Motility Of Microorganisms Research Articles

Peristaltic transport of viscoelastic fluid in curved ducts with ciliated walls

The transport of complex rheological fluids in physiological ducts is often facilitated by the dynamic phenomenon of peristalsis. Additionally, peristaltic transport assisted by cilia plays a significant role in various natural processes such as respiration, circulation, locomotion, and reproduction. This study focuses on magnetically induced flow bounded by non-uniform curved walls, motivated by the importance of peristalsis and micro-organism motility. To characterize the complex rheology of the fluid liner, a viscoelastic model described by the constitutive equation of Jeffrey's fluid is employed. The flow problem is mathematically formulated using curvilinear coordinates. Subsequently, linear transformations and scaling factors are applied to convert the equations into dimensionless form, while considering biotic restrictions such as creeping transport and long wavelength to reduce dependent variables. By utilizing the stream function and cross-differentiation, a fourth-order equation is obtained and numerically approximated using the shooting method. The effects of various parameters on the flow are illustrated through graphs, and a physical interpretation of the graphical results is provided. It is observed that ciliated walls of the channel enhance the velocity and pumping, while trapping phenomena are more pronounced in a non-uniform channel compared to a uniform channel.

Unraveling the mechanisms behind sodium persulphate-induced changes in petroleum-contaminated aquifers’ biogeochemical parameters and microbial communities

Sodium persulphate (PS) is a highly effective oxidising agent widely used in groundwater remediation and wastewater treatment. Although numerous studies have examined the impact of PS with respect to the removal efficiency of organic pollutants, the residual effects of PS exposure on the biogeochemical parameters and microbial ecosystems of contaminated aquifers are not well understood. This study investigates the effects of exposure to different concentrations of PS on the biogeochemical parameters of petroleum-contaminated aquifers using microcosm batch experiments. The results demonstrate that PS exposure increases the oxidation-reduction potential (ORP) and electrical conductivity (EC), while decreasing total organic carbon (TOC), dehydrogenase (DE), and polyphenol oxidase (PO) in the aquifer. Three-dimensional excitation-emission matrix (3D-EEM) analysis indicates PS is effective at reducing fulvic acid-like and humic acid-like substances and promoting microbial metabolic activity. In addition, PS exposure reduces the abundance of bacterial community species and the diversity index of evolutionary distance, with a more pronounced effect at high PS concentrations (31.25 mmol/L). Long-term (90 d) PS exposure results in an increase in the abundance of microorganisms with environmental resistance, organic matter degradation, and the ability to promote functional genes related to biological processes such as basal metabolism, transmission of genetic information, and cell motility of microorganisms. Structural equation modeling (SEM) further confirms that ORP and TOC are important drivers of change in the abundance of dominant phyla and functional genes. These results suggest exposure to different concentrations of PS has both direct and indirect effects on the dominant phyla and functional genes by influencing the geochemical parameters and enzymatic activity of the aquifer. This study provides a valuable reference for the application of PS in ecological engineering.

Magneto-Rotational Augmentation of Bioconvective Transport in Plasma-Nanofluid Flowing through a Penetrable Spinning Disc

The phenomenon of bioconvective transport through the manipulation of motile microorganisms is considered a promising process control technique in several biological processes and microdevices. Inducing convective transport in self-propelling microbes could be tailored to improve mixing, reaction propensity, and concentration transport within the media. This paper examined the combined effect of magnetic and rotational fields on the argumentation of bioconvective transport in the nanofluid-mediated plasma flow. A detailed analysis of the transport and dynamics of reactive forces during bioconvection in a rotary disc-like microchannel is presented. The physics of the problem was described by coupled nonlinear ordinary differential equations, which were numerically computed using the spectral relaxation scheme of the spectral homotopy analysis method. It was observed that the imposition of a magnetic field constituted viscous drag in the plasma-nanofluid media, which consequently increases the thermophoretic parameter in the bioconvective flow. It was ascertained that coupled magnetic and rotational effects significantly augmented the motility of microorganisms and translated to growth in momentum and concentration fields which is noticeable in the generation of stretching effect on the bacterium-containing plasma-nanofluid flow. The findings of this study could provide an essential basis for the design of bioreactors, centrifugal microfluidics technologies, and microdevices for use in a broad spectrum of biotechnology.

