Medical imaging relies on tracer materials to enable accurate visualization and diagnosis of diseases. Magnetic Particle Imaging (MPI) is an innovative tomographic modality that offers exceptional sensitivity and temporal resolution. These characteristics make MPI particularly promising for clinical applications such as real-time vascular and perfusion imaging, tumor detection, and intraoperative guidance. However, MPI performance has so far been limited by the quality of available tracers, as conventional chemical synthesis provides only restricted control over the size, shape, and magnetic properties of iron oxide nanoparticles. Biogenic magnetic nanoparticles, so-called magnetosomes, produced by magnetotactic bacteria, represent a compelling alternative. Magnetosome biosynthesis is fully genetically encoded, enabling the natural formation of magnetite nanoparticles with uniform size and morphology, which is difficult to achieve through chemical synthesis. Moreover, genetic engineering of the bacterial production host allows precise tuning of particle characteristics, including size, shape, and magnetic behavior, to meet specific application requirements. In this study, magnetosomes isolated from different Magnetospirillum gryphiswaldense mutant strains, each biomineralizing particles with distinct core diameters, were systematically evaluated as potential MPI tracers. Magnetic particle spectroscopy (MPS) was used to identify the most promising candidates based on their signal properties. These tracers were subsequently subjected to detailed signal analyses and phantom experiments to directly compare their imaging performance. Our findings demonstrate that genetically tailored magnetosomes can substantially improve MPI signal quality, underscoring their potential as next-generation tracers. This work provides a foundation for the rational design of optimized biogenic nanoparticles to advance preclinical and future clinical MPI applications. STATEMENT OF SIGNIFICANCE: Magnetic Particle Imaging (MPI) is a novel imaging technology with high sensitivity and real-time capabilities, making it highly promising for clinical applications such as blood flow monitoring and tumor detection. The performance of MPI strongly depends on the properties of the tracer materials used. However, producing high-quality tracers through conventional chemical synthesis remains challenging. In this study, we introduce an innovative biological approach by using genetically engineered magnetotactic bacteria to produce uniform magnetic nanoparticles, so-called magnetosomes. This strategy allows precise control of particle size, shape, and magnetic properties, resulting in tracers with superior performance. Our findings pave the way for the development of next-generation MPI tracers, advancing both fundamental research and potential clinical translation.

Expression, purification and biochemical characterization of the periplasmic nitrate reductase NapA from Magnetospirillum gryphiswaldense MSR-1.

Many nanoscale magnetic imaging techniques are constrained by the maximum magnetic field that can be applied during measurements, due to geometrical limitations or interactions with the probe or the detected signal (e.g., electrons). Here, it is demonstrated that sample-integrated metamaterial-inspired magnetic flux concentrators (MFCs) locally amplify magnetic fields, allowing observation of magnetization processes beyond instrumental limits. Micrometer-sized MFCs fabricated directly on the samples are tested in photoemission electron microscopy experiments employing X-ray magnetic circular dichroism as magnetic contrast mechanism. At low applied fields, substantial amplification factors enable observation of magnetization reversal in a chain of magnetite nanoparticles synthesized by magnetotactic bacteria at an applied field of 8mT, substantially smaller than the ∼50mT predicted by simulations in the absence of MFCs. At higher fields, the field enhancement extends the accessible field range by a factor of five, enabling for the first time, imaging of the field-dependent magnetic domain structure evolution of an isolated giant magnetofossil. Finally, we show how MFC geometry and material parameters can be tuned to optimize performance considering sample and experimental constraints, providing a tunable and broadly applicable strategy for extending the accessible field range in a wide variety of nanoscale magnetic imaging techniques.

A novel role for magnetotactic bacterium: Magnetospirillum magneticum AMB-1 prolonged healthy lifespan of Caenorhabditis elegans via regulating ferroptosis.

Acidithiobacillus ferrooxidans, a chemolithoautotrophic iron- and sulfur-oxidizing acidophile, is a key contributor to industrial-scale copper metal bioleaching. These cells naturally produce magnetosomes, and they may serve as an emerging platform for magnetosome bioproduction, as magnetotactic bacteria (MTB) are difficult to cultivate and genetically modify. Here, we manipulated the expression of the endogenous homologues to the magA and mamB genes in A. ferrooxidans, which are implicated in iron transport required for magnetosome synthesis. Modulation of mamB had no impact on cell behavior. Overexpression of magA increased magnetosome formation and magnetic responsiveness, and these effects were attenuated by CRISPRi knockdown of magA. The augmented magnetosome formation in the magA overexpression cells also led to enhanced bioleaching of pyrite, which is weakly paramagnetic, and this could be further enhanced by the addition of an external magnetic field. These results confirm that magA plays a critical role in magnetosome formation in A. ferrooxidans and that the magnetosome expression can be enhanced through genetic engineering. In addition, these results demonstrate the potential to improve metal sulfide bioleaching through manipulation of genes involved in magnetosome formation.

