The surprisingly diverse ways that prokaryotes move

VmsR, a LuxR-Type Regulator, Contributes to Virulence, Cell Motility, Extracellular Polysaccharide Production and Biofilm Formation in Xanthomonas oryzae pv. oryzicola

LuxR-type regulators play pivotal roles in regulating numerous bacterial processes, including bacterial motility and virulence, thereby exerting a significant influence on bacterial behavior and pathogenicity. Xanthomonas oryzae pv. oryzicola, a rice pathogen, causes bacterial leaf streak. Our research has identified VmsR, which is a response regulator of the two-component system (TCS) that belongs to the LuxR family. These findings of the experiment reveal that VmsR plays a crucial role in regulating pathogenicity, motility, biofilm formation, and the production of extracellular polysaccharides (EPSs) in Xoc GX01. Notably, our study shows that the vmsR mutant exhibits a reduced swimming motility but an enhanced swarming motility. Furthermore, this mutant displays decreased virulence while significantly increasing EPS production and biofilm formation. We have uncovered that VmsR directly interacts with the promoter regions of fliC and fliS, promoting their expression. In contrast, VmsR specifically binds to the promoter of gumB, resulting in its downregulation. These findings indicate that the knockout of vmsR has profound effects on virulence, motility, biofilm formation, and EPS production in Xoc GX01, providing insights into the intricate regulatory network of Xoc.

Reassessing the Standard Chemotaxis Framework for Understanding Biased Migration in Helicobacter pylori

Helicobacter pylori infections are a major cause of peptic ulcers and gastric cancers. The development of robust inflammation in response to these flagellated, motile bacteria is correlated with poor prognosis. Chemotaxis plays a crucial role in H. pylori colonization, enabling the bacteria to swim toward favorable chemical environments. Unlike the model species of bacterial chemotaxis, Escherichia coli, H. pylori cells possess polar flagella. They run forward by rotating their flagella counterclockwise, whereas backward runs are achieved by rotating their flagella clockwise. We delve into the implications of certain features of the canonical model of chemotaxis on our understanding of biased migration in polarly flagellated bacteria such as H. pylori. In particular, we predict how the translational displacement of H. pylori cells during a backward run could give rise to chemotaxis errors within the canonical framework. Also, H. pylori lack key chemotaxis enzymes found in E. coli, without which sensitive detection of ligands with a wide dynamic range seems unlikely. Despite these problems, H. pylori exhibit robust ability to migrate toward urea-rich sources. We emphasize various unresolved questions regarding the biophysical mechanisms of chemotaxis in H. pylori, shedding light on potential directions for future research. Understanding the intricacies of biased migration in H. pylori could offer valuable insights into how pathogens breach various protective barriers in the human host.

Light Control in Microbial Systems

Light is a key environmental component influencing many biological processes, particularly in prokaryotes such as archaea and bacteria. Light control techniques have revolutionized precise manipulation at molecular and cellular levels in recent years. Bacteria, with adaptability and genetic tractability, are promising candidates for light control studies. This review investigates the mechanisms underlying light activation in bacteria and discusses recent advancements focusing on light control methods and techniques for controlling bacteria. We delve into the mechanisms by which bacteria sense and transduce light signals, including engineered photoreceptors and light-sensitive actuators, and various strategies employed to modulate gene expression, protein function, and bacterial motility. Furthermore, we highlight recent developments in light-integrated methods of controlling microbial responses, such as upconversion nanoparticles and optical tweezers, which can enhance the spatial and temporal control of bacteria and open new horizons for biomedical applications.

Transition from active motion to anomalous diffusion for Bacillus subtilis confined in hydrogel matrices

We investigate the motility of B. subtilis under different degrees of confinement induced by transparent porous hydrogels. The dynamical behavior of the bacteria at short times is linked to characteristic parameters describing the hydrogel porosity. Mean squared displacements (MSDs) reveal that the run-and-tumble dynamics of unconfined B. subtilis progressively turns into sub-diffusive motion with increasing confinement. Correspondingly, the median instantaneous velocity of bacteria decreases and becomes more narrowly distributed, while the reorientation rate increases and reaches a plateau value. Analyzing single-trajectories, we show that the average dynamical behavior is the result of complex displacements, in which active, diffusive and sub-diffusive segments coexist. For small and moderate confinements, the number of active segments reduces, while the diffusive and sub-diffusive segments increase. The alternation of sub-diffusion, diffusion and active motion along the same trajectory can be described as a hopping ad trapping motion, in which hopping events correspond to displacements with an instantaneous velocity exceeding the corresponding mean value along a trajectory. Different from previous observations, escape from local trapping occurs for B. subtilis through active runs but also diffusion. Interestingly, the contribution of diffusion is maximum at intermediate confinements. At sufficiently long times transport coefficients estimated from the experimental MSDs under different degrees of confinement can be reproduced using a recently proposed hopping and trapping model. Finally, we propose a quantitative relationship linking the median velocity of confined and unconfined bacteria through the characteristic confinement length of the hydrogel matrix. Our work provides new insights for the bacterial motility in complex media that mimic natural environments and are relevant to important problems like sterilization, water purification, biofilm formation, membrane permeation and bacteria separation.

Molecular and Phenotypic Investigation on Antibacterial Activities of Limonene Isomers and Its Oxidation Derivative against Xanthomonas oryzae pv. oryzae

Xanthomonas oryzae pv. oryzae (Xoo) causes a devastating bacterial leaf blight in rice. Here, the antimicrobial effects of D-limonene, L-limonene, and its oxidative derivative carveol against Xoo were investigated. We revealed that carveol treatment at ≥ 0.1 mM in liquid culture resulted in significant decrease in Xoo growth rate (> 40%) in a concentration-dependent manner, and over 1 mM, no growth was observed. The treatment with D-limonene and L-limonene also inhibited the Xoo growth but to a lesser extent compared to carveol. These results were further elaborated with the assays of motility, biofilm formation and xanthomonadin production. The carveol treatment over 1 mM caused no motilities, basal level of biofilm formation (< 10%), and significantly reduced xanthomonadin production. The biofilm formation after the treatment with two limonene isomers was decreased in a concentration-dependent manner, but the degree of the effect was not comparable to carveol. In addition, there was negligible effect on the xanthomonadin production mediated by the treatment of two limonene isomers. Field emission-scanning electron microscope (FE-SEM) unveiled that all three compounds used in this study cause severe ultrastructural morphological changes in Xoo cells, showing shrinking, shriveling, and holes on their surface. Moreover, quantitative real-time PCR revealed that carveol and D-limonene treatment significantly down-regulated the expression levels of genes involved in virulence and biofilm formation of Xoo, but not with L-limonene. Together, we suggest that limonenes and carveol will be the candidates of interest in the development of biological pesticides.

A new understanding on the prerequisite of antibiotic biodegradation in wastewater treatment: Adhesive behavior between antibiotic-degrading bacteria and ciprofloxacin

The extensive exploration of antibiotic biodegradation by antibiotic-degrading bacteria in biological wastewater treatment processes has left a notable gap in understanding the behavior of these bacteria when exposed to antibiotics and the initiation of biodegradation processes. This study, therefore, delves into the adhesive behavior of Paraclostridium bifermentans, isolated from a bioreactor treating ciprofloxacin-laden wastewater, towards ciprofloxacin molecules. For the first time, this behavior is observed and characterized through quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy. The investigation further extends to identify key regulatory factors and mechanisms governing this adhesive behavior through a comparative proteomics analysis. The results reveal the dominance of extracellular proteins, particularly those involved in nucleotide binding, hydrolase, and transferase, in the adhesion process. These proteins play pivotal roles through direct chemical binding and the regulation of signaling molecule. Furthermore, QCM-D measurements provide evidence that transferase-related signaling molecules, especially tyrosine, augment the binding between ciprofloxacin and transferases, resulting in enhance ciprofloxacin removal by P. bifermentans (increased by ∼1.2-fold). This suggests a role for transferase-related signaling molecules in manipulating the adhesive behavior of P. bifermentans towards ciprofloxacin. These findings contribute to a new understanding of the prerequisites for antibiotic biodegradation and offer potential strategies for improving the application of antibiotic-degrading bacteria in the treatment of antibiotics-laden wastewater.