Effects of Ethyl Lauroyl Arginate (LAE) on Biofilm Detachment: Shear Rate, Concentration, and Dosing Time

Biofilm formation is one of the main obstacles in membrane treatment. The non-oxidizing biocide ethyl lauroyl arginate (LAE) is promising for mitigating biofilm development on membrane surfaces. However, the operating conditions of LAE and their impact on biofilm detachment are not comprehensively understood. In this study, a real-time in vitro flow cell system was utilized to observe biofilm dispersal caused by the shear rate, concentration, and treatment time of LAE. This confirmed that the biofilm was significantly reduced to 68.2% at a shear rate of 3.42 s−1 due to the increased physical lifting force. LAE exhibited two different mechanisms for bacterial inactivation and biofilm dispersal. Biofilms treated with LAE at sub-growth inhibitory concentrations for a longer time could effectively detach the biofilm formed on the surface of the glass slides, which can be attributed to the increased motility of microorganisms. However, a high concentration (i.e., bactericidal concentration) of LAE should be seriously considered because of the inactivated sessile bacteria and their residual debris remaining on the surface. This study sheds light on the effect of LAE on biofilm detachment and provides insights into biofouling mitigation during the membrane process.

Digital holography-based 3D particle localization for single-molecule tweezer techniques

We present a three-dimensional (3D) imaging technique for the fast tracking of microscopic objects in a fluid environment. Our technique couples digital holographic microscopy with three-dimensional localization via parabolic masking. Compared with existing approaches, our method reconstructs 3D volumes from single-plane images, which greatly simplifies image acquisition, reduces the demand on microscope hardware, and facilitates tracking higher densities of microscopic particles while maintaining similar levels of precision. We demonstrate utility of this method in magnetic tweezer experiments, opening their use to multiplexed single-molecule force spectroscopy assays, which were previously limited by particle crowding and fast dissociation times. We propose that our technique will also be useful in other applications that involve the tracking of microscopic objects in three dimensions, such as studies of microorganism motility and 3D flow characterization of microfluidic devices.

Nano zero-valent iron improves anammox activity by promoting the activity of quorum sensing system

The addition of nano zero-valent iron (nZVI) has been proven to improve the efficiency of the anammox process, however, the mechnism is not clear. Here, the effect of nZVI on anammox microbial community was studied by metagenomic sequencing methods. It was found that 50 mg/L nZVI indeed promoted the removal of NH4+ and NO2− of the anammox reactor and significantly improved the relative abundance of AnAOB (Ca. Brocadia) from 42.1% to 52.5%. What's more, 50 mg/L nZVI increased the abundance of c-di-GMP synthesized protein from 148 rpmr to 252 rpmr in the microbial community and decreased the abundance of c-di-GMP degradation protein from 238 rpmr to 204 rpmr, which indirectly led to the enrichment of c-di-GMP in the microbial community. The enrichment of c-di-GMP reduced the motility of microorganisms in the reactor and promoted the secretion of extracellular polymers by bacteria, which is beneficial to the formation of sludge particles in the anammox reactor. In conclusion, this research clarified the mechanism of nZVI promoting the anammox process and provided theoretical guidance for the engineering application of anammox.