Magnetotactic bacteria (MTB) utilize magnetosomes to align passively with Earth's magnetic field. Magnetic alignment, coupled with flagellar motility and aerotaxis, enables MTB to perform magneto-aerotaxis-a strategy that constrains their movement to a one-dimensional trajectory along geomagnetic field lines, which is believed to optimize their search for low-oxygen niches in aquatic environments. Beyond axially constrained movement, environmental MTB isolates exhibit a hemispherically determined swimming polarity-favoring either magnetic north or south-that has been suggested to facilitate descent into oxygen-depleted zones. However, a systematic and quantitative evaluation of how matching swimming polarity influences navigation toward low-oxygen environments has remained elusive. Here, we employed microcapillary assays to assess the functional significance of polar magneto-aerotaxis in the model organism Magnetospirillum gryphiswaldense. We found that a magnetic field configuration matching the predominant swimming polarity of the population results in an up to fourfold increased peak intensity of the aerotactic band compared to populations with non-matching polarity. Competition assays using fluorescently labeled north- and south-seeking populations confirmed that congruence between swimming polarity and magnetic field orientation markedly improves aerotactic band formation in oxygen gradients. Alongside our main findings, we noted biomagnetism-independent light-induced behavioral responses integrated with aerotaxis, driving collective unidirectional migration along the oxygen gradient. Our results provide quantitative evidence that matching swimming polarity with the magnetic field confers a clear competitive advantage over cells with an incorrect polarity when navigating oxygen gradients. These findings reinforce the role of the geomagnetic field in shaping MTB behavior and highlight the adaptive value of magnetotactic swimming polarity in environmental navigation. Our observation of light‑triggered behavior further suggests the presence of an additional sensing modality complementing magneto‑aerotactic behavior, highlighting the sophisticated sensory capabilities of M.gryphiswaldense.

Magnetosome membranes: A promising biogenic nanomodel for drug-membrane interaction studies

Magnetosome chains biosynthesized by magnetotactic bacteria combine high magnetic responsivity with efficient magnetothermal conversion but face limitations due to fragile assembly and potential biosafety risks. Here, we report a biomimetic Stöber-based encapsulation strategy that preserves the native chain architecture while imparting structural robustness and enhanced safety. The resulting B-MNC exhibit a coercivity (33.6 mT), approximately 5× higher than magnetosomes, 1.4× higher than intact magnetotactic bacteria, and 2.2× higher than chemically synthesized analogs (C-MNC22). Magnetic characterization reveals ideally uniaxial single-domain behavior with a remanence ratio (Mrs/Ms) of 0.5, outperforming magnetosomes (0.35), bacteria (0.46), and C-MNC22 (0.27). Under an alternating magnetic field (144.1kHz, 34.7 kA m-1), aligned B-MNC achieve a specific absorption rate (SAR) of 1749.7W g-1, which is approximately 4.72× greater than purified magnetosomes, enabling rapid and efficient heating. In vitro, silica encapsulation markedly improves colloidal stability and cytocompatibility. Upon magnetic hyperthermia (42°C, 20min), B-MNC induce 71.4% death of MB49 bladder cancer cells versus only 12.4% for bare magnetosomes. This biomimetic assembly preserves the superior magnetic properties of native magnetosome chains while enhancing magnetic hyperthermia efficacy and biostability, establishing B-MNC as a promising platform for safe and effective magnetic cancer therapy.

