RESUMEN
Detecting life has driven research and exploration for centuries, but recent attempts to compile and generate a framework that summarizes life features, aimed to develop strategies for life detection missions beyond planet Earth, have disregarded a key life feature: behavior. Yet, some behaviors such as biomineralization or motility have occasionally been proposed as biosignatures to detect life. Here, we capitalize on a specific taxis' motility behavior, magnetotaxis, to experimentally provide insights in support of behavior as an unambiguous, sensitive biosignature, and magnetic forces as a prescreening option. Using a magnetotactic bacterial species, Magnetospirillum magneticum, we conducted a lab sensitivity experiment comparing PCR with the hanging drop behavioral assay, using a dilution series. The hanging drop behavioral assay visually shows the motility of MTB toward magnetic poles. Our findings reveal that the behavioral assay exhibits higher sensitivity in the detection of M. magneticum when compared to the established PCR protocol. While both methods present similar detection sensitivities at high concentrations, at ≥ 10-7 fold dilutions, the behavioral method proved more sensitive. The behavioral method can detect bacteria even when samples are diluted at 10-9. Comparable results were obtained with environmental samples from the Hula Valley. We propose behavioral cues as valuable biosignatures in the ongoing efforts of life detection in unexplored aquatic habitats on Earth and to stimulate and support discussions about how to detect extant life beyond Earth. Generic and robust behavioral assays can represent a methodological revolution.
Asunto(s)
Magnetospirillum , Magnetospirillum/fisiología , Sensibilidad y Especificidad , Reacción en Cadena de la Polimerasa/métodosRESUMEN
Multicellular magnetotactic bacteria (MMB) have a surprisingly complex multicellular lifestyle. A new study in PLOS Biology combines genomics, microscopy, and isotopic labeling to show that MMB form obligately multicellular consortia of genetically diverse cells with rudimentary division of labor.
Asunto(s)
Bacterias , Bacterias/genética , Bacterias/metabolismo , Magnetospirillum/metabolismo , Magnetospirillum/fisiología , Magnetospirillum/genética , Magnetospirillum/citología , Magnetosomas/metabolismoRESUMEN
While significant advances have been made in exploring and uncovering the promising potential of biomagnetic materials, persistent challenges remain on various fronts, notably in the characterization of individual elements. This study makes use of advanced modes of Magnetic Force Microscopy (MFM) and tailored MFM probes to characterize individual magnetotactic bacteria in different environments. The characterization of these elements posed a significant challenge, as the magnetosomes, besides presenting low magnetic signal, are embedded in bacteria of much larger size. To overcome this, customed Atomic Force Microscopy probes are developed through various strategies, enhancing sensitivity in different environments, including liquids. Furthermore, employing MFM imaging under an in-situ magnetic field provides an opportunity to gather quantitative data regarding the critical fields of these individual chains of nanoparticles. This approach marks a substantial advancement in the field of MFM for biological applications, enabling the detection of magnetosomes under different conditions.
Asunto(s)
Magnetosomas , Microscopía de Fuerza Atómica , Magnetosomas/metabolismo , Magnetosomas/química , Magnetosomas/ultraestructura , Microscopía de Fuerza Atómica/métodos , Magnetospirillum/metabolismo , Campos MagnéticosRESUMEN
Magnetotactic bacteria are a diverse group of microbes that use magnetic particles housed within intracellular lipid-bounded magnetosome organelles to guide navigation along geomagnetic fields. The development of magnetosomes and their magnetic crystals in Magnetospirillum magneticum AMB-1 requires the coordinated action of numerous proteins. Most proteins are thought to localize to magnetosomes during the initial stages of organelle biogenesis, regardless of environmental conditions. However, the magnetite-shaping protein Mms6 is only found in magnetosomes that contain magnetic particles, suggesting that it might conditionally localize after the formation of magnetosome membranes. The mechanisms for this unusual mode of localization to magnetosomes are unclear. Here, using pulse-chase labeling, we show that Mms6 translated under non-biomineralization conditions translocates to pre-formed magnetosomes when cells are shifted to biomineralizing conditions. Genes essential for magnetite production, namely mamE, mamM, and mamO, are necessary for Mms6 localization, whereas mamN inhibits Mms6 localization. MamD localization was also investigated and found to be controlled by similar cellular factors. The membrane localization of Mms6 is dependent on a glycine-leucine repeat region, while the N-terminal domain of Mms6 is necessary for retention in the cytosol and impacts conditional localization to magnetosomes. The N-terminal domain is also sufficient to impart conditional magnetosome localization to MmsF, altering its native constitutive magnetosome localization. Our work illuminates an alternative mode of protein localization to magnetosomes in which Mms6 and MamD are excluded from magnetosomes by MamN until biomineralization initiates, whereupon they translocate into magnetosome membranes to control the development of growing magnetite crystals.IMPORTANCEMagnetotactic bacteria (MTB) are a diverse group of bacteria that form magnetic nanoparticles surrounded by membranous organelles. MTB are widespread and serve as a model for bacterial organelle formation and biomineralization. Magnetosomes require a specific cohort of proteins to enable magnetite formation, but how those proteins are localized to magnetosome membranes is unclear. Here, we investigate protein localization using pulse-chase microscopy and find a system of protein coordination dependent on biomineralization-permissible conditions. In addition, our findings highlight a protein domain that alters the localization behavior of magnetosome proteins. Utilization of this protein domain may provide a synthetic route for conditional functionalization of magnetosomes for biotechnological applications.