Dynamic guiding of bacteria in lyotropic chromonic liquid crystal using magnetic field

This article demonstrates a new approach enabling the active control of swimming trajectories of flagellated bacteria in space and time. Bacteria were mixed with water solutions of disodium cromoglycate (DSCG), a lyotropic chromonic liquid crystal (LCLC) that mimics the anisotropic properties of many biological environments. It has been well established that the bacteria then swim in the direction of the self-aligned molecular aggregates of DSCG. It is also known that this host material possesses a diamagnetic anisotropy enabling the control of the local orientation of these aggregates with magnetic fields (MF). This double coupling (bacteria-LCLC & LCLC-MF) allows the efficient real-time control of the orientation of bacterial trajectories. Such control over the motility of microorganisms opens numerous avenues for their manipulation and study, for example, in a lab-on-a-chip device.

Hydrodynamic Interaction Enhances Colonization of Sinking Nutrient Sources by Motile Microorganisms.

In this study, we document hydrodynamics-mediated trapping of microorganisms around a moving spherical nutrient source such as a settling marine snow aggregate. There exists a range of size and excess density of the nutrient source, and motility and morphology of the microorganism under which hydrodynamic interactions enable the passive capture of approaching microorganisms onto a moving nutrient source. We simulate trajectories of chemotactic and non-chemotactic bacteria encountering a sinking marine snow particle effusing soluble nutrients. We calculate the average nutrient concentration to which the bacteria are exposed, under regimes of strong and weak hydrodynamic trapping. We find that hydrodynamic trapping can significantly amplify (by ≈40%) the nutrient exposure of bacteria, both chemotactic and non-chemotactic. The subtle interactions between hydrodynamic and chemotactic effects reveal non-trivial variations in this “hydrodynamic amplification,” as a function of relevant biophysical parameters. Our study provides a consistent description of how microorganism motility, fluid flow and nutrient distribution affect foraging by marine microbes, and the formation of biofilms on spherical nutrient sources under the influence of fluid flow.

Enhanced diffusometric immunosensing with grafted gold nanoparticles for detection of diabetic retinopathy biomarker tumor necrosis factor-α

Diffusometry is sensitive to geometric changes of particles. Target antigens can be detected through diffusivity changes resulting from their immunoreactions by functionalizing particle surface with a specific antibody. Considering that Brownian motion is a self-driven phenomenon, diffusometric immunosensing features several characteristics, such as no-washing steps, rapid detection, high flexibility, and high sensitivity. Until recently, this technique has been applied to many biomedical fields, such as monitoring of microorganism motility and diagnosis of diseases with biomarkers. Despite the abovementioned advantages, diffusivity changes in conventional diffusometry can be compromised at low-abundance antigens because proteins are much smaller than capture particles. To overcome such restriction, we present an improved diffusometric immunosensing technique by grafting additional gold nanoparticles (AuNPs) to capture particles to enhance size changes. A diabetic retinopathy (DR) biomarker, tumor necrosis factor-α was selected to evaluate the proposed immunosensing technique. Spherical AuNPs showed better enhancement than rod-like AuNPs during measurement. Limit of detection was improved by at least 100-fold down to 10pg/mL. A dichotomous method was also developed to enable rapid detection and avoid tedious calibration. The relationship of concentrations between the two solutions used can be explicitly determined by comparing diffusivity of an unknown concentration of target molecules with that of a reference solution. Minimum discernible concentration reached as low as twofold higher or lower than basal concentration. Tear samples were collected from four volunteers, including three healthy subjects and one proliferative DR patient to prove the concept in diagnosis of the disease. All data showed good agreement with preset conditions. The technique eventually provides an insight into rapid diagnoses of diseases in the early stage.

