM structure of the Haloarcula taiwanensis SRI-HtrI complex, providing a near native, non-crystallized view of a full-length SR-Htr dimer with the cytoplasmic HAMP1 domain resolved. The structure reveals the intact homodimeric receptor-transducer assembly and visualizes the interface between the helix G (Arg215), SRI E-F loop (Pro154), and HtrI HAMP1. These findings fill the long-standing structural gap for a canonical SR-Htr complex and establish a framework for conserved receptor-transducer coupling across archaeal phototaxis systems.

Chemotaxis receptor complexes sense chemical gradient in the cellular environment to direct swimming towards favorable environments. The core signaling units of these complexes are made up of two trimers-of-dimers of chemoreceptors, two CheW and a CheA dimer, which further assemble into large hexagonal signaling arrays. Structural and biochemical studies have provided important information on the architecture and interfaces of these complexes. However, the signaling pathway of these complexes that controls the kinase is not fully understood. In this review, we highlight the highest resolution models of this system and examine the current consensus on the protein-protein interfaces based on models and interface experiments. We also highlight differences observed between signaling states for the individual proteins and the protein interfaces that are proposed to be part of the signaling mechanism. Overall, we conclude that there is strong structural consensus for the protein interfaces but, despite some intriguing results, more information is needed to understand how the interfaces change between signaling states and the role they play in signaling. An animated Interactive 3D Complement (I3DC) is available in Proteopedia at https://proteopedia.org/w/Journal:FEMS_Microbiology_Reviews:1.

Animals employ different strategies for relating sensory input and behavioral output to navigate sensory environments, but what strategy to use, when to switch and why remain unclear. Caenorhabditis elegans navigate by combining "steering" (small heading changes) with "turn" (large reorientations). It is unknown whether transitions between these elements are driven solely by sensory input or also by persistent internal states. It is also unclear how worms sometimes appear to exit turns such that they are already oriented toward a goal, despite their presumed lack of spatial awareness during turns. We address these questions with measurements of sensory-guided navigation and a statistical model of state-dependent control. Worm navigation is well described by a sensory-driven, two-state-switching model whose states persist for seconds and produce distinct sensorimotor mixtures: one state is steer-enriched, the other turn-enriched. This hierarchical temporal organization challenges the view that gradient-climbing strategies are static and purely stimulus-locked. Instead, sensory input causally modulates transitions between persistent states, creating the appearance of "directed turns" when exiting the turn-enriched state. Measurements using genetically perturbed animals and modeling with data-constrained reinforcement-learning both show that state switching enhances gradient-climbing performance. Together, measurement, perturbation, and modeling reveal that state switching is functionally beneficial, organizing behavior across time-a principle that may generalize across species and contexts.