AFM resolves effects of ethambutol on nanomechanics and nanostructures of single dividing mycobacteria in real-time

A hermetically closed sample chamber enables time-lapse nano-characterization of pathogenic microorganisms in vitro

Pathogenic microorganisms, such as pathogenic mycobacteria, pose a global health burden. Studying these organisms is crucial for gaining detailed knowledge about the pathogens and the diseases they cause. To handle pathogenic organisms, specific biosafety measures appropriate to the virulence of the organism must be fulfilled, most importantly ensuring that all manipulations of pathogenic material are performed within a confined environment. Atomic force microscopy (AFM) is a powerful technique to study biological samples at nanometer-scale resolution, yielding also mechanical properties, all while maintaining physiological conditions. However, standard AFM sample holders do not meet stringent biosafety requirements since they do not constitute a confined system. AFM imaging relies on direct contact between the cantilever and the sample and is sensitive to mechanical interference, rendering conventional containment systems for handling infectious substances inapplicable. Here, we introduce a hermetically sealed AFM sample chamber that meets biosafety demands while satisfying the mechanical and optical constraints of correlated optical microscopy and AFM. We imaged various pathogenic mycobacteria to demonstrate the chamber's versatility and effectiveness in containing biohazardous materials. This sample chamber enables high-resolution, time-lapse correlated imaging and biomechanical characterization of pathogenic microorganisms in vitro. It broadens the scope of research with pathogenic microorganisms under safe and controlled conditions.

Atomic force microscopy and surface plasmon resonance for real-time single-cell monitoring of bacteriophage-mediated lysis of bacteria

The growing incidence of multidrug-resistant bacterial strains presents a major challenge in modern medicine. Antibiotic resistance is often exhibited by Staphylococcus aureus, which causes severe infections in human and animal hosts and leads to significant economic losses. Antimicrobial agents with enzymatic activity (enzybiotics) and phage therapy represent promising and effective alternatives to classic antibiotics. However, new tools are needed to study phage-bacteria interactions and bacterial lysis with high resolution and in real-time. Here, we introduce a method for studying the lysis of S. aureus at the single-cell level in real-time using atomic force microscopy (AFM) in liquid. We demonstrate the ability of the method to monitor the effect of the enzyme lysostaphin on S. aureus and the lytic action of the Podoviridae phage P68. AFM allowed the topographic and biomechanical properties of individual bacterial cells to be monitored at high resolution over the course of their lysis, under near-physiological conditions. Changes in the stiffness of S. aureus cells during lysis were studied by analyzing force-distance curves to determine Young's modulus. This allowed observing a progressive decline in cellular stiffness corresponding to the disintegration of the cell envelope. The AFM experiments were complemented by surface plasmon resonance (SPR) experiments that provided information on the kinetics of phage-bacterium binding and the subsequent lytic processes. This approach forms the foundation of an innovative framework for studying the lysis of individual bacteria that may facilitate the further development of phage therapy.

Seeing and Touching the Mycomembrane at the Nanoscale

Mycobacteria have unique cell envelopes, surface properties, and growth dynamics, which all play a part in the ability of these important pathogens to infect, evade host immunity, disseminate, and resist antibiotic challenges. Recent atomic force microscopy (AFM) studies have brought new insights into the nanometer-scale ultrastructural, adhesive, and mechanical properties of mycobacteria. The molecular forces with which mycobacterial adhesins bind to host factors, like heparin and fibronectin, and the hydrophobic properties of the mycomembrane have been unraveled by AFM force spectroscopy studies. Real-time correlative AFM and fluorescence imaging have delineated a complex interplay between surface ultrastructure, tensile stresses within the cell envelope, and cellular processes leading to division. The unique capabilities of AFM, which include subdiffraction-limit topographic imaging and piconewton force sensitivity, have great potential to resolve important questions that remain unanswered on the molecular interactions, surface properties, and growth dynamics of this important class of pathogens.

Vγ9Vδ2 T cells strengthen cisplatin inhibition activity against breast cancer MDA-MB-231 cells by disrupting mitochondrial function and cell ultrastructure

BACKGROUND

Breast cancer ranks second of new cases and fifth of death in 2018 worldwide. Cis-platinum (CDDP) has been used as a chemotherapy to treat breast cancer for years. However, CDDP can adversely disrupt immune function of host. Thus, development of new protocol that can minimize side effect and meanwhile elevate clinical efficacy of CDDP will eventually benefit cancer patients. Since Vγ9Vδ2 T cells can up-regulate immune function of cancer patients, therefore, our hypothesis is that introduction of Vγ9Vδ2 T cells could potentiate CDDP efficacy against breast cancer.