Relationship Between Oral Microorganisms and Dental Caries

Objectives: The purpose of this study was to investigate the relationship between the incidences of dental caries and the amount and motility of oral microorganisms in inter proximal dental plaque. Methods: Oral microorganism samples from 240 volunteers in six different age groups were classified according to morphology using phase contrast microscopy. We observed the amount and motility of the microorganisms and examined for relationships to the incidences of dental caries. Results: There was a statistically significant difference among the age groups (p < 0.05) in the motility of cocci and bacilli and in the amount of spirilla. The decayed tooth (DT), filled tooth (FT), and decayed, missing, filled tooth (DMFT) index for all age groups were calculated as 7.5 ± 4.5, 1.9 ± 3.0, and 14.8 ± 8.1. There was weak, positive relationship between the amount of cocci and bacilli and caries incidence, regardless of age (p < 0.01). Conclusion: Determining the amount and motility of oral microorganisms is an effective method of evaluating and controlling the status of oral health.

Hydrodynamic interactions of sheets vs filaments: Synchronization, attraction, and alignment

The synchronization of nearby sperm flagella as they swim in a viscous fluid was observed nearly a century ago. In the early 1950s, in an effort to shed light on this intriguing phenomenon, Taylor initiated the mathematical analysis of the fluid dynamics of microorganism motility. Since then, models have investigated sperm hydrodynamics where the flagellum is treated as a waving sheet (2D) or as a slender waving filament (3D). Here, we study the interactions of two finite length, flexible filaments confined to a plane in a 3D fluid and compare these to the interactions of the analogous pair of finite, flexible sheets in a 2D fluid. Within our computational framework using regularized Stokeslets, this comparison is easily achieved by choosing either the 2D or 3D regularized kernel to compute fluid velocities induced by the actuated structures. We find, as expected, that two flagella swimming with a symmetric beatform will synchronize (phase-lock) on a fast time scale and attract towards each other on a longer time scale in both 2D and 3D. For a symmetric beatform, synchronization occurs faster in 2D than 3D for sufficiently stiff swimmers. In 3D, a greater enhancement in efficiency and swimming velocity is observed for attracted swimmers relative to the 2D case. We also demonstrate the tendency of two asymmetrically beating filaments in a 3D fluid to align — in tandem — exhibiting an efficiency boost for the duration of their sustained alignment.

Computational fluid dynamics as a tool to understand the motility of microorganisms

In this work we demonstrate the utility of a new computational algorithm, based on the finite volume method, for simulating the motility of microorganisms. The approach is adopted from our work on discrete particle modeling. The shape of a swimming cell is reconstructed as a contiguous sequence of spherical particles at discrete locations on the surface of the cell head and flagella, and the motion of each sphere is prescribed from experimentally observed motions. The spherical particles contribute to the fluid’s momentum as point forces. By computing the hydrodynamic interaction of the prescribed motion, we can calculate a propulsive velocity. We extensively validate our model with analytical results and other established numerical methods. Both qualitative and quantitative agreement are demonstrated across a wide range of low Reynolds number phenomena. Since it is implemented as an add-on module to computational fluid dynamics solvers such as FLUENT or OpenFOAM, it has the potential for broad utility in the viscous regime.

Flagellar kinematics and swimming of algal cells in viscoelastic fluids.

The motility of microorganisms is influenced greatly by their hydrodynamic interactions with the fluidic environment they inhabit. We show by direct experimental observation of the bi-flagellated alga Chlamydomonas reinhardtii that fluid elasticity and viscosity strongly influence the beating pattern - the gait - and thereby control the propulsion speed. The beating frequency and the wave speed characterizing the cyclical bending are both enhanced by fluid elasticity. Despite these enhancements, the net swimming speed of the alga is hindered for fluids that are sufficiently elastic. The origin of this complex response lies in the interplay between the elasticity-induced changes in the spatial and temporal aspects of the flagellar cycle and the buildup and subsequent relaxation of elastic stresses during the power and recovery strokes.

Measuring the translational and rotational velocities of particles in helical motion using structured light.

We measure the rotational and translational velocity components of particles moving in helical motion under a Laguerre-Gaussian mode illumination. The moving particle reflects light that acquires an additional frequency shift proportional to the velocity of rotation in the transverse plane, on top of the usual frequency shift due to the longitudinal motion. We determined both the translational and rotational velocities of the particles by switching between two modes: by illuminating with a Gaussian beam, we can isolate the longitudinal frequency shift; and by using a Laguerre-Gaussian mode, the frequency shift due to the rotation can be determined. Our technique can be used to characterize the motility of microorganisms with a full three-dimensional movement.

