Magnetotactic Bacteria Research Articles

Single-cell magnetotaxis in mucus-mimicking polymeric solutions.

Magnetotactic bacteria (MTB) are promising candidates for use as biomicrorobots in biomedical applications due to their motility, self-propulsion, and the ability to direct their navigation with an applied magnetic field. When in the body, the MTB may encounter non-Newtonian fluids such as blood plasma or mucus. However, their motility and the effectiveness of directed navigation in non-Newtonian fluids has yet to be studied on a single-cell level. In this work, we investigate motility of Magnetospirillum magneticum AMB-1 in three concentrations of polyacrylamide (PAM) solution, a mucus-mimicking fluid. The swimming speeds increase from 44.0 ± 13.6 μm/s in 0 mg/mL of PAM to 52.73 ± 15.6 μm/s in 1 mg/mL then decreases to 24.51 ± 11.7 μm/s in 2 mg/mL and 21.23 ± 10.5 μm/s in 3 mg/mL. This trend of a speed increase in low polymer concentrations followed by a decrease in speed as the concentration increases past a threshold concentration is consistent with other studies of motile, flagellated bacteria. Past this threshold concentration of PAM, there is a higher percentage of cells with an overall trajectory angle deviating from the angle of the magnetic field lines. There is also less linearity in the trajectories and an increase in reversals of swimming direction. Altogether, we show that MTB can be directed in polymer concentrations mimicking biological mucus, demonstrating the influence of the medium viscosity on the linearity of their trajectories which alters the effective path that could be predefined in Newtonian fluids when transport is achieved by magnetotaxis.

Stable pharmaceutical composition of cryo-protected non-pyrogenic isotonic chains of magnetosomes for efficient tumor cell destruction at 45 ± 1 °C under alternating magnetic field or ultrasound application.

We report a method to prepare biocompatible, stable, and highly pure iron oxide nano-minerals by following the steps consisting of: (i) amplifying magnetotactic bacteria in non-toxic minimal growth media; (ii) extracting magnetosomes from magnetotactic bacteria under alkaline lysis; (iii) heating magnetosomes above 400 °C to yield sterile magnetosome minerals, M-uncoated, devoid of active non-denatured bacterial organic material; (iv) coating M-uncoated with biocompatible carboxymethyl-dextran (CMD) compounds to yield stable M-CMD; (v) adding 5% sorbitol to M-CMD; and (vi) lyophilizing these mixtures, resulting in formulated nano-minerals in powder forms, designated as (M-CMD)F. The long-term stability of the final products is demonstrated by re-suspending (M-CMD)F in water after 12 months of storage, and by showing that these formulated magnetosomes have preserved their stability in suspension, chain arrangement, carbon content, surface charge, and surface composition. Furthermore, the formulation is optimized to yield an isotonic magnetosome suspension with an osmolality of between 275 and 290 mOsm kg-1 H2O upon reconstitution. On one hand, these formulated magnetosomes are fully biocompatible, i.e. sterile, non-pyrogenic, and non-cytotoxic towards 3T3, L929, and V79 healthy cells up to 1 mg mL-1 NP concentration iron. On the other hand, when they are brought into the presence of PC3-Luc prostate tumor cells and heated moderately at ∼41-46 °C for 20-30 minutes under low-intensity ultrasound or alternating magnetic field conditions, they efficiently destroy these tumor cells.

Influence of crystal shape and orientation on the magnetic microstructure of bullet-shaped magnetosomes synthesized by magnetotactic bacteria

Abstract Cells of magnetotactic bacteria are used as model systems for studying the magnetic properties of ferrimagnetic nanocrystals. Each individual bacterial strain produces magnetosomes (membrane-bounded magnetic crystals) that have distinct sizes, shapes, crystallographic orientations and spatial arrangements, thereby providing nanoparticle systems whose unique magnetic properties are unmatched by synthetic chemically-produced crystals. Here, we use off-axis electron holography in the transmission electron microscope to study the magnetic properties of isolated and closely-spaced bullet-shaped magnetite (Fe3O4) magnetosomes biomineralized by the following magnetotactic bacterial strains: the cultured Desulfovibrio magneticus RS-1 and the uncultured strains LO-1 and HSMV-1. These bacteria biomineralize magnetite crystals whose crystallographic axes of elongation are parallel to <100> (RS-1 and LO-1) or <110> (HSMV-1). We show that the individual magnetosome crystals are single magnetic domains and measure their projected in-plane magnetization distributions and magnetic dipole moments. We use analytical modelling to assess the interplay between shape anisotropy and the magnetically preferred <111> magneto-crystalline easy axis of magnetite.