METHODS

We used breast cancer cell line MDA-MB-231 as model cell to test our hypothesis. The cancer cell viability in vitro in the context of different dose of CDDP was analyzed by flow cytometry. The cytoskeleton alteration was visualized by confocal microscopy, and the ultrastructure of cell membrane was observed by atomic force microscopy. The mitochondrial function of MDA-MB-231 cells was detected as well by flow cytometry.

RESULTS

Comparing to either Vγ9Vδ2 T cells or CDDP alone, Vγ9Vδ2 T cells plus CDDP could more strikingly induce MDA-MB-231 cell membrane ultrastructure disruption and cytoskeleton disorder, and more significantly enhance the inhibition of CDDP on proliferation of MDA-MB-231 cells. At the same time, Vγ9Vδ2 T cells strengthened CDDP-induced mitochondrial dysfunction of cancer cells.

CONCLUSION

This work revealed that Vγ9Vδ2 T cells could synergistically enhance the inhibition activity of CDDP against breast cancer cells. Meanwhile, this in vitro proof-of-concept study implied the clinical prospect of the combining application of Vγ9Vδ2 T cells and CDDP in breast cancer therapy.

Scratching the Surface: Bacterial Cell Envelopes at the Nanoscale

The bacterial cell envelope is essential for viability, the environmental gatekeeper and first line of defense against external stresses. For most bacteria, the envelope biosynthesis is also the site of action of some of the most important groups of antibiotics. It is a complex, often multicomponent structure, able to withstand the internally generated turgor pressure. Thus, elucidating the architecture and dynamics of the cell envelope is important, to unravel not only the complexities of cell morphology and maintenance of integrity but also how interventions such as antibiotics lead to death. To address these questions requires the capacity to visualize the cell envelope in situ via high-spatial resolution approaches. In recent years, atomic force microscopy (AFM) has brought novel molecular insights into the assembly, dynamics, and functions of bacterial cell envelopes. The ultrafine resolution and physical sensitivity of the technique have revealed a wealth of ultrastructural features that are invisible to traditional optical microscopy techniques or imperceptible in their true physiological state by electron microscopy. Here, we discuss recent progress in our use of AFM imaging for understanding the architecture and dynamics of the bacterial envelope. We survey recent studies that demonstrate the power of the technique to observe isolated membranes and live cells at (sub)nanometer resolution and under physiological conditions and to track in vitro structural dynamics in response to growth or to drugs.

Chitosan Nanoparticles Strengthen Vγ9Vδ2 T-Cell Cytotoxicity Through Upregulation Of Killing Molecules And Cytoskeleton Polarization

Background

During the past few years, immune cell therapy for malignant cancer has benefited a considerable amount of patients worldwide. As one of several promising candidates for immunotherapy, Vγ9Vδ2 γδ T cells have many unique biological advantages, such as non-MHC restriction and have been noted as the earliest source of IFN-γ. However, potentiating anti-tumor functions of γδ T cells has become of particular interest to researchers studying γδ T cell applications.

Purpose

In this study, we proposed a nanotechnology-based methodology for strengthening γδ T cell functions.

Methods

As a type of reliable, biocompatible material, chitosan nanoparticles (CSNPs) were used to enhance anti-tumor immunity of γδ T cells.

Results

First, we found that the size of prepared CSNPs distributed 50 to 100 nm, and that CSNPs had optimal immunocompatibility. Then, we observed that CSNPs could induce α-tubulin cytoskeleton polarization and rearrangement, correlating with a higher killing ability of γδ T cells. Furthermore, we revealed that CSNPs could enhance Vγ9Vδ2 T cell anti-tumor functions by upregulating killing of related receptors, including NKG2D, CD56, FasL, and perforin secretion.

Conclusion

Our work provided evidence of application for CSNPs based bio-carrier in immunotherapy. More importantly, we proposed a new strategy for enhancing γδ T cell anti-tumor activity using nanobiomaterial, which could benefit future clinical applications of γδ T cells.

Selenium nanoparticles as new strategy to potentiate γδ T cell anti-tumor cytotoxicity through upregulation of tubulin-α acetylation