Nitrogen Fertilizers Affect Microbial Hitchhiking to the Plant Roots

The phenomenon of microbial hitchhiking, where nonmotile microbes utilize transspecies motility to navigate within their environment, has been observed. However, the underlying factors driving microbial hitchhiking remain unclear. Our study explored how nitrogen fertilizers affect microbial hitchhiking in soil through an in situ planting experiment. We established twelve treatments encompassing the presence and absence of plants, the presence and absence of a filter membrane that is used to prevent hitchhiking, and three nitrogen levels. Results showed that nitrogen influenced bacterial diversity in all soils, an effect thwarted by filter membranes. In the presence of plants, nitrogen significantly affected the bacterial mobility, Bacillus abundance, and plant biomass, but these effects vanished when filters were used. The correlation between motile Bacillus and rhizosphere bacteria was strong without filters at the proper nitrogen levels but weakened with membrane treatments. Thus, plants and nitrogen together, not nitrogen alone, alter the soil microbiome via hitchhiking.

Self-propelled motion controlled by ionic liquids

We studied the self-propulsion of a camphor disk floating on a water surface using two types of ionic liquids (hexylammonium-trifluoroacetate (HHexam-TFA) and hexylethylenediaminium-trifluoroacetate (HHexen-TFA)). Bifurcation between continuous, oscillatory, and no motion was observed depending on the concentration of the ionic liquid. The bifurcation concentration between oscillatory and no motion for HHexam-TFA was lower than that for HHexen-TFA. The different bifurcation concentrations are discussed in relation to the surface tension and Fourier transform infrared spectra of the mixtures of camphor and ionic liquids. These results suggest that the interaction between the ionic liquid molecules at the air/water interface is weakened by the addition of camphor molecules and the features of self-propulsion vary due to the change in the driving force.

Life at the borderlands: microbiomes of interfaces critical to One Health

Microbiomes are foundational components of the environment that provide essential services relating to food security, carbon sequestration, human health, and the overall well-being of ecosystems. Microbiota exert their effects primarily through complex interactions at interfaces with their plant, animal, and human hosts, as well as within the soil environment. This review aims to explore the ecological, evolutionary, and molecular processes governing the establishment and function of microbiome-host relationships, specifically at interfaces critical to One Health-a transdisciplinary framework that recognizes that the health outcomes of people, animals, plants, and the environment are tightly interconnected. Within the context of One Health, the core principles underpinning microbiome assembly will be discussed in detail, including biofilm formation, microbial recruitment strategies, mechanisms of microbial attachment, community succession, and the effect these processes have on host function and health. Finally, this review will catalogue recent advances in microbiology and microbial ecology methods that can be used to profile microbial interfaces, with particular attention to multi-omic, advanced imaging, and modelling approaches. These technologies are essential for delineating the general and specific principles governing microbiome assembly and functions, mapping microbial interconnectivity across varying spatial and temporal scales, and for the establishment of predictive frameworks that will guide the development of targeted microbiome-interventions to deliver One Health outcomes.

The effects of 6 wk of resistance training on the gut microbiome and cardiometabolic health in young adults with overweight and obesity

Obesity is a known risk factor for the development of insulin resistance and other cardiometabolic disorders. Recently, the gut microbiome has been associated with obesity and subsequent health complications. Exercise has been regularly utilized as a therapeutic intervention to treat obesity and its associated comorbidities. This study examined the effects of a 6-wk resistance training exercise program (RT) on the diversity, composition, and metabolic pathways of the gut microbiome. Sedentary young adults (age 18-35 yr) with overweight and obesity (BMI 25-45 kg/m2) were recruited to participate in this randomized controlled trial. Participants were randomized to RT (n = 16), a 6-wk resistance training program (3 days/wk), or control (CT) (n = 16), a nonexercising control. Main outcomes of the study included gut microbiome measures (taxa abundances, diversity, and predicted function) and cardiometabolic outcomes [blood pressure (BP) and glucoregulation]. Increased abundances of Roseburia, a short-chain fatty acid (SCFA) producer were observed over 6 wk (W6) with RT compared with CT (group × week, P < 0.05, q < 0.25). RT also induced marginal alterations in predicted microbial metabolic and cell motility pathways compared with CT (group × week, P < 0.05, q < 0.25). However, RT did not significantly impact overall microbial diversity. Furthermore, RT resulted in higher quantitative insulin-sensitivity check index (QUICKI) and lower diastolic BP at W6 compared with CT [baseline (BL)-adjusted P < 0.05]. RT had mixed effects on the gut microbiome. Although RT increased abundances of Roseburia and induced minor changes in microbial pathways, it is important to consider these changes in the context of the overall stability observed in the microbiome composition.NEW & NOTEWORTHY Resistance training induces mixed changes in the gut microbiome, including an increase in the abundances of the Roseburia genus and minor alterations in microbial pathways. However, it is vital to interpret these changes in light of the broader context, where we observe stability in the overall microbiome composition. This stability may be attributed to the microbiome's resilience, demonstrating its capacity to withstand short-term physiological stressors.

Migration of surface-associated microbial communities in spaceflight habitats

Astronauts are spending longer periods locked up in ships or stations for scientific and exploration spatial missions. The International Space Station (ISS) has been inhabited continuously for more than 20 years and the duration of space stays by crews could lengthen with the objectives of human presence on the moon and Mars. If the environment of these space habitats is designed for the comfort of astronauts, it is also conducive to other forms of life such as embarked microorganisms. The latter, most often associated with surfaces in the form of biofilm, have been implicated in significant degradation of the functionality of pieces of equipment in space habitats. The most recent research suggests that microgravity could increase the persistence, resistance and virulence of pathogenic microorganisms detected in these communities, endangering the health of astronauts and potentially jeopardizing long-duration manned missions. In this review, we describe the mechanisms and dynamics of installation and propagation of these microbial communities associated with surfaces (spatial migration), as well as long-term processes of adaptation and evolution in these extreme environments (phenotypic and genetic migration), with special reference to human health. We also discuss the means of control envisaged to allow a lasting cohabitation between these vibrant microscopic passengers and the astronauts.

Motility mediates satellite formation in confined biofilms

Bacteria have spectacular survival capabilities and can spread in many, vastly different environments. For instance, when pathogenic bacteria infect a host, they expand by proliferation and squeezing through narrow pores and elastic matrices. However, the exact role of surface structures-important for biofilm formation and motility-and matrix density in colony expansion and morphogenesis is still largely unknown. Using confocal laser-scanning microscopy, we show how satellite colonies emerge around Escherichia coli colonies embedded in semi-dense hydrogel in controlled in vitro assays. Using knock-out mutants, we tested how extra-cellular structures, (e.g., exo-polysaccharides, flagella, and fimbria) control this morphology. Moreover, we identify the extra-cellular matrix' density, where this morphology is possible. When paralleled with mathematical modelling, our results suggest that satellite formation allows bacterial communities to spread faster. We anticipate that this strategy is important to speed up expansion in various environments, while retaining the close interactions and protection provided by the community.