Magnetic Resonance Imaging of Mammalian Cells Individually Expressing Membrane-Associated Magnetosome Proteins I, L, B, and E

The magnetosome, a membrane-bound iron biomineral formed within magnetotactic bacteria, is a unique model for a magnetic resonance imaging (MRI) reporter gene contrast agent. We are translating this technology to mammalian cells by expressing essential magnetosome genes mamI, mamL, mamB, and mamE into MDA-MB-435 human melanoma cells. Currently, these genes are individually expressed in the cell although the future goal is to express all four genes together. We examined the influence of these genes on cellular MRI relaxation rates by culturing cells in the presence and absence of iron-supplemented medium and scanning them at 3 Tesla using a gelatin phantom. Total cellular iron was measured by inductively-coupled plasma mass spectrometry and correlated with relaxation rates obtained from phantom experiments. Apart from mamE, magnetosome genes that are individually expressed in mammalian cells grown in iron supplement significantly affected cellular transverse relaxation rates compared to cells grown without iron supplement. Interestingly, mamI, mamL, mamB, and mamE (even though the latter had no effect on relaxation rate) significantly affected cellular iron content. This developing gene-based contrast agent will equip MRI with improvement to imaging sensitivity and the technology to track cellular activities long term.

Engineering Living Immunotherapeutic Agents for Improved Cancer Treatment

AbstractBacteria‐based agents are emerging as promising tools for cancer therapy due to their ability to actively target tumors, trigger localized inflammation, and induce tumor regression. There has been growing interest in using bacteria that are responsive to external cues, such as magnetic fields, to facilitate the formation of robust colonies in tumors and achieve the threshold for clinical efficacy. Several studies have demonstrated the potential of innately magnetically responsive bacteria, known as magnetotactic bacteria (MTB), as steerable agents. However, their immunostimulatory properties, which play a central role in their function as therapeutic agents, have not yet been adequately studied. Here, key aspects of human immune cell response to MTB strain Magnetospirillum magneticum AMB‐1 in physiological environments are characterized. The ability of MTB to maintain magnetic properties, remain viable in whole blood, elicit cytokine production by macrophages, and stimulate uptake of cancer cell material by dendritic cells is examined. This study also investigates the use of MTB–liposome complexes for effective delivery of therapeutic payloads in vitro and explores response to the agent in vivo. Overall, this work establishes the potential of MTB as a versatile, combined delivery platform for immune‐mediated cancer therapy.

Electroactivity of the magnetotactic bacteria Magnetospirillum magneticum AMB-1 and Magnetospirillum gryphiswaldense MSR-1

Magnetotactic bacteria reside in sediments and stratified water columns. They are named after their ability to synthesize internal magnetic particles that allow them to align and swim along the Earth’s magnetic field lines. Here, we show that two magnetotactic species, Magnetospirillum magneticum strain AMB-1 and Magnetospirillum gryphiswaldense strain MSR-1, are electroactive. Both M. magneticum and M. gryphiswaldense were able to generate current in microbial fuel cells with maximum power densities of 27 and 11 µW/m2, respectively. In the presence of the electron shuttle resazurin both species were able to reduce the crystalline iron oxide hematite (Fe2O3). In addition, M. magneticum could reduce poorly crystalline iron oxide (FeOOH). Our study adds M. magneticum and M. gryphiswaldense to the growing list of known electroactive bacteria, and implies that electroactivity might be common for bacteria within the Magnetospirillum genus.