Immune cell therapy presents a paradigm for the treatment of malignant tumors. Human Vγ9Vδ2 T cells, a subset of peripheral γδ T cells, have been shown to have promising anti-tumor activity. However, new methodology on how to achieve a stronger anti-tumor activity of Vγ9Vδ2 T cells is under continuous investigation. In this work, we used selenium nanoparticles (SeNPs) to strengthen the anti-tumor cytotoxicity of Vγ9Vδ2 T cells. We found SeNPs pretreated γδ T cells had significantly stronger cancer killing and tumor growth inhibition efficacy when compared with γδ T cells alone. Simultaneously, SeNPs pretreatment could significantly upregulate the expression of cytotoxicity related molecules including NKG2D, CD16, and IFN-γ, meanwhile, downregulate PD-1 expression of γδ T cells. Importantly, we observed that SeNPs promoted tubulin acetylation modification in γδ T cells through interaction between microtubule network and lysosomes since the latter is the primary resident station of SeNPs shown by confocal visualization. In conclusion, SeNPs could significantly potentiate anti-tumor cytotoxicity of Vγ9Vδ2 T cells, and both cytotoxicity related molecules and tubulin acetylation were involved in fine-tuning γδ T cell toxicity against cancer cells. Our present work demonstrated a new strategy for further enhancing anti-tumor cytotoxicity of human Vγ9Vδ2 T cells by using SeNPs-based nanotechnology, not gene modification, implicating SeNPs-based nanotechnology had a promising clinical perspective in the γδ T cell immunotherapy for malignant tumors.

Division site selection linked to inherited cell surface wave troughs in mycobacteria

Cell division is tightly controlled in space and time to maintain cell size and ploidy within narrow bounds. In bacteria, the canonical Minicell (Min) and nucleoid occlusion (Noc) systems together ensure that division is restricted to midcell after completion of chromosome segregation¹. It is unknown how division site selection is controlled in bacteria that lack homologues of the Min and Noc proteins, including mycobacteria responsible for tuberculosis and other chronic infections². Here, we use correlated optical and atomic-force microscopy^3,4 to demonstrate that morphological landmarks (waveform troughs) on the undulating surface of mycobacterial cells correspond to future sites of cell division. Newborn cells inherit wave troughs from the (grand)mother cell and ultimately divide at the centre-most wave trough, making these morphological features the earliest known landmark of future division sites. In cells lacking the chromosome partitioning (Par) system, missegregation of chromosomes is accompanied by asymmetric cell division at off-centre wave troughs, resulting in the formation of anucleate cells. These results demonstrate that inherited morphological landmarks and chromosome positioning together restrict mycobacterial division to the midcell position.

Computer vision distortion correction of scanning probe microscopy images

Since its inception, scanning probe microscopy (SPM) has established itself as the tool of choice for probing surfaces and functionalities at the nanoscale. Although recent developments in the instrumentation have greatly improved the metrological aspects of SPM, it is still plagued by the drifts and nonlinearities of the piezoelectric actuators underlying the precise nanoscale motion. In this work, we present an innovative computer-vision-based distortion correction algorithm for offline processing of functional SPM measurements, allowing two images to be directly overlaid with minimal error – thus correlating position with time evolution and local functionality. To demonstrate its versatility, the algorithm is applied to two very different systems. First, we show the tracking of polarisation switching in an epitaxial Pb(Zr_0.2Ti_0.8)O₃ thin film during high-speed continuous scanning under applied tip bias. Thanks to the precise time-location-polarisation correlation we can extract the regions of domain nucleation and track the motion of domain walls until the merging of the latter in avalanche-like events. Secondly, the morphology of surface folds and wrinkles in graphene deposited on a PET substrate is probed as a function of applied strain, allowing the relaxation of individual wrinkles to be tracked.

Real-Time Observation of Antimicrobial Polycation Effects on Escherichia coli: Adapting the Carpet Model for Membrane Disruption to Quaternary Copolyoxetanes

Real-time atomic force microscopy (AFM) was used for analyzing effects of the antimicrobial polycation copolyoxetane P[(C12)-(ME2Ox)-50/50], C12-50 on the membrane of a model bacterium, Escherichia coli (ATCC# 35218). AFM imaging showed cell membrane changes with increasing C12-50 concentration and time including nanopore formation and bulges associated with outer bacterial membrane disruption. A macroscale bactericidal concentration study for C12-50 showed a 4 log kill at 15 μg/mL with conditions paralleling imaging (1 h, 1x PBS, physiological pH, 25 °C). The dramatic changes from the control image to 1 h after introducing 15 μg/mL C12-50 are therefore reasonably attributed to cell death. At the highest concentration (60 μg/mL) further cell membrane disruption results in leakage of cytoplasm driven by detergent-like action. The sequence of processes for initial membrane disruption by the synthetic polycation C12-50 follows the carpet model posited for antimicrobial peptides (AMPs). However, the nanoscale details are distinctly different as C12-50 is a synthetic, water-soluble copolycation that is best modeled as a random coil. In a complementary AFM study, chemical force microscopy shows that incubating cells with C12-50 decreased the hydrophobicity across the entire cell surface at an early stage. This finding provides additional evidence indicating that C12-50 polycations initially bind with the cell membrane in a carpet-like fashion. Taken together, real time AFM imaging elucidates the mechanism of antimicrobial action for copolyoxetane C12-50 at the single cell level. In future work this approach will provide important insights into structure-property relationships and improved antimicrobial effectiveness for synthetic amphiphilic polycations.