Flagellar motor remodeling during swarming requires FliL

FliL is an essential component of the flagellar machinery in some bacteria, but a conditional one in others. The conditional role is for optimal swarming in some bacteria. During swarming, physical forces associated with movement on a surface are expected to exert a higher load on the flagellum, requiring more motor torque to move. FliL was reported to enhance motor output in several bacteria and observed to assemble as a ring around ion-conducting stators that power the motor. In this study we identify a common new function for FliL in diverse bacteria-Escherichia coli, Bacillus subtilis, and Proteus mirabilis. During swarming, all these bacteria show increased cell speed and a skewed motor bias that suppresses cell tumbling. We demonstrate that these altered motor parameters, or "motor remodeling," require FliL. Both swarming and motor remodeling can be restored in an E. coli fliL mutant by complementation with fliL genes from P. mirabilis and B. subtilis, showing conservation of a swarming-associated FliL function across phyla. In addition, we demonstrate that the strong interaction we reported earlier between FliL and the flagellar MS-ring protein FliF is confined to the RBM-3 domain of FliF that links the periplasmic rod to the cytoplasmic C-ring. This interaction may explain several phenotypes associated with the absence of FliL.

Motility of Synthetic Cells from Engineered Lipids

Synthetic cells are artificial systems that resemble natural cells. Significant efforts have been made over the years to construct synthetic protocells that can mimic biological mechanisms and perform various complex processes. These include compartmentalization, metabolism, energy supply, communication, and gene reproduction. Cell motility is also of great importance, as nature uses elegant mechanisms for intracellular trafficking, immune response, and embryogenesis. In this review, we discuss the motility of synthetic cells made from lipid vesicles and relevant molecular mechanisms. Synthetic cell motion may be classified into surface-based or solution-based depending on whether it involves interactions with surfaces or movement in fluids. Collective migration behaviors have also been demonstrated. The swarm motion requires additional mechanisms for intercellular signaling and directional motility that enable communication and coordination among the synthetic vesicles. In addition, intracellular trafficking for molecular transport has been reconstituted in minimal cells with the help of DNA nanotechnology. These efforts demonstrate synthetic cells that can move, detect, respond, and interact. We envision that new developments in protocell motility will enhance our understanding of biological processes and be instrumental in bioengineering and therapeutic applications.

Tracking bacteria at high density with FAST, the Feature-Assisted Segmenter/Tracker

Most bacteria live attached to surfaces in densely-packed communities. While new experimental and imaging techniques are beginning to provide a window on the complex processes that play out in these communities, resolving the behaviour of individual cells through time and space remains a major challenge. Although a number of different software solutions have been developed to track microorganisms, these typically require users either to tune a large number of parameters or to groundtruth a large volume of imaging data to train a deep learning model-both manual processes which can be very time consuming for novel experiments. To overcome these limitations, we have developed FAST, the Feature-Assisted Segmenter/Tracker, which uses unsupervised machine learning to optimise tracking while maintaining ease of use. Our approach, rooted in information theory, largely eliminates the need for users to iteratively adjust parameters manually and make qualitative assessments of the resulting cell trajectories. Instead, FAST measures multiple distinguishing 'features' for each cell and then autonomously quantifies the amount of unique information each feature provides. We then use these measurements to determine how data from different features should be combined to minimize tracking errors. Comparing our algorithm with a naïve approach that uses cell position alone revealed that FAST produced 4 to 10 fold fewer tracking errors. The modular design of FAST combines our novel tracking method with tools for segmentation, extensive data visualisation, lineage assignment, and manual track correction. It is also highly extensible, allowing users to extract custom information from images and seamlessly integrate it into downstream analyses. FAST therefore enables high-throughput, data-rich analyses with minimal user input. It has been released for use either in Matlab or as a compiled stand-alone application, and is available at https://bit.ly/3vovDHn, along with extensive tutorials and detailed documentation.

The Facile Synthesis of Eco-Friendly Zinc Magnesium Bimetal Nanoparticles and its Application in the Eradication of Xanthomonas oryzae pv. oryzae that Causes Leaf Blight Disease of Rice

In this research work, we formulated and successfully assessed the antibacterial capability of zinc magnesium bimetal nanoparticles (ZnMgNPs) against Xanthomonas oryzae pv. oryzae (Xoo), the pathogenic microorganism responsible for causing the destructive leaf blight disease in rice. Successful preparation of ZnMgNPs were determined by UV-vis spectroscopy, EDX (Energy dispersive X-ray), FTIR (Fourier transform infrared) and SEM (Scanning Electron Microscopy). ZnMgNPs had antibacterial efficacy towards Xoo at MIC (minimum inhibitory concentration) 50 µg/ml. ZnMgNPs impeded the formation of biofilm of Xoo by drastically reducing the amount of EPS (extracellular polymeric substances) production and number of sessile cells. The ZnMgNPs also reduced several pathogenic traits of Xoo like motility, xanthomonadin and exoenzymes production. ZnMgNPs target cell membrane of Xoo and also induced oxidative damage as mechanisms of its antibacterial activity. As revealed by an ex-vivo study, ZnMgNPs diminished BLB (bacterial leaf blight) disease symptoms in rice leaves, ZnMgNPs had no effect on rice seed germination, and that following foliar application, the length and biomass of roots and shoots of rice seedling were unaffected, low cytotoxic to A549 cell line showing that ZnMgNPs are non-toxic. However, with ZnMgNPs treatment, the chlorophyll content index (CCI) increased significantly, indicating a good impact on rice physiology. All of these findings suggest that ZnMgNPs could be applied in agriculture to combat the Xoo-caused BLB disease.

Flagellar motor remodeling during swarming requires FliL

FliL is an essential component of the flagellar machinery in some bacteria, but a conditional one in others. The conditional role is for optimal swarming in some bacteria. During swarming, physical forces associated with movement on a surface are expected to exert a higher load on the flagellum, requiring more motor torque to move. Bacterial physiology and morphology are also altered during swarming to cope with the challenges of surface navigation. FliL was reported to enhance motor output in several bacteria and observed to assemble as a ring around ion-conducting stators that power the motor. In this study we identify a common new function for FliL in diverse bacteria - Escherichia coli, Bacillus subtilis and Proteus mirabilis . During swarming, all these bacteria show increased cell speed and a skewed motor bias that suppresses cell tumbling. We demonstrate that these altered motor parameters, or 'motor remodeling', require FliL. Both swarming and motor remodeling can be restored in an E. coli fliL mutant by complementation with fliL genes from P. mirabilis and B. subtilis , showing conservation of swarming-associated FliL function across phyla. In addition, we demonstrate that the strong interaction we reported earlier between FliL and the flagellar MS-ring protein FliF is confined to the RBM-3 domain of FliF that links the periplasmic rod to the cytoplasmic C-ring. This interaction may explain several phenotypes associated with the absence of FliL.

Phylogenomics of the Liquorilactobacillus Genus

The genus Liquorilactobacillus is a new genus commonly found in wine and plants. Despite its significance, previous studies on Liquorilactobacillus are primarily focused on phenotypic experiments, with limited genome-level studies. This study used comparative genomics to analyze 24 genomes from the genus Liquorilactobacillus, including two novel sequenced strains (IMAU80559 and IMAU80777). A phylogenetic tree of 24 strains was constructed based on 122 core genes and divided into two clades, A and B. Significant differences in GC content were observed between the two clades (P = 10e^-4). Additionally, change revealed to suggests that clade B has more exposure to prophage infection having an upgraded immune system. Further analysis of functional annotation and selective pressure suggests that clade A was subjected to greater selection pressure than B clade (P = 3.9e^-6) and had higher number of functional types annotated than clade B (P = 2.7e^-3), while clade B had a lower number of pseudogenes than clade A (P = 1.9e^-2). The findings suggest that differently prophages and environmental stress may have influenced the common ancestor of clades A and B during evolution, leading to the development of two distinct clades.