Magnetotactic bacteria form a highly diverse group of microorganisms, yet early exploration of their diversity was largely centered on the Pseudomonadota. More recently, metagenomic studies have revealed that magnetotaxis, a form of chemotaxis guided by Earth’s magnetic field, is widespread in other deep-branching phyla for which little to no ecological or biological information is available beyond that inferred from their genomes. For most of them, the morphology, ultrastructure and magnetosome chain characteristics responsible for the magnetic guidance remain unknown. While screening extreme environments for novel magnetotactic species, we observed magnetotactic Bdellovibrionota in the anoxic and ferruginous sediments of the Fontaine Goyon spring (France). We characterized their cell morphology and ultrastructure using magnetic enrichment, a single-cell sorting approach, and high-resolution electron microscopy. Cells display the morphology typical of the few predatory bacteria described in this phylum, and biomineralize, on average, five irregularly faceted, bullet-shaped magnetite magnetosomes along the concave side of the cell. Metagenomic analysis of approximately 100 cells revealed a potentially predatory and heterotrophic lifestyle adapted to low-O2 conditions. It also suggests a flexible respiratory metabolism under varying redox conditions, using iron as an alternative terminal electron acceptor. Exploring the diversity of Bdellovibrionota in public databases, we found 21 metagenome-assembled-genomes containing magnetosome genes. None of them harbor the canonical mamK actin-like gene implicated in aligning magnetosomes in described magnetotactic models. Affiliated to an undescribed class, we propose a classification scheme for the magnetotactic Bdellovibrionota species representing the class Bdellonasia class nov., for which no species had been formally described.

Abstract Aim and purpose The present work explores the isolated Magnetotactic bacteria and their magnetic nanoparticles for their biomedical application potential based on their magnetic properties. Findings MTB isolates were obtained from soils of dy lakebeds and different mineral rich mountains of Southern Karnataka, India and best two isolates were characterized by 16 S rDNA sequencing as Klebsiella species AK01 and Priestia species AK02 (NCBI GenBank (PP886460.1 and PP869085.1 respectively). The magnetosomes as nanoparticle packets were isolated and characterized by XRD, Sem-EDAX and FTIR analysis which confirmed complex of Fe and related metal magnetic materials in the system. The nanoparticles were functionalized by glutaraldehyde fixation of commercially available fungal alpha amylase and activity analysis procedures. The immobilization of enzymes was confirmed by FTIR stretches. Using 3D printer, Microfluidic cell mould was prepared which was used further for preparing basic microfluidic system consisting of 3% agarose and starch respectively. The magnetic actuation of microbial flow in the channels was recorded and images were taken. Conclusion The isolated MTB and magnetosome nanoparticles were characterized and latter were functionalized with enzyme and evaluated for actuation and external controls for potential biomedical applications. The potential application of MTB and their nanoparticles has immense potential in various microrobotic vistas of biotechnology and biomedicine. The present work enhances this repertoire of microbial application in bacteria hitherto not reported before.

Three magnetotactic bacteria, designated strains PR-1T, PR-2T and PR-3T, were isolated from seawater collected from the Mediterranean Sea at the Pointe Rouge Marina in Marseille, France. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain PR-1T formed a clade with representatives of the genus Terasakiella, which previously did not include any magnetotactic members. Strains PR-1T shared 97.90% sequence similarity with Terasakiella brassicae B3T. Strains PR-2T and PR-3T were closely related to previously known magnetotactic strains, Magnetovibrio blakemorei MV-1T and Magnetococcus marinus MC-1T, with 16S rRNA gene sequence similarity of 94.40% and 97.39%, respectively. Strain PR-1T is a spirillum that produces two single flagella at each pole; strain PR-2T is a vibrio equipped with a single polar flagellum, while strain PR-3T is roughly spherical, with two sheathed bundles of flagella at a single pole (bilophotrichous). The major cellular fatty acids are C18 : 1 ω7c and C16 : 1 ω7c for strain PR-1T; C18 : 1 ω7c, C16 : 1 ω7c and C16 : 0 for strain PR-2T; and C16 : 1 ω7c and C16 : 0 for strain PR-3T. Based on phenotypic, genotypic and phylogenetic data, all three strains, PR-1T, PR-2T and PR-3T, are considered to represent three novel species. Strain PR-1T belongs to the genus Terasakiella, for which the name Terasakiella magnetica sp. nov. is proposed. The type strain is PR-1T (=TSD-367T=JCM 39464T). Strain PR-2T belongs to the genus Magnetovibrio, for which the name Magnetovibrio massiliensis sp. nov. is proposed. The type strain is PR-2T (=TSD-368T=JCM 39465T). Strain PR-3T belongs to the genus Magnetococcus, for which the name Magnetococcus organivorans sp. nov. is proposed. The type strain is PR-3T (=TSD-369T=JCM 39466T).