Effects of static magnetic field on the sulfate metabolic pathway involved in Magnetospirillum magneticum AMB-1 cell growth and magnetosome formation.

Magnetotactic bacteria (MTB) can use their unique intracellular magnetosome organelles to swim along the Earth's magnetic field. They play important roles in the biogeochemical cycles of iron and sulfur. Previous studies have shown that the applied magnetic fields could affect the magnetosome formation and antioxidant defense systems in MTB. However, the molecular mechanisms by which magnetic fields affect MTB cells remain unclear. We aim to better understand the dark at 28°C-29°C for 20 h, as shownthe interactions between magnetic fields and cells, and the mechanism of MTB adaptation to magnetic field at molecular levels. We performed microbiological, transcriptomic, and genetic experiments to analyze the effects of a weak static magnetic field (SMF) exposure on the cell growth and magnetosome formation in the MTB strain Magnetospirillum magneticum AMB-1. The results showed that a 1.5 mT SMF significantly promoted the cell growth but reduced magnetosome formation in AMB-1, compared to the geomagnetic field. Transcriptomic analysis revealed decreased expression of genes primarily involved in the sulfate reduction pathway. Consistently, knockout mutant lacking adenylyl-sulfate kinase CysC did no more react to the SMF and the differences in growth and Cmag disappeared. Together with experimental findings of increased reactive oxidative species in the SMF-treated wild-type strain, we proposed that cysC, as a key gene, can participate in the cell growth and mineralization in AMB-1 by SMF regulation. This study suggests that the magnetic field exposure can trigger a bacterial oxidative stress response involved in AMB-1 growth and magnetosome mineralization by regulating the sulfur metabolism pathway. CysC may serve as a pivotal enzyme in mediating sulfur metabolism to synchronize the impact of SMF on both growth and magnetization of AMB-1.

Abstract LB_B23: Magnetospirillum magneticum promotes iron competition and triggers apoptosis in human cancer cells

Abstract Bacteria are increasingly envisioned as living agents that can be administered to patients to carry out therapeutic actions. Interest has been growing over the past years in harnessing these microorganisms for cancer treatment as dynamic vectors with enhanced tumor-targeting properties. While bacterial traits, such as modulation of an immune response, local secretion of toxins, and proliferation in tumors have been well studied, less is known about bacteria as competitors for nutrients. We, therefore, investigated the use of magnetotactic bacteria as living iron chelators in the tumor microenvironment by studying the resulting competition for this vital nutrient, and by investigating the consequent metabolic effects in cancer cells. To do this, we first recreated a hypoxic environment by establishing an in vitro co-culture system consisting of the magnetotactic strain Magnetospirillum magneticum AMB-1 incubated under low-oxygen conditions with human cancer cells. We first quantified bacterial siderophore production and found it to be equivalent to a relevant concentration of deferoxamine (DFO), a potent drug used in iron chelation therapy. Further experiments then revealed an increased expression of transferrin receptor 1 (TfR1) on the cell surface and a significant decrease of viability in various cancer cell lines, indicating the bacteria’s ability to alter iron homeostasis. Metabolic effects exerted by AMB-1 were then further investigated. We demonstrated a lower rate of cellular proliferation correlating with a growing ratio of bacteria to cancer cells. Additional experiments also confirmed elevated apoptotic states and an enhanced activity level of executioner caspases in cancer cells, with an increasing number of AMB-1 in the culture. Lastly, the performed assays uncovered several apoptosis-related proteins that displayed altered levels when AMB-1 bacteria were added to the culture. Overall, our findings show the potential of magnetotactic bacteria to act as self-replicating iron-chelating agents that interfere with the iron homeostasis of cancer cells and decrease cancer cell viability. The presented data suggests involvement of triggered apoptotic signals that correlate with an increasing number of AMB-1 in the culture. This intrinsic capability of AMB-1 to induce apoptosis in breast cancer cells thus represents an encouraging strategy that could serve as an additional antineoplastic approach to reinforce current bacterial cancer therapies. Citation Format: Stefano Menghini, Matej Vizovišek, Ping Shu Ho, Jonathas Enders, Simone Schürle. Magnetospirillum magneticum promotes iron competition and triggers apoptosis in human cancer cells [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr LB_B23.