Genomic and phenotypic insight into Xanthomonas vesicatoria strains with different aggressiveness on tomato

Xanthomonas vesicatoria is one of the causal agents of bacterial spot, a disease that seriously affects the production of tomato (Solanum lycopersicum) and pepper (Capsicum annum) worldwide. In Argentina, bacterial spot is found in all tomato producing areas, with X. vesicatoria being one of the main species detected in the fields. Previously, we isolated three X. vesicatoria strains BNM 208, BNM 214, and BNM 216 from tomato plants with bacterial spot, and found they differed in their ability to form biofilm and in their degree of aggressiveness. Here, the likely causes of those differences were explored through genotypic and phenotypic studies. The genomes of the three strains were sequenced and assembled, and then compared with each other and also with 12 other publicly available X. vesicatoria genomes. Phenotypic characteristics (mainly linked to biofilm formation and virulence) were studied in vitro. Our results show that the differences observed earlier between BNM 208, BNM 214, and BNM 216 may be related to the structural characteristics of the xanthan gum produced by each strain, their repertoire of type III effectors (T3Es), the presence of certain genes associated with c-di-GMP metabolism and type IV pili (T4P). These findings on the pathogenicity mechanisms of X. vesicatoria could be useful for developing bacterial spot control strategies aimed at interfering with the infection processes.

Crosstalk between in situ root exudates and rhizobacteria to promote rice growth by selenium nanomaterials

Maximizing the potential of plant-microbe systems offers great opportunities to confront sustainability issues in agroecosystems. However, the dialog between root exudates and rhizobacteria remains largely unknown. As a novel nanofertilizer, nanomaterials (NMs) have significant potential to improve agricultural productivity due to their unique properties. Here, soil amendment with 0.1 mg·kg^-1 selenium (Se) NMs (30-50 nm) significantly promoted rice seedling growth. Differences in root exudates and rhizobacteria were evident. At an earlier time point (3^rd week), Se NMs increased the relative content of malic and citric acid by 15.4- and 8.1-fold, respectively. Meanwhile, the relative abundances of Streptomyces and Sphingomonas were increased by 164.6 % and 38.3 %, respectively. As the exposure time increased, succinic acid (40.5-fold) at the 4^th week and salicylic acid (4.7-fold) and indole-3-acetic (7.0-fold) at the 5^th week were enhanced, while Pseudomonas and Bacillus increased at the 4^th (112.3 % and 50.2 %) and 5^th weeks (190.8 % and 53.1 %), respectively. Further analysis indicated that (1) Se NMs directly enhanced the synthesis and secretion of malic and citric acids by upregulating their biosynthesis and transporter genes and then recruited Bacillus and Pseudomonas; (2) Se NMs upregulated the chemotaxis and flagellar genes of Sphingomonas for more interaction with rice plants, thereby promoting rice growth and stimulating root exudate secretion. This crosstalk of root exudates and rhizobacteria enhanced nutrient uptake, resulting in promoted rice growth. Our study offers insights into the crosstalk between root exudates and rhizobacteria by NMs and provides new insights into rhizosphere regulation in nano-enabled agriculture.

Flagellar polymorphism-dependent bacterial swimming motility in a structured environment

Most motile bacteria use supramolecular motility machinery called bacterial flagellum, which converts the chemical energy gained from ion flux into mechanical rotation. Bacterial cells sense their external environment through a two-component regulatory system consisting of a histidine kinase and response regulator. Combining these systems allows the cells to move toward favorable environments and away from their repellents. A representative example of flagellar motility is run-and-tumble swimming in Escherichia coli, where the counter-clockwise (CCW) rotation of a flagellar bundle propels the cell forward, and the clockwise (CW) rotation undergoes cell re-orientation (tumbling) upon switching the direction of flagellar motor rotation from CCW to CW. In this mini review, we focus on several types of chemotactic behaviors that respond to changes in flagellar shape and direction of rotation. Moreover, our single-cell analysis demonstrated back-and-forth swimming motility of an original E. coli strain. We propose that polymorphic flagellar changes are required to enhance bacterial movement in a structured environment as a colony spread on an agar plate.

Swimming of Buoyant Bacteria in Quiescent Medium and Shear Flows

Gravity has an unavoidable effect on all living organisms inhabiting fluidic surroundings. To investigate the spatial distribution of bacteria in quiescent fluids and their rheotactic behavior in shear flows under buoyancy, we adjust the buoyant force to regulate bacterial swimming in a microfluidic channel. It is found that swimming bacteria of Escherichia coli exhibit an obvious vertical separation when exposed to a medium with high density and gradually gather close to the up wall within minutes. The bacterial population presents a net upward number flux, which enhances the trapping of motile bacteria onto the up surface as a result of buoyancy force apart from the hydrodynamic and kinematic interactions in quiescent fluids. When flow is imposed into the channel, the buoyancy effect is however significantly suppressed. Additionally, the drift velocity perpendicular to the buoyancy vector as a result of chirality-induced transverse swimming decreases with buoyancy force. However, this transverse drift capability is recovered after excluding the intrinsic swimming motility in a quiescent medium. Failing to escape from the trapping as a result of buoyant force allows for a facile separation of bacteria along the vertical direction. The findings also offer a controllable way to redisperse and homogenize the bacteria distribution close to walls by imposing a weak shear flow.

The action of phytochemicals in biofilm control

Covering: 2009 to 2021Antimicrobial resistance is now rising to dangerously high levels in all parts of the world, threatening the treatment of an ever-increasing range of infectious diseases. This has becoming a serious public health problem, especially due to the emergence of multidrug-resistance among clinically important bacterial species and their ability to form biofilms. In addition, current anti-infective therapies have low efficacy in the treatment of biofilm-related infections, leading to recurrence, chronicity, and increased morbidity and mortality. Therefore, it is necessary to search for innovative strategies/antibacterial agents capable of overcoming the limitations of conventional antibiotics. Natural compounds, in particular those obtained from plants, have been exhibiting promising properties in this field. Plant secondary metabolites (phytochemicals) can act as antibiofilm agents through different mechanisms of action from the available antibiotics (inhibition of quorum-sensing, motility, adhesion, and reactive oxygen species production, among others). The combination of different phytochemicals and antibiotics have revealed synergistic or additive effects in biofilm control. This review aims to bring together the most relevant reports on the antibiofilm properties of phytochemicals, as well as insights into their structure and mechanistic action against bacterial pathogens, spanning December 2008 to December 2021.

Cryo-EM structure of gas vesicles for buoyancy-controlled motility

Gas vesicles are gas-filled nanocompartments that allow a diverse group of bacteria and archaea to control their buoyancy. The molecular basis of their properties and assembly remains unclear. Here, we report the 3.2 Å cryo-EM structure of the gas vesicle shell made from the structural protein GvpA that self-assembles into hollow helical cylinders closed off by cone-shaped tips. Two helical half shells connect through a characteristic arrangement of GvpA monomers, suggesting a mechanism of gas vesicle biogenesis. The fold of GvpA features a corrugated wall structure typical for force-bearing thin-walled cylinders. Small pores enable gas molecules to diffuse across the shell, while the exceptionally hydrophobic interior surface effectively repels water. Comparative structural analysis confirms the evolutionary conservation of gas vesicle assemblies and demonstrates molecular features of shell reinforcement by GvpC. Our findings will further research into gas vesicle biology and facilitate molecular engineering of gas vesicles for ultrasound imaging.