Characterizations of kinetic power and propulsion of the nematode Caenorhabditis elegans based on a micro-particle image velocimetry system.

Quantifying the motility of micro-organisms is beneficial in understanding their biomechanical properties. This paper presents a simple image-based algorithm to derive the kinetic power and propulsive force of the nematode Caenorhabditis elegans. To avoid unnecessary disturbance, each worm was confined in an aqueous droplet of 0.5 μl. The droplet was sandwiched between two glass slides and sealed with mineral oil to prevent evaporation. For motion visualization, 3-μm fluorescent particles were dispersed in the droplet. Since the droplet formed an isolated environment, the fluid drag and energy loss due to wall frictions were associated with the worm's kinetic power and propulsion. A microparticle image velocimetry system was used to acquire consecutive particle images for fluid analysis. The short-time interval (Δt < 20 ms) between images enabled quasi real-time measurements. A numerical simulation of the flow in a straight channel showed that the relative error of this algorithm was significantly mitigated as the image was divided into small interrogation windows. The time-averaged power and propulsive force of a N2 adult worm over three swimming cycles were estimated to be 5.2 ± 3.1 pW and 1.0 ± 0.8 nN, respectively. In addition, a mutant, KG532 [kin-2(ce179) X], and a wild-type (N2) worm in a viscous medium were investigated. Both cases showed an increase in the kinetic power as compared with the N2 worm in the nematode growth medium due to the hyperactive nature of the kin-2 mutant and the high viscosity medium used. Overall, the technique deals with less sophisticated calculations and is automation possible.

Turbulent Fluid Acceleration Generates Clusters of Gyrotactic Microorganisms

The motility of microorganisms is often biased by gradients in physical and chemical properties of their environment, with myriad implications on their ecology. Here we show that fluid acceleration reorients gyrotactic plankton, triggering small-scale clustering. We experimentally demonstrate this phenomenon by studying the distribution of the phytoplankton Chlamydomonas augustae within a rotating tank and find it to be in good agreement with a new, generalized model of gyrotaxis. When this model is implemented in a direct numerical simulation of turbulent flow, we find that fluid acceleration generates multifractal plankton clustering, with faster and more stable cells producing stronger clustering. By producing accumulations in high-vorticity regions, this process is fundamentally different from clustering by gravitational acceleration, expanding the range of mechanisms by which turbulent flows can impact the spatial distribution of active suspensions.

Modeling the dynamics of an elastic rod with intrinsic curvature and twist using a regularized Stokes formulation

We develop a Lagrangian numerical algorithm for an elastic rod immersed in a viscous, incompressible fluid at zero Reynolds number. The elasticity of the rod is described by a version of the Kirchhoff rod model, where intrinsic curvature and twist are prescribed, and the fluid is governed by the Stokes equations in R3. The elastic rod is represented by a space curve corresponding to the centerline of the rod and an orthonormal triad, which encodes the bend and twist of the rod. In this method, the differences between the rod configuration and its intrinsic shape generate force and torque along the centerline. The coupling to the fluid is accomplished by the use of the method of regularized Stokeslets for the force and regularized rotlets for the torque. This technique smooths out the singularity in the fundamental solutions of the Stokes equations for the computation of the velocity of the rod centerline. In addition, the computation of the angular velocity of the rod requires the use of regularized (potential) dipoles. As a benchmark problem, we consider open and closed rods with intrinsic curvature and twist in a viscous fluid. Equilibrium configurations and dynamic instabilities are compared with known results in elastic rod theory. For cases when the exact solution is unknown, the numerical results are compared to those produced by the generalized immersed boundary (gIB) method, where the fluid is governed by the Navier–Stokes equations with small Reynolds number on a finite (periodic) domain. It is shown that the regularization method combined with Kirchhoff rod theory contributes substantially to the reduction of computation time and efficient memory usage in comparison to the gIB method. We also illustrate how the regularized method can be used to model microorganism motility where the organism is propelled by a flagellum propagating sinusoidal waves. The swimming speeds of this flagellum using the regularized Stokes formulation are matched well with classical asymptotic results of Taylor’s infinite cylinder in terms of frequency and amplitude of the undulation.