Phylogenetics and biomineralization of a novel magnetotactic Gammaproteobacterium from a freshwater lake in Beijing, China.

Magnetotactic bacteria (MTB) have the remarkable capability of producing intracellularly membrane-enveloped magnetic nanocrystals (i.e. magnetosomes) and swimming along geomagnetic field lines. Despite more than 50 years of research, bacterial diversity and magnetosome biomineralization within MTB are relatively less known in the Gammaproteobacteria class than other groups. This is incompatible with the status of Gammaproteobacteria as the most diverse class of gram-negative bacteria with a number of ecologically important bacteria. Here, we identify a novel MTB strain YYHR-1 affiliated with the Gammaproteobacteria class of the Pseudomonadota phylum from a freshwater lake. In YYHR-1, most magnetosome crystals are organized into a long chain aligned along the cell long axis; unusually, a few small superparamagnetic crystals are located at the side of the chain, off the main chain axis. Micromagnetic simulations indicate that magnetostatic interactions among adjacent crystals within a chain reduce the Gibbs energy to enhance chain stability. Genomic analysis suggests that duplication of magnetosome gene clusters may result in off-chain magnetosomes formation. By integrating available genomic data from Gammaproteobacteria, the phylogenetic position of MTB in this class is reassigned here. Our new findings expand knowledge about MTB diversity and magnetosome biomineralization, and deepen understanding of the phylogenetics of the Gammaproteobacteria.

Biosynthesis of magnetosome-nanobody complex in Magnetospirillum gryphiswaldense MSR-1 and a magnetosome-nanobody-based enzyme-linked immunosorbent assay for the detection of tetrabromobisphenol A in water.

In this study, two mutant strains, TBC and TBC+, able to biosynthesize anovel functional magnetosome-nanobody (Nb), were derived from the magnetotactic bacteria Magnetospirillum gryphiswaldense MSR-1. The magnetosome-Nbs biosynthesized by TBC+ containing multi-copies of theNb gene had ahigher binding ability to an environmental pollutant, tetrabromobisphenol A (TBBPA), than those biosynthesized by TBC containing only one copy of theNb gene. The magnetosome-Nbs from TBC+ can effectively bind to TBBPA in solutions with high capacity without being affected by a broad range of NaCl and methanol concentrations as well as pH. Therefore, a magnetosome-Nb-based enzyme-linked immunosorbent assay (ELISA) was developed and optimized for the detection of TBBPA, yielding a half-maximum signal inhibition concentration of 0.23 ng/mL and a limit of detection of 0.025 ng/mL. The assay was used to detect TBBPA in spiked river water samples, giving average recoveries between 90 and 120% and coefficients of variation of2.5-6.3%. The magnetosome-Nb complex could be reused 4 times in ELISA without affecting the performance of the assay. Our results demonstrate the potential of magnetosome-Nbs produced by TBC+ as cost-effective and environment-friendly reagents for immunoassays to detect small molecules in environmental waters.

Glacial‐Interglacial Circulation and Climatic Changes in the South Indian Ocean (Kerguelen Plateau Region) Recorded by Detrital and Biogenic Magnetic Minerals

AbstractThe Southern Ocean (SO) plays a fundamental role in global climate due to the presence of the intense eastward‐flowing Antarctic Circumpolar Current (ACC), one of the most important ocean current systems. The configuration of the frontal systems of the ACC is controlled by the orbital‐ and millennial‐scale variations of the Southern Hemisphere westerly winds (SHWW) and the SO upwelling. However, the reconstruction of paleoclimate and paleocurrent in the SO remains controversial possibly because of the complex interpretation of paleo‐proxies and the regional variations. Here, we present results from rock magnetic measurements and electron microscopic analyses on marine core MD11‐3353 over the past 150 Kyr, which is located in the Polar Front Zone, west of the Kerguelen Plateau. Our data sets indicate that magnetic mineral assemblages in the core are dominated by detrital magnetic minerals mixed with biogenic magnetic minerals (i.e., magnetofossils formed by magnetotactic bacteria) during the interglacial periods. Changes in the detrital magnetic mineral content indicate a strong modulation of the ACC intensity and the SHWW stress at the orbital scale over the last climatic cycle with an enhanced activity during the glacial periods. The increase in magnetofossils content during the interglacial periods indicates an enhanced nutrient supply from the SO upwelling resulting from the southward migration of the Antarctic Polar Front. Our results suggest that the variations of concentration and assemblage of magnetic minerals can be used as faithful proxies for reconstructing ocean circulation and upwelling changes in the South Indian Ocean over the past 150 Kyr.