Loss of Flagella-Related Genes Enables a Nonflagellated, Fungal-Predating Bacterium To Strengthen the Synthesis of an Antifungal Weapon

Loss of flagellar genes causes a nonmotile phenotype. The genus Lysobacter consists of numerous environmentally ubiquitous, nonflagellated bacteria, including Lysobacter enzymogenes, an antifungal bacterium that is beneficial to plants. L. enzymogenes still has many flagellar genes on its genome, although this bacterium does not engage in flagella-driven motility. Here, we report that loss of certain flagellar genes allows L. enzymogenes to strengthen its evolutionarily gained capacity in fungal killing. To clarify why this bacterium loses flagellar genes during the evolutionary process, we cloned several representative flagellar genes from Xanthomonas oryzae, a flagellated, phylogenetically related species of Lysobacter, and introduced them individually into L. enzymogenes to mimic genomic reacquisition of lost flagellar genes. Heterogeneous expression of the three X. oryzae flagellar structural genes (Xo-motA, Xo-motB, Xo-fliE) and one flagellar regulatory gene (Xo-fleQ) remarkably weakened the bacterial capacity to kill fungal pathogens by impairing the synthesis of an antifungal weapon, known as the heat-stable antifungal factor (HSAF). We further investigated the underlying mechanism by selecting Xo-FleQ as the representative because it is a master transcription factor responsible for flagellar gene expression. Xo-FleQ inhibited the transcription of operon genes responsible for HSAF synthesis via direct binding of Xo-FleQ to the promoter region, thereby decreasing HSAF biosynthesis by L. enzymogenes. These observations suggest a possible genome and function coevolution event, in which an antifungal bacterium deletes certain flagellar genes in order to enhance its ability to kill fungi. IMPORTANCE It is generally recognized that flagellar genes are commonly responsible for the flagella-driven bacterial motility. Thus, finding nonflagellated bacteria partially or fully lost flagellar genes is not a surprise. However, the present study provides new insights into this common idea. We found that loss of either certain flagellar structural or regulatory genes (such as motA, motB, fliE, and fleQ) allows a nonflagellated, antifungal bacterium (L. enzymogenes) to stimulate its fungal-killing capacity, outlining a genome-function coevolution event, where an antifungal bacterium "smartly" designed its genome to "delete" crucial flagellar genes to coordinate flagellar loss and fungal predation. This unusual finding might trigger bacteriologists to reconsider previously ignored functions of the lost flagellar genes in any nonflagellated, pathogenic, or beneficial bacteria.

Complete functional analysis of type IV pilus components of a reemergent plant pathogen reveals neofunctionalization of paralog genes

Type IV pilus (TFP) is a multifunctional bacterial structure involved in twitching motility, adhesion, biofilm formation, as well as natural competence. Here, by site-directed mutagenesis and functional analysis, we determined the phenotype conferred by each of the 38 genes known to be required for TFP biosynthesis and regulation in the reemergent plant pathogenic fastidious prokaryote Xylella fastidiosa. This pathogen infects > 650 plant species and causes devastating diseases worldwide in olives, grapes, blueberries, and almonds, among others. This xylem-limited, insect-transmitted pathogen lives constantly under flow conditions and therefore is highly dependent on TFP for host colonization. In addition, TFP-mediated natural transformation is a process that impacts genomic diversity and environmental fitness. Phenotypic characterization of the mutants showed that ten genes were essential for both movement and natural competence. Interestingly, seven sets of paralogs exist, and mutations showed opposing phenotypes, indicating evolutionary neofunctionalization of subunits within TFP. The minor pilin FimT3 was the only protein exclusively required for natural competence. By combining approaches of molecular microbiology, structural biology, and biochemistry, we determined that the minor pilin FimT3 (but not the other two FimT paralogs) is the DNA receptor in TFP of X. fastidiosa and constitutes an example of neofunctionalization. FimT3 is conserved among X. fastidiosa strains and binds DNA non-specifically via an electropositive surface identified by homolog modeling. This protein surface includes two arginine residues that were exchanged with alanine and shown to be involved in DNA binding. Among plant pathogens, fimT3 was found in ~ 10% of the available genomes of the plant associated Xanthomonadaceae family, which are yet to be assessed for natural competence (besides X. fastidiosa). Overall, we highlight here the complex regulation of TFP in X. fastidiosa, providing a blueprint to understand TFP in other bacteria living under flow conditions.

Transposon mutagenesis and genome sequencing identify two novel, tandem genes involved in the colony spreading of Flavobacterium collinsii, isolated from an ayu fish, Plecoglossus altivelis

Bacteria of the family Flavobacteriaceae (flavobacteria) primarily comprise nonpathogenic bacteria that inhabit soil and water (both marine and freshwater). However, some bacterial species in the family, including Flavobacterium psychrophilum and Flavobacterium columnare, are known to be pathogenic to fish. Flavobacteria, including the abovementioned pathogenic bacteria, belong to the phylum Bacteroidota and possess two phylum-specific features, gliding motility and a protein secretion system, which are energized by a common motor complex. Herein, we focused on Flavobacterium collinsii (GiFuPREF103) isolated from a diseased fish (Plecoglossus altivelis). Genomic analysis of F. collinsii GiFuPREF103 revealed the presence of a type IX secretion system and additional genes associated with gliding motility and spreading. Using transposon mutagenesis, we isolated two mutants with altered colony morphology and colony spreading ability; these mutants had transposon insertions in pep25 and lbp26. The glycosylation material profiles revealed that these mutants lacked the high-molecular-weight glycosylated materials present in the wild-type strain. In addition, the wild-type strains exhibited fast cell population movement at the edge of the spreading colony, whereas reduced cell population behavior was observed in the pep25- and lbp26-mutant strains. In the aqueous environment, the surface layers of these mutant strains were more hydrophobic, and they formed biofilms with enhanced microcolony growth compared to those with the wild-type. In Flavobacterium johnsoniae, the Fjoh_0352 and Fjoh_0353 mutant strains were generated, which were based on the ortholog genes of pep25 and lbp26. In these F. johnsoniae mutants, as in F. collinsii GiFuPREF103, colonies with diminished spreading capacity were formed. Furthermore, cell population migration was observed at the edge of the colony in wild-type F. johnsoniae, whereas individual cells, and not cell populations, migrated in these mutant strains. The findings of the present study indicate that pep25 and lbp26 contribute to the colony spreading of F. collinsii.

Swarming Motility Assays in Salmonella

Salmonella enterica has six subspecies, of which the subspecies enterica is the most important for human health. The dispersal and infectivity of this species are dependent upon flagella-driven motility. Two kinds of flagella-mediated movements have been described-swimming individually in bulk liquid and swarming collectively over a surface substrate. During swarming, the bacteria acquire a distinct physiology, the most significant consequence of which is acquisition of adaptive resistance to antibiotics. Described here are protocols to cultivate, verify, and study swimming and swarming motility in S. enterica, and an additional "border-crossing" assay, where cells "primed" to swarm are presented with an environmental challenge such as antibiotics to assess their propensity to handle the challenge.

Controlling kinetics of self-propelled rod-like swimmers near multi sinusoidal substrate

Motility is defined as the movement of cells by some form of self-propulsion. Some organisms motile by using long flagella that quickly rotate to propel them over various surfaces (in swarming and swimming mechanism), while few motile without the aid of flagella (in twitching, sliding and gliding mechanism). Among these modes, gliding motility is adopted by a rod-shaped organism famously known as gliding bacteria. It is hypothesized that in such type of motility, organism motile under their own power by secreting a layer of slime on the substrate. In this study, an active wall is considered as a substrate and a two-dimensional wavy sheet as an organism. Slip effects are also employed in the current work. The physical properties of the slime are governed by a suitable constitutive equation of couple stress model. A sixth order BVP is obtained by utilizing lubrication assumption. For an appropriate fixed pair of flow rate and organism speed the BVP is solved by MATLAB built-in function bvp-5c. This solution is utilized in the mechanical equilibrium conditions which are obviously not satisfied yet. To satisfy these conditions, the pair of flow rate and gliding speed is refined by a root finding algorithm (modified Newton-Raphson method). By employing this numerical scheme, various figures are shown to demonstrate the effect of several associated parameters on organism speed, flow rate, energy expended by the glider, streamlines and longitudinal velocity. It is observed from the graphical results that organism speed and energy consumption is directly proportional to the couple stress parameter and slip effects.