The magnetotactic bacterium Magnetospirillum gryphiswaldense MSR-1 synthesizes membrane-enclosed magnetite (Fe3O4) nanocrystals, known as magnetosomes. Owing to their uniform size, purity and superior magnetic properties, magnetosomes represent highly attractive nanomaterials for biotechnological and biomedical applications. However, their bioproduction is limited by demanding cultivation requirements, largely because magnetite biomineralization is highly sensitive to environmental parameters, particularly oxygen. While elevated oxygen concentrations are known to inhibit magnetosome formation, quantitative analyses under defined low-oxygen conditions are scarce. Here, we cultivated MSR-1 in bioreactors under precisely controlled dissolved oxygen (DO) levels and quantified growth behaviour, substrate uptake and magnetosome characteristics. Cells harvested during late exponential growth revealed that magnetite crystal numbers per cell were similar across a wide DO range (0%-5%), whereas crystal sizes decreased with increasing oxygen levels. The data further indicate that oxygen inhibits biomineralization primarily through direct oxidative interference rather than indirect metabolic effects. These findings provide a mechanistic basis for optimizing oxygen control strategies in MTB cultivation and demonstrate that fine-tuning DO levels enables targeted modulation of magnetosome size and properties. This advances both the bioprocess development of high-yield magnetosome production and the application of tailored magnetic nanoparticles in biotechnology and medicine.

Magnetotactic bacteria are microorganisms that can be controlled using a magnetic field. They have potential applications in medicine, robotics, and environmental engineering, yet most species remain uncultured and poorly characterized. In this study, we report the discovery of a new MTB-rich site in the Ogre River, Latvia, and introduce open-source image-based methods that enable rapid and automated analysis of MTB directly from environmental samples. This accessible toolkit expands the methods to study MTB ecology and diversity, offering a robust framework for future ecological and applied microbiology research.

Bacterial-mediated cancer therapy shows therapeutic potentialyetremains constrained by bioavailability and biosafety challenges. Weintroduce a scalable, modular biosurface-engineering platform forfunctionalizing wild-type magnetotactic bacteria (Magnetospirillummagneticum, AMB-1), enabling the integration of diverse materials,including small molecules, polymers, nanoparticles, and metal–organicframeworks. As a proof-of-concept, AMB-1@Fe3+-PDA (polydopamine) exemplifies a bacteria-mediated therapeutic strategy thatmerges tumor-targeted delivery, immunosuppressive tumor microenvironment(TME) reprogramming, and innate immune activation with photothermal-chemodynamictherapy. The Fe3+-PDA coating counteracts deep-tissue immunosuppressionand primes adaptive immunity, while AMB-1 enhances penetration intoresistant TME niches. These mechanisms synergistically suppress aggressive4T1 breast tumor progression, metastasis, and recurrence while establishingimmunological memory. In murine models, two treatment cycles prolongedmedian survival from 45 to 67 days and elicited systemic antitumorimmunity, including abscopal effects targeting untreated distant tumors.This platform establishes a bridge between materials science and syntheticbiology, providing a generalizable blueprint for advancing the clinicaltranslation of engineered bacterial therapies.

Magnetoreception is a remarkable ability found across a diverse range of organisms, including bacteria, birds, fish, insects, and mammals, enabling them to detect and harness the Earth’s geomagnetic field. Recently, the recruitment of biomineralizing ectosymbionts by euglenozoans was evidenced as an ecological strategy for microeukaryotes to acquire this sense. Here, we report a case of magnetosymbiosis involving a ciliate and four populations of endosymbiotic bacteria experiencing genome reduction. Among these bacteria, one group of sulphate-reducing Desulfovibrionales was found to biomineralize bundles of bullet-shaped magnetite crystals. The ciliate’s magnetotaxis mirrors that of free-living magnetotactic bacteria and euglenozoans, enabling efficient navigation in chemically stratified aquatic environments. However, in this case, magnetotaxis arises from an endosymbiotic interaction. Using a combination of optical-, confocal-, electron- and X-ray-based microscopy techniques, together with genomic analyses, these findings demonstrate that magnetosymbiosis can emerge in unicellular eukaryotic lineages through endosymbiotic integration, expanding our understanding of such interactions in aquatic ecosystems. More broadly, this work contributes to the ongoing debate on the origins of magnetoreception in eukaryotes.