External magnetic field have significant effects on diversity of magnetotactic bacteria in sediments from Yangtze River, Chagan Lake and Zhalong Wetland in China

Magnetotactic bacteria (MTB) can rapidly relocate to optimal habitats by magnetotaxis, and play an important role in iron biogeochemical cycling. This study aimed to evaluate the contribution of the external magnetostatic field to the diversity of MTB in freshwater sediments from Yangtze River (Changjiang River, CJ), Chagan Lake (CGH) and Zhalong Wetland (ZL). The magnetic field intensity was tightly associated with the community richness of MTB in CJ, whereas it was closely related to the diversity of MTB in CGH and ZL (p < 0.05), elucidating a significant variation in the community composition of MTB. Magnetic exposure time appeared more significant correlation with community richness than diversity for MTB in CJ and CGH (p < 0.05), while an opposite relationship existed in ZL (p < 0.01). Herbaspirillum (93.81–96.48 %) dominated in the sediments of these surfacewatesr regardless of waterbody types, while it shifted to Magnetospirillum in ZL under 100 Gs magnetic field. The network connectivity and stability of MTB deteriorate with the increase of magnetic field intensity. Functional analysis showed that the Two-component system and ABC transporter system of MTB obviously responded to magnetic field intensity and exposure time. Our findings will pave the way to understanding the response mechanism of MTB community in freshwater sediments to the external magnetostatic field.

Experimental analysis of diverse actin-like proteins from various magnetotactic bacteria by functional expression in Magnetospirillum gryphiswaldense.

To efficiently navigate within the geomagnetic field, magnetotactic bacteria (MTB) align their magnetosome organelles into chains, which are organized by the actin-like MamK protein. Although MamK is the most highly conserved magnetosome protein common to all MTB, its analysis has been confined to a small subgroup owing to the inaccessibility of most MTB. Our study takes advantage of a genetically tractable host where expression of diverse MamK orthologs together with a resurrected MamK LUCA and uncharacterized actin-like Mad28 proteins from deep-branching MTB resulted in gradual restoration of magnetosome chains in various mutants. Our results further indicate the existence of species-specific MamK interactors and shed light on the evolutionary relationships of one of the key proteins associated with bacterial magnetotaxis.

Nanosilver Embedded in a Magnetosome Nanoflower to Enhance Antibacterial Activity for Wound Dressing Applications.

The natural biofilm on magnetosomes obtained from the biomineralization of magnetotactic bacteria, which replaced a complex chemical modification process on the surface of Fe3O4, can be used as the organic component and copper(II) ions as the inorganic component to form organic-inorganic nanoflowers in phosphate systems. Characterization by scanning electron microscopy, Fourier transform infrared spectroscopy, and vibrating-sample magnetometry proved that magnetic nanoflowers loaded with silver ions (Ag/MN-Cu×NFs) were successfully fabricated. In vitro antibacterial experiments demonstrated that Ag/MN-Cu×NFs displayed strong antibacterial effects against Escherichia coli and Staphylococcus aureus, with minimum inhibitory concentrations of 10 and 80 μg/mL, respectively. Ag/MN-Cu×NFs, which possessed good biocompatibility as confirmed by cytotoxicity and hemolysis tests, were able to promote wound healing in the face of bacterial infection in vivo without causing toxicity to major organs. Therefore, magnetosomes as a natural carrier have great application potential in the synthesis of multifunctional magnetosomes by direct hybridization with a target substance.