Polar flagellar wrapping and lateral flagella jointly contribute to Shewanella putrefaciens environmental spreading

Flagella enable bacteria to actively spread within the environment. A number of species possess two separate flagellar systems, where in most cases a primary polar flagellar system is supported by distinct secondary lateral flagella under appropriate conditions. Using functional fluorescence tagging on one of these species, Shewanella putrefaciens, as a model system, we explored how two different flagellar systems can exhibit efficient joint function. The S. putrefaciens secondary flagellar filaments are composed as a mixture of two highly homologous non-glycosylated flagellins, FlaA₂ and FlaB₂ . Both are solely sufficient to form a functional filament, however, full spreading motility through soft agar requires both flagellins. During swimming, lateral flagella emerge from the cell surface at angles between 30° and 50°, and only filaments located close to the cell pole may form a bundle. Upon a directional shift from forward to backward swimming initiated by the main polar flagellum, the secondary filaments flip over and thus support propulsion into either direction. Lateral flagella do not inhibit the wrapping of the polar flagellum around the cell body at high load. Accordingly, screw thread-like motility mediated by the primary flagellum and activity of lateral flagella cumulatively supports spreading through constricted environments such as polysaccharide matrices.

Mechanisms and models of movement of protocells and bacteria in the early stages of evolution

A review of the physicochemical models of the movement of protocells and bacteria was performed. The mechanisms of gliding and movement based on flagella are considered. Based on the models, the average speed of movement of protocells and bacteria was calculated. A physicochemical model of bacterial gliding was constructed. The efficiency of the process of converting the energy of ATP into the energy of motion is estimated. A review of models of movement with the help of flagella was performed. A model has been constructed for converting ATP energy into proton and sodium motive forces, which, in turn, are converted into energy of rotor rotation. The problem of the accuracy of operation of nanomachines, on the basis of which the directed movement of bacteria occurs, is discussed. The considered models can be applied to create nanomotors for medical purposes.

FliL Differentially Interacts with Two Stator Systems To Regulate Flagellar Motor Output in Pseudomonas aeruginosa

FliL emerged as a modulator of flagellar motor function in several bacterial species, but its function in Pseudomonas aeruginosa was unknown. Here, by performing single-motor studies using a bead assay, we elucidated its effects on the flagellar motor in P. aeruginosa .

Pan-Genome Analysis of Campylobacter: Insights on the Genomic Diversity and Virulence Profile

The genus Campylobacter contains pathogens that cause bacterial gastroenteritis in humans and animals. Despite large-scale sequencing efforts to raise clinical awareness of Campylobacter, little is known about the diversity and functions of virulence factors. Here, we constructed the pan-genome of Campylobacter using 39 representative genomes, elucidating their genetic diversity, evolutionary characteristics, and virulence and resistance profiles. The Campylobacter pan-genome was open and showed extensive genome variability, with high levels of gene expansion and contraction as the organism evolved. These Campylobacter members had diverse virulence gene content, and six potential core virulence genes (porA, PEB4, cheY, htrB, Cj1135, and kpsF) have been identified. The conserved mechanisms for Campylobacter pathogenicity were related to adherence, motility, and immune modulation. We emphasized the relative importance of variable virulence genes. Many virulence genes have experienced expansion or contraction in specific lineages, which may be one of the factors causing differences in the content of virulence genes. Additionally, these Campylobacter genomes have a high prevalence of the cmeA and cmeC genes, which are linked to the CmeABC pump and contribute to multidrug resistance. The genomic variations, core and variable virulence factors, and resistance genes of Campylobacter characterized in this study would contribute to a better understanding of the virulence of Campylobacter and more effective use of candidates for drug development and prevention of Campylobacter infections. IMPORTANCE Pathogenic members of the genus Campylobacter are recognized as one of the major causative agents of human bacterial gastroenteritis. This study revealed the pan-genome of 39 Campylobacter species, provided the most updated reconstruction of the global virulence gene pool of 39 Campylobacter species, and identified species-related virulence differences. This study highlighted the basic conserved functionality and specificity of pathogenicity that are crucial to infection, which was critical for improving the diagnosis and prevention of Campylobacter infections.

Recent advances in bacterial therapeutics based on sense and response

Intelligent drug delivery is a promising strategy for cancer therapies. In recent years, with the rapid development of synthetic biology, some properties of bacteria, such as gene operability, excellent tumor colonization ability, and host-independent structure, make them ideal intelligent drug carriers and have attracted extensive attention. By implanting condition-responsive elements or gene circuits into bacteria, they can synthesize or release drugs by sensing stimuli. Therefore, compared with traditional drug delivery, the usage of bacteria for drug loading has better targeting ability and controllability, and can cope with the complex delivery environment of the body to achieve the intelligent delivery of drugs. This review mainly introduces the development of bacterial-based drug delivery carriers, including mechanisms of bacterial targeting to tumor colonization, gene deletions or mutations, environment-responsive elements, and gene circuits. Meanwhile, we summarize the challenges and prospects faced by bacteria in clinical research, and hope to provide ideas for clinical translation.

The Phloem as an Arena for Plant Pathogens

Although the phloem is a highly specialized tissue, certain pathogens, including phytoplasmas, spiroplasmas, and viruses, have evolved to access and live in this sequestered and protected environment, causing substantial economic harm. In particular, Candidatus Liberibacter spp. are devastating citrus in many parts of the world. Given that most phloem pathogens are vectored, they are not exposed to applied chemicals and are therefore difficult to control. Furthermore, pathogens use the phloem network to escape mounted defenses. Our review summarizes the current knowledge of phloem anatomy, physiology, and biochemistry relevant to phloem/pathogen interactions. We focus on aspects of anatomy specific to pathogen movement, including sieve plate structure and phloem-specific proteins. Phloem sampling techniques are discussed. Finally, pathogens that cause particular harm to the phloem of crop species are considered in detail.

Pathogen Adaptation to the Xylem Environment

A group of aggressive pathogens have evolved to colonize the plant xylem. In this vascular tissue, where water and nutrients are transported from the roots to the rest of the plant, pathogens must be able to thrive under acropetal xylem sap flow and scarcity of nutrients while having direct contact only with predominantly dead cells. Nevertheless, a few bacteria have adapted to exclusively live in the xylem, and various pathogens may colonize other plant niches without causing symptoms unless they reach the xylem. Once established, the pathogens modulate its physicochemical conditions to enhance their growth and virulence. Adaptation to the restrictive lifestyle of the xylem leads to genome reduction in xylem-restricted bacteria, as they have a higher proportion of pseudogenes in their genome. The basis of xylem adaptation is not completely understood; therefore, a need still exists for model systems to advance the knowledge on this topic.

Detection of Atypical Motile Staphylococcus aureus from Rain Floods

Abstract: Heavy rain floods is one of the primary risk factors for human health, and it can significantly regulate microbial communities and enhance the transfer of infections within the affected areas. Recently, the flood crisis is becoming one of the severe natural events in Mosul / Iraq. It may continue for months during which samples of accumulated rainwater were collected. Twelve Staphylococcus aureus were isolated by using two selective media: Mannitol Salt agar and Vogel-Johnson media in addition to Blood agar. An unusual colony spreading which resembles. "Bacillus colonies in twelve Staphylococcus aureus isolates was observed on Mannitol Salt agar and semisolid nutrient agar. Actively motile cocci in single and cluster arrangements that is not characteristic of brownian movement was shown in wet mount microscopic observation Furthermore, biosurfactant detection by oil spreading method ( oil displacement activity) showed that all isolates demonstrated various degrees of surfactant production which has beeen reported. to be responsible for stimulating "colony spreading" phenomenon in S. aureux. Motility can play a crucial role for survival bacterial species by which they get nutrients, avoid toxins and predators, and genetic information exchange by mating. The present study highlights for the first time. Mosul city a motile opportunistic aureus obtained from harvested rainwater samples during high-rainfall periods. Utilization of untreated harvested rainwater could thus offer a significant health threat to consumers, especially children. and immunocompromised individuals.