Differential Dynamic Microscopy: A High-Throughput Method for Characterizing the Motility of Microorganisms

We present a fast, high-throughput method for characterizing the motility of microorganisms in three dimensions based on standard imaging microscopy. Instead of tracking individual cells, we analyze the spatiotemporal fluctuations of the intensity in the sample from time-lapse images and obtain the intermediate scattering function of the system. We demonstrate our method on two different types of microorganisms: the bacterium Escherichia coli (both smooth swimming and wild type) and the biflagellate alga Chlamydomonas reinhardtii. We validate the methodology using computer simulations and particle tracking. From the intermediate scattering function, we are able to extract the swimming speed distribution, fraction of motile cells, and diffusivity for E. coli, and the swimming speed distribution, and amplitude and frequency of the oscillatory dynamics for C. reinhardtii. In both cases, the motility parameters were averaged over ∼104 cells and obtained in a few minutes.

Idling Time of Motile Bacteria Contributes to Retardation and Dispersion in Sand Porous Medium

The motility of microorganisms affects their transport in natural systems by altering their interactions with the solid phase of the soil matrix. To assess the effect of these interactions on transport parameters, a series of breakthrough curves (BTCs) for motile and nonmotile bacteria, including E. coli and P. putida species, were measured from a homogeneously packed sand column under three different interstitial velocities of 1 m/d, 5 m/d, and 10 m/d. BTCs for the nonmotile bacteria were nearly identical for all three flow rates, except that the recovery percentage at 1 m/d was reduced by 5% compared to the higher flow rates. In contrast, for the motile bacteria, the recovery percentages were not affected by flow rate, but their BTCs exhibited a higher degree of retardation and dispersion as the flow velocity decreased, which was consistent with increased idling times of the motile strains. The smooth-swimming mutant E. coli HCB437, which is unable to change its swimming direction after encountering the solid surfaces and thus has the largest idling time, also exhibited the greatest degree of retardation and dispersion. All of the experimental observations were compared to results from an advection-dispersion transport model with three fitting parameters: retardation factor (R), longitudinal dispersivity (α(L)), and attachment rate coefficient (k(att)). In addition, the single-collector efficiency (η₀) and collision efficiency (α) were calculated according to the colloid filtration theory (CFT), and confirmed that motile bacteria had lower collision efficiencies than nonmotile bacteria. This is consistent with previously reported observations that motile bacteria can avoid attachment to a solid surface by their active swimming capabilities. By quantifying the effect of bacterial motility on various transport parameters, more robust fate and transport models can be developed for decision-making related to environmental remediation strategies and risk assessment.

Disruption of Vertical Motility by Shear Triggers Formation of Thin Phytoplankton Layers

Thin layers of phytoplankton are important hotspots of ecological activity that are found in the coastal ocean, meters beneath the surface, and contain cell concentrations up to two orders of magnitude above ambient concentrations. Current interpretations of their formation favor abiotic processes, yet many phytoplankton species found in these layers are motile. We demonstrated that layers formed when the vertical migration of phytoplankton was disrupted by hydrodynamic shear. This mechanism, which we call gyrotactic trapping, can be responsible for the thin layers of phytoplankton commonly observed in the ocean. These results reveal that the coupling between active microorganism motility and ambient fluid motion can shape the macroscopic features of the marine ecological landscape.