Temporal Convolutional Network-Based Signal Detection for Magnetotactic Bacteria Communication System.

Molecular communication (MC) aims to use signaling molecules as information carriers to achieve communication between biological entities. However, MC systems severely suffer from inter symbol interference (ISI) and external noise, making it virtually difficult to obtain accurate mathematical models. Specifically, the mathematically intractable channel state information (CSI) of MC motivates the deep learning (DL) based signal detection methods. In this paper, a modified temporal convolutional network (TCN) is proposed for signal detection for a special MC communication system which uses magnetotactic bacteria (MTB) as information carriers. Results show that the TCN-based detector demonstrates the best overall performance. In particular, it achieves better bit error rate (BER) performance than sub-optimal maximum a posteriori (MAP) and deep neural network (DNN) based detectors. However, it behaves similarly to the bidirectional long short term memory (BiLSTM) based detector that has been previously proposed and performs worse than the optimal MAP detector. When both BER performance and computational complexity are taken into account, the proposed TCN-based detector outperforms BiLSTM-based detectors. Furthermore, in terms of robustness evaluation, the proposed TCN-based detector outperforms all other DL-based detectors.

An efficient magnetothermal actuation setup for fast heating/cooling cycles or long-term induction heating of different magnetic nanoparticle classes

Alternating magnetic fields (AMFs) in the ∼100 kHz frequency regime cause magnetic nanoparticles (MNPs) to dissipate heat to their nanoscale environment. This mechanism is beneficial for a variety of applications in biomedicine and nanotechnology, such as localized heating of cancer tissue, actuation of drug release, or inducing conformational changes of molecules. However, engineering electromagnetic resonant circuits which generate fields to efficiently heat MNPs over long time scales, remains a challenge. In addition, many applications require fast heating/cooling cycles over ΔT= 5 °C–10 °C to switch the sample between different states. Here, we present a home-built magnetothermal actuation setup maximized in its efficiency to deliver stable AMFs as well as to enable fast heating/cooling cycles of MNP samples. The setup satisfies various demands, such as an elaborate cooling system to control heating of the circuit components as well as of the sample due to inductive losses. Fast cycles of remote sample heating/cooling (up to ±15 °C min−1) as well as long-term induction heating were monitored via contact-free thermal image recording at sub-mm resolution. Next to characterizing the improved hyperthermia setup, we demonstrate its applicability to heat different types of MNPs: ‘nanoflower’-shaped multicore iron oxide nanoparticles, core shell magnetite MNPs, as well as magnetosomes from magnetotactic bacteria (Magnetospirillum gryphiswaldense). MNPs are directly compared in their structure, surface charge, magnetic properties as well as heating response. Our work provides practical guidelines for AMF engineering and the monitoring of MNP heating for biomedical or nano-/biotechnological applications.

Exploring the host range for genetic transfer of magnetic organelle biosynthesis.

Magnetosomes produced by magnetotactic bacteria have great potential for application in biotechnology and medicine due to their unique physicochemical properties and high biocompatibility. Attempts to transfer the genes for magnetosome biosynthesis into non-magnetic organisms have had mixed results. Here we report on a systematic study to identify key components needed for magnetosome biosynthesis after gene transfer. We transfer magnetosome genes to 25 proteobacterial hosts, generating seven new magnetosome-producing strains. We characterize the recombinant magnetosomes produced by these strains and demonstrate that denitrification and anaerobic photosynthesis are linked to the ability to synthesize magnetosomes upon the gene transfer. In addition, we show that the number of magnetosomes synthesized by a foreign host negatively correlates with the guanine-cytosine content difference between the host and the gene donor. Our findings have profound implications for the generation of magnetized living cells and the potential for transgenic biogenic magnetic nanoparticle production.