Shape Memory Alloy Helical Microrobots with Transformable Capability towards Vascular Occlusion Treatment

Practical implementation of minimally invasive biomedical applications has been a long-sought goal for microrobots. In this field, most previous studies only demonstrate microrobots with locomotion ability or performing a single task, unable to be functionalized effectively. Here, we propose a biocompatible shape memory alloy helical microrobot with regulative structure transformation, making it possible to adjust its motion behavior and mechanical properties precisely. Especially, towards vascular occlusion problem, these microrobots reveal a fundamental solution strategy in the mechanical capability using shape memory effect. Such shape-transformable microrobots can not only manipulate thrust and torque by structure to enhance the unclogging efficiency as a microdriller but also utilize the high work energy to apply the expandable helical tail as a self-propulsive stent. The strategy takes advantage of untethered manipulation to operate microsurgery without unnecessary damage. This study opens a route to functionalize microrobots via accurate tuning in structures, motions, and mechanical properties.

Cell shape controls rheotaxis in small parasitic bacteria

Mycoplasmas, a group of small parasitic bacteria, adhere to and move across host cell surfaces. The role of motility across host cell surfaces in pathogenesis remains unclear. Here, we used optical microscopy to visualize rheotactic behavior in three phylogenetically distant species of Mycoplasma using a microfluidic chamber that enabled the application of precisely controlled fluid flow. We show that directional movements against fluid flow occur synchronously with the polarized cell orienting itself to be parallel against the direction of flow. Analysis of depolarized cells revealed that morphology itself functions as a sensor to recognize rheological properties that mimic those found on host-cell surfaces. These results demonstrate the vital role of cell morphology and motility in responding to mechanical forces encountered in the native environment.

The small, parasitic bacterium Mycoplasma pneumoniae attaches to, and moves over, host cell surfaces. Adherence to host surfaces and motility are critical for the pathogenicity of M. pneumoniae. The role of motility by M. pneumoniae in vivo, however, is poorly understood. Host airways generate constant fluid flow toward the mouth as part of their defense against pathogens and irritants. Consequently, pulmonary invaders must counter the rheological forces found in host airways in order to successfully colonize the host. Here, we demonstrate that M. pneumoniae exhibits directional movement against fluid flow. These findings suggest there is a vital role for rheotactic motility that has evolved in order to overcome host defense mechanisms such as mucociliary clearance.

Wrapped Up: The Motility of Polarly Flagellated Bacteria

A huge number of bacterial species are motile by flagella, which allow them to actively move toward favorable environments and away from hazardous areas and to conquer new habitats. The general perception of flagellum-mediated movement and chemotaxis is dominated by the Escherichia coli paradigm, with its peritrichous flagellation and its famous run-and-tumble navigation pattern, which has shaped the view on how bacteria swim and navigate in chemical gradients. However, a significant amount-more likely the majority-of bacterial species exhibit a (bi)polar flagellar localization pattern instead of lateral flagella. Accordingly, these species have evolved very different mechanisms for navigation and chemotaxis. Here, we review the earlier and recent findings on the various modes of motility mediated by polar flagella. Expected final online publication date for the Annual Review of Microbiology, Volume 76 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Motile behaviour of droplets in lipid systems

Motility is the capacity for living organisms to move autonomously and with purpose, and is essential to life. The transition from abiotic chemistry into motile cellular compartments has yet to be understood, but motile behaviour likely followed chemical evolution because primeval cell survival depended on scouting for resources effectively. Minimalistic motile systems provide an experimental framework to delineate the emergence mechanisms of such an evolutionary asset. In this Review, we discuss frontier developments in controlling the movement of droplets in lipid systems, in particular, chemotactic behaviours driven by fluctuations in interfacial tension, because of its simple mechanism and prebiotic relevance. Although most efforts have focused on designing oil droplet motility in lipid-rich aqueous solutions, we highlight that water droplets can also move in lipid-enriched oils. First, we describe how droplets evolve chemotactic motility in lipid systems. Next, we review how these oil droplets can adapt their movement to illumination conditions. Finally, we discuss examples where chemical reactivity brings complexity to motility. This work contributes to systems chemistry, where chemical reactions combined with physicochemical phenomena can yield new functions, such that a limited set of molecules can promote complex movement at larger functional scales by following the rules of molecular chemistry.

Gliding motility of a uranium-tolerant Bacteroidetes bacterium Chryseobacterium sp. strain PMSZPI: insights into the architecture of spreading colonies

Uranium-tolerant soil bacterium Chryseobacterium sp. strain PMSZPI moved over solid agar surfaces by gliding motility thereby forming spreading colonies which is a hallmark of members of Bacteroidetes phylum. PMSZPI genome harboured orthologs of all the gld and spr genes considered as core bacteroidetes gliding motility genes of which gldK, gldL, gldM and gldN were co-transcribed. Here, we present the intriguing interplay between gliding motility and cellular organization in PMSZPI spreading colonies. While nutrient deficiency enhanced colony spreading, high agar concentrations and presence of motility inhibitor like 5-hydroxyindole reduced the spreading. A detailed in situ structural analysis of spreading colonies revealed closely packed cells forming multiple layers at centre of colony while the edges showed clusters of cells periodically arranged in hexagonal lattices interconnected with each other. The cell migration within colony was visualized as branched structures wherein the cells were buried within extracellular matrix. PMSZPI colonies exhibited strong iridescence possibly as a result of periodicity within the cell population achieved through gliding motility. Presence of uranium reduced motility and iridescence and induced biofilm formation. The coordinated study of gliding motility and iridescence apparently influenced by uranium provides unique insights into the lifestyle of PMSZPI residing in uranium enriched environment.

Micro/Nanosystems for Magnetic Targeted Delivery of Bioagents

Targeted delivery of pharmaceuticals is promising for efficient disease treatment and reduction in adverse effects. Nano or microstructured magnetic materials with strong magnetic momentum can be noninvasively controlled via magnetic forces within living beings. These magnetic carriers open perspectives in controlling the delivery of different types of bioagents in humans, including small molecules, nucleic acids, and cells. In the present review, we describe different types of magnetic carriers that can serve as drug delivery platforms, and we show different ways to apply them to magnetic targeted delivery of bioagents. We discuss the magnetic guidance of nano/microsystems or labeled cells upon injection into the systemic circulation or in the tissue; we then highlight emergent applications in tissue engineering, and finally, we show how magnetic targeting can integrate with imaging technologies that serve to assist drug delivery.

Structural insights into the mechanism of archaellar rotational switching

Signal transduction via phosphorylated CheY towards the flagellum and the archaellum involves a conserved mechanism of CheY phosphorylation and subsequent conformational changes within CheY. This mechanism is conserved among bacteria and archaea, despite substantial differences in the composition and architecture of archaellum and flagellum, respectively. Phosphorylated CheY has higher affinity towards the bacterial C-ring and its binding leads to conformational changes in the flagellar motor and subsequent rotational switching of the flagellum. In archaea, the adaptor protein CheF resides at the cytoplasmic face of the archaeal C-ring formed by the proteins ArlCDE and interacts with phosphorylated CheY. While the mechanism of CheY binding to the C-ring is well-studied in bacteria, the role of CheF in archaea remains enigmatic and mechanistic insights are absent. Here, we have determined the atomic structures of CheF alone and in complex with activated CheY by X-ray crystallography. CheF forms an elongated dimer with a twisted architecture. We show that CheY binds to the C-terminal tail domain of CheF leading to slight conformational changes within CheF. Our structural, biochemical and genetic analyses reveal the mechanistic basis for CheY binding to CheF and allow us to propose a model for rotational switching of the archaellum.