ABSTRACT Once regarded as mere contaminants, intratumoral bacteria are now recognized as functional contributors to cancer progression, promoting therapeutic resistance and metastatic dissemination through diverse mechanisms. On the therapeutic front, innovative strategies are reshaping cancer treatment: synthetic microbial consortia (SMC) counteract Fusobacterium nucleatum ‐associated chemoresistance in colorectal cancer, magnetotactic bacteria (MSR‐CPT/APP@LPs) enhance anti‐PD‐1 efficacy by 40% through spatially targeted co‐delivery of chemotherapeutic and immunomodulatory agents, and the Tumor Microbiome Survival Index robustly predicts survival in pancreatic cancer (4‐year area under the curve = 0.781). We further propose an ecological management framework that combines longitudinal microbiome profiling with precision interventions, advocating for causal validation, such as through Mendelian randomization, and standardized clinical translation to fully exploit this emerging dimension of precision oncology.

Magnetic properties driving nitrogen removal improvement in magnetite-enhanced activated sludge: Mechanistic insights and process validation.

Coal fly ash (CFA), a metal-rich byproduct of coal combustion is produced in vast quantities and poses significant ecological risks. CFA also contains abundant technologically relevant metal oxides and trace metals, including rare earth elements (REE), often at higher concentrations than in primary ores. This makes sustainable recovery strategies a major industrial opportunity. Here, green solvent systems were applied to leach metals from CFA, and the resulting leachates were added to cultures of Magnetospirillum gryphiswaldense (MSR1), a model magnetotactic bacterium that biomineralizes iron into membrane-bound magnetic nanoparticles (magnetosomes) and is capable of interacting with non-iron metals through adsorption and biomineralization. Eleven green solvents, including deep eutectic solvents (DES), were tested for extraction efficiency, with six showing performance comparable to a mineral acid control. Copper (Cu) emerged as the primary toxicant to MSR1, prompting selective precipitation with potassium ferrocyanide trihydrate (PFCT) to reduce its concentration. Cu-depleted lactic acid-based leachates supported MSR1 growth and magnetosome formation even without supplemented iron. Nano-XRF and ICP-MS analysis revealed MSR1 interacts with CFA-derived metals, most significantly showing that produced CFA magnetosomes contained a 5.3-6.1-fold increase in Cu compared to controls. As Cu is both a growth inhibitor and a target pollutant, these findings suggest MSR1 may bioaccumulate Cu within magnetosomes as a detoxification strategy. Overall, this study demonstrates a combined chemical-biological route for CFA valorisation, enabling recovery of diverse metals from waste while producing magnetosomes with distinct compositions.

Abstract Deep‐sea rare earth elements and yttrium (REY)‐rich sediments have attracted considerable attention since their discovery in 2011. However, the environmental factors controlling REY enrichment remain poorly understood, largely because paleoceanographic proxies are absent in pelagic clays. This study focused on two sediment cores with an ultra‐enrichment layer of REY (UELR) from the western and southeastern Pacific. Detailed rock magnetic and transmission electron microscope analyses revealed high magnetofossil abundance in the UELR. It is proposed that strong bottom currents triggered intense upwelling, enhancing primary productivity. This, in turn, stimulated both fish and magnetotactic bacteria reproduction, making the strong coupling between magnetofossils and phosphate, mainly from fish bones and teeth, which efficiently absorbed substantial REYs from seawater. Moreover, magnetic parameters related to eolian dust can also indicate REY composition and the enrichment environment. Therefore, environmental magnetism holds significant potential for investigating the mechanisms of deep‐sea REY enrichment.

Magnetotactic bacteria (MTB) possess intrinsic magnetic navigation via chain-organized magnetosomes, enabling targeted transport in complex biological environments. There is a lack of techniques for MTB drug transport evaluation based on precise behavior monitoring. Here, we proposed a nanotesla-level magnetic detection method for dynamic MTB behavior tracing, which has a sensitivity of 21.6 nT/√Hz under ambient conditions, enabling robust signal acquisition even at very low cell density. This capability was realized by a biocompatible microfluidic-quantum sensing platform that couples a diamond nitrogen-vacancy (NV) center probe with a vascular-mimicking microchannel and a microwave antenna. By linking magnetic signal evolution with bacterial motility, three quantitative indicators were identified, including fitting quality, the early-stage growth rate of the magnetic signal, and the peak rate of signal change. These indicators enabled the predictive classification of enrichment dynamics and guided regulation strategies. This label-free, real-time, and biocompatible framework provides a powerful tool for behavior-resolved analysis of MTB and offers a scalable route toward closed-loop, magnetically guided drug delivery.