Novel Magnetotactic Bacteria Strain for Enhanced Aluminium Ions Biosorption

Over the decades, the removal of heavy metals from aqueous solution using biosorbents such as algae, fungi, yeast, and bacteria has remained a challenging task. This paper explores the Al(III) biosorption efficiency of magnetotactic bacteria (MTB) via a new strain called SUM 123 of Alcaligenes sp. The influence of temperature, pH, initial Al(III) concentration, and adsorbent dosage on the biosorption efficiency of MTB is examined. The achieved optimum conditions for Al(III) ions biosorption in the aqueous solution is demonstrated to be 80 mg/L, 12 g/L biosorbent at 25 ºC with pH 5. In this situation, the isolated bacteria attained the maximal Al(III) loading capacity as much as 15.74 mg Al(III)/g (biomass) with 99.53% adsorption. Furthermore, better fitness of “the equilibrium data was provided by the Langmuir isotherm model compared to the Freundlich model. Again, the feasibility, spontaneous and endothermic nature of the biosorption process at 10-40ºC were validated by the evaluated thermodynamic parameters (ΔGº, ΔHº and ΔSº). A pseudo second-order kinetic model that fitted the kinetic data was also achieved with a correlation coefficient (R2) value of &gt; 0.993. FTIR spectra manifested the involvement of hydroxyl, amide, and amine groups in Al(III) biosorption process.” TGA displayed the existence of Al(III) adsorption on the cell wall. It is established that the SUM 123 biomass assisted biosorption is a prospective cost-effective method for Al(III) recovery from contaminated waters.

A Review of the Current State of Magnetic Force Microscopy to Unravel the Magnetic Properties of Nanomaterials Applied in Biological Systems and Future Directions for Quantum Technologies.

Magnetism plays a pivotal role in many biological systems. However, the intensity of the magnetic forces exerted between magnetic bodies is usually low, which demands the development of ultra-sensitivity tools for proper sensing. In this framework, magnetic force microscopy (MFM) offers excellent lateral resolution and the possibility of conducting single-molecule studies like other single-probe microscopy (SPM) techniques. This comprehensive review attempts to describe the paramount importance of magnetic forces for biological applications by highlighting MFM's main advantages but also intrinsic limitations. While the working principles are described in depth, the article also focuses on novel micro- and nanofabrication procedures for MFM tips, which enhance the magnetic response signal of tested biomaterials compared to commercial nanoprobes. This work also depicts some relevant examples where MFM can quantitatively assess the magnetic performance of nanomaterials involved in biological systems, including magnetotactic bacteria, cryptochrome flavoproteins, and magnetic nanoparticles that can interact with animal tissues. Additionally, the most promising perspectives in this field are highlighted to make the reader aware of upcoming challenges when aiming toward quantum technologies.

Integrated Microfluidic-Electromagnetic System to Probe Single-Cell Magnetotaxis in Microconfinement.

Magnetotactic bacteria have great potential for use in biomedical and environmental applications due to the ability to direct their navigation with a magnetic field. Applying and accurately controlling a magnetic field within a microscopic region during bacterial magnetotaxis studies at the single-cell level is challenging due to bulky microscope components and the inherent curvilinear field lines produced by commonly used bar magnets. In this paper, a system that integrates microfluidics and electromagnetic coils is presented for generating a linear magnetic field within a microenvironment compatible with microfluidics, enabling magnetotaxis analysis of groups or single microorganisms on-chip. The platform, designed and optimised via finite element analysis, is integrated into an inverted fluorescent microscope, enabling visualisation of bacteria at the single-cell level in microfluidic devices. The electromagnetic coils produce a linear magnetic field throughout a central volume where the microfluidic device containing the magnetotactic bacteria is located. The magnetic field, at this central position, can be accurately controlled from 1 to 10 mT, which is suitable for directing the navigation of magnetotactic bacteria. Potential heating of the microfluidic device from the operating coils was evaluated up to 2.5 A, corresponding to a magnetic field of 7.8 mT, for 10 min. The maximum measured heating was 8.4 °C, which enables analysis without altering the magnetotaxis behaviour or the average swimming speed of the bacteria. Altogether, this work provides a design, characterisation and experimental test of an integrated platform that enables the study of individual bacteria confined in microfluidics, under linear and predictable magnetic fields that can be easily and accurately applied and controlled.