Signal transduction via phosphorylated CheY is conserved in bacteria and archaea. In this study, the authors employ structural biochemistry combined with cell biology to delineate the mechanism of CheY recognition by the adaptor protein CheF.

Mechanical limitation of bacterial motility mediated by growing cell chains

Contrasting most known bacterial motility mechanisms, a bacterial sliding motility discovered in at least two Gram-positive bacterial families does not depend on designated motors. Instead, the cells maintain end-to-end connections following cell divisions to form long chains and exploit cell growth and division to push the cells forward. To investigate the dynamics of this motility mechanism, we constructed a mechanical model that depicts the interplay of the forces acting on and between the cells comprising the chain. Due to the exponential growth of individual cells, the tips of the chains can, in principle, accelerate to speeds faster than any known single-cell motility mechanism can achieve. However, analysis of the mechanical model shows that the exponential acceleration comes at the cost of an exponential buildup in mechanical stress in the chain, making overly long chains prone to breakage. Additionally, the mechanical model reveals that the dynamics of the chain expansion hinges on a single non-dimensional parameter. Perturbation analysis of the mechanical model further predicts the critical stress leading to chain breakage and its dependence on the non-dimensional parameter. Finally, we developed a simplistic population expansion model that uses the predicted breaking behavior to estimate the physical limit of chain-mediated population expansion. Predictions from the models provide critical insights into how this motility depends on key physical properties of the cell and the substrate. Overall, our models present a generically applicable theoretical framework for cell chain-mediated bacterial sliding motility and provide guidance for future experimental studies on such motility.

The GDSL-Lipolytic Enzyme Lip1 Is Required for Full Virulence of the Cucurbit Pathogenic Bacterium Acidovorax citrulli

Bacterial fruit blotch caused by Acidovoraxcitrulli is a serious disease of cucurbit crops. Here we report characterization of a mutant strain of A. citrulli M6 defective in lip1, a gene encoding a lipolytic enzyme. The M6-lip1- mutant was detected in a mutant library screen aimed at identifying M6 mutants with altered levels of twitching motility. In this screen M6-lip1- was the only mutant that showed significantly larger twitching motility haloes around colonies than wild-type M6. Sequence analyses indicated that lip1 encodes a member of the GDSL family of secreted lipolytic enzymes. In line with this finding, lipolytic assays showed that the supernatants of M6-lip1- had lower lipolytic activity as compared with those of wild-type M6 and a lip1-complemented strain. The mutant was also affected in swimming motility and had compromised virulence on melon seedlings and on Nicotiana benthamiana leaves relative to wild-type and complemented strains. Lip1 contains a predicted N-terminal signal sequence for type II secretion. Evidence from our study confirms Lip1 is indeed secreted in a type II secretion-dependent manner, and this is required for full virulence of A. citrulli. To the best of our knowledge this is the first study reporting contribution of lipolytic activity to virulence of a plant-pathogenic Acidovorax species.

Dynamic Hybrid Flagellar Motors-Fuel Switch and More

Flagellar motors are intricate rotating nanomachines that are powered by transmembrane ion gradients. The stator complexes are the powerhouses of the flagellar motor: They convert a transmembrane ion gradient, mainly of H⁺ or Na⁺, into rotation of the helical flagellar filament. They are thus essential for motor function. The number of stators synchronously engaged in the motor is surprisingly dynamic and depends on the load and the environmental concentration of the corresponding coupling ion. Thus, the rotor-stator interactions determine an important part of the properties of the motor. Numerous bacteria have been identified as possessing more than one set of stators, and some species have been demonstrated to use these different stators in various configurations to modify motor functions by dynamic in-flight swapping. Here, we review knowledge of the properties, the functions, and the evolution of these hybrid motors and discuss questions that remain unsolved.

McvR, a single domain response regulator regulates motility and virulence in the plant pathogen Xanthomonas campestris

Signal transduction pathways mediated by sensor histidine kinases and cognate response regulators control a variety of physiological processes in response to environmental conditions in most bacteria. Comparatively little is known about the mechanism(s) by which single-domain response regulators (SD-RRs), which lack a dedicated output domain but harbour a phosphoryl receiver domain, exert their various regulatory effects in bacteria. Here we have examined the role of the SD-RR proteins encoded by the phytopathogen Xanthomonas campestris pv. campestris (Xcc). We describe the identification and characterization of a SD-RR protein named McvR (motility, chemotaxis, and virulence-related response regulator) that is required for virulence and motility regulation in Xcc. Deletion of the mcvR open reading frame caused reduced motility, chemotactic movement, and virulence in Xcc. Global transcriptome analyses revealed the McvR had a broad regulatory role and that most motility and pathogenicity genes were down-regulated in the mcvR mutant. Bacterial two-hybrid and protein pull-down assays revealed that McvR did not physically interact with components of the bacterial flagellum but interacts with other SD-RR proteins (like CheY) and the subset of DNA-binding proteins involved in gene regulation. Site-directed mutagenesis and phosphor-transfer experiments revealed that the aspartyl residue at position 55 of the receiver domain is important for phosphorylation and the regulatory activity of McvR protein. Taken together, the findings describe a previously unrecognized class of SD-RR protein that contributes to the regulation of motility and virulence in Xcc.

Enhancing Metabolic Efficiency through Optimizing Metabolizable Protein Profile in a Time Progressive Manner with Weaned Goats as a Model: Involvement of Gut Microbiota

Feeding a growing global population and lowering environmental pollution are the two biggest challenges facing ruminant livestock. Considering the significance of nitrogen metabolism in these challenges, a dietary intervention regarding metabolizable protein profiles with different rumen-undegradable protein (RUP) ratios (high RUP [HRUP] versus low RUP [LRUP]) was conducted in young ruminants with weaned goats as a model. Fecal samples were collected longitudinally for nine consecutive weeks to dissect the timing and duration of intervention, as well as its mechanism of action involving the gut microbiota. Results showed that at least 6 weeks of intervention were needed to distinguish the beneficial effects of HRUP, and HRUP intervention improved the metabolic efficiency of goats as evidenced by enhanced growth performance and nutrient-apparent digestibility at week 6 and week 8 after weaning. Integrated analysis of bacterial diversity, metabolites, and inferred function indicated that HRUP intervention promoted Eubacterium abundance, several pathways related to bacterial chemotaxis pathway, ABC transporters, and butanoate metabolism and thereafter elicited a shift from acetate production toward butyrate and branched-chain amino acid (BCAA) production. Meanwhile, three distinct phases of microbial progression were noted irrespective of dietary treatments, including the enrichment of fiber-degrading Ruminococcus, the enhancement of microbial cell motility, and the shift of fermentation type as weaned goats aged. The current report provides novel insights into early-life diet-microbiota axis triggered by metabolic protein intervention and puts high emphasis on the time window and duration of dietary intervention in modulating lifelong performance of ruminants. IMPORTANCE Precise dietary intervention in early-life gastrointestinal microbiota has significant implications in the long-life productivity and health of young ruminants, as well as in lowering their environmental footprint. Here, using weaned goats as a model, we report that animals adapted to high rumen-undegradable protein diet in a dynamic manner by enriching fecal community that could effectively move toward and scavenge nutrients such as glucose and amino acids and, thereafter, elicit butyrate and BCAA production. Meanwhile, the three dynamic assembly trajectories in fecal microbiota highlight the importance of taking microbiota dynamics into account. Our findings systematically reported when, which, and how the fecal microbiome responded to metabolizable protein profile intervention in young ruminants and laid a foundation for improving the productivity and health of livestock due to the host-microbiota interplay.