Asunto(s)
Proteínas Bacterianas , Magnetosomas , Magnetospirillum , Magnetospirillum/genética , Magnetospirillum/metabolismo , Magnetosomas/metabolismo , Magnetosomas/genética , Proteínas Bacterianas/metabolismo , Proteínas Bacterianas/genética , Regulación Bacteriana de la Expresión Génica , Transporte de ProteínasRESUMEN
We report the successful fabrication of a pharmaceutical cellular bank (PCB) containing magnetotactic bacteria (MTB), which belong to the Magnetospirillum gryphiswaldense MSR1 species. To produce such PCB, we amplified MTB in a minimal growth medium essentially devoid of other heavy metals than iron and of CMR (Carcinogenic, mutagenic and reprotoxic) products. The PCB enabled to acclimate MTB to such minimal growth conditions and then to produce highly pure magnetosomes composed of more than 99.9% of iron. The qualification of the bank as a PCB relies first on a preserved identity of the MTB compared with the original strain, second on genetic bacterial stability observed over 100 generations or under cryo-preservation for 16 months, third on a high level of purity highlighted by an absence of contaminating microorganisms in the PCB. Furthermore, the PCB was prepared under high-cell load conditions (9.108 cells/mL), allowing large-scale bacterial amplification and magnetosome production. In the future, the PCB could therefore be considered for commercial as well as research orientated applications in nanomedicine. We describe for the first-time conditions for setting-up an effective pharmaceutical cellular bank preserving over time the ability of certain specific cells, i.e. Magnetospirillum gryphiswaldense MSR1 MTB, to produce nano-minerals, i.e. magnetosomes, within a pharmaceutical setting.
Asunto(s)
Magnetosomas , Magnetospirillum , Magnetospirillum/genética , Hierro , Preparaciones Farmacéuticas , Proteínas Bacterianas/genéticaRESUMEN
Nitric oxide (NO) plays an essential role as signaling molecule in regulation of eukaryotic biomineralization, but its role in prokaryotic biomineralization is unknown. Magnetospirillum gryphiswaldense MSR-1, a model strain for studies of prokaryotic biomineralization, has the unique ability to form magnetosomes (magnetic organelles). We demonstrate here that magnetosome biomineralization in MSR-1 requires the presence of NsrRMg (an NO sensor) and a certain level of NO. MSR-1 synthesizes endogenous NO via nitrification-denitrification pathway to activate magnetosome formation. NsrRMg was identified as a global transcriptional regulator that acts as a direct activator of magnetosome gene cluster (MGC) and nitrification genes but as a repressor of denitrification genes. Specific levels of NO modulate DNA-binding ability of NsrRMg to various target promoters, leading to enhancing expression of MGC genes, derepressing denitrification genes, and repressing nitrification genes. These regulatory functions help maintain appropriate endogenous NO level. This study identifies for the first time the key transcriptional regulator of major MGC genes, clarifies the molecular mechanisms underlying NsrR-mediated NO signal transduction in magnetosome formation, and provides a basis for a proposed model of the role of NO in the evolutionary origin of prokaryotic biomineralization processes.
Asunto(s)
Proteínas Bacterianas , Magnetosomas , Magnetospirillum , Proteínas Bacterianas/metabolismo , Magnetosomas/genética , Magnetosomas/metabolismo , Magnetospirillum/genética , Magnetospirillum/metabolismo , Óxido Nítrico/metabolismo , Nitrógeno/metabolismoRESUMEN
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.
Asunto(s)
Magnetosomas , Magnetospirillum , Magnetospirillum/genética , Magnetosomas/genética , Magnetosomas/química , Biotecnología , Fenómenos Magnéticos , Especificidad del Huésped , Proteínas BacterianasRESUMEN
IMPORTANCE: 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.
Asunto(s)
Magnetosomas , Magnetospirillum , Actinas/metabolismo , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Magnetospirillum/genética , Magnetospirillum/metabolismo , Magnetosomas/genética , Magnetosomas/metabolismo , Bacterias/metabolismoRESUMEN
Bacterial magnetosomes synthesized by the magnetotactic bacterium Magnetospirillum magneticum are suitable for biomedical and biotechnological applications because of their high level of chemical purity of mineral with well-defined morphological features and a biocompatible lipid bilayer coating. However, utilizations of native magnetosomes are not sufficient for maximum effectiveness in many applications as the appropriate particle size differs. In this study, a method to control magnetosome particle size is developed for integration into targeted technological applications. The size and morphology of magnetosome crystals are highly regulated by the complex interactions of magnetosome synthesis-related genes; however, these interactions have not been fully elucidated. In contrast, previous studies have shown a positive correlation between vesicle and crystal sizes. Therefore, control of the magnetosome vesicle size is tuned by modifying the membrane lipid composition. Exogenous phospholipid synthesis pathways have been genetically introduced into M. magneticum. The experimental results show that these phospholipids altered the properties of the magnetosome membrane vesicles, which yielded larger magnetite crystal sizes. The genetic engineering approach presented in this study is shown to be useful for controlling magnetite crystal size without involving complex interactions of magnetosome synthesis-related genes.
Asunto(s)
Nanopartículas de Magnetita , Magnetosomas , Magnetospirillum , Óxido Ferrosoférrico/química , Proteínas Bacterianas/metabolismo , Magnetosomas/genética , Magnetosomas/química , Magnetosomas/metabolismo , Magnetospirillum/genética , Magnetospirillum/metabolismo , Bacterias/metabolismo , Lípidos/análisisRESUMEN
At currently, approximately 70 species of magnetotactic bacteria have been identified; thus, there is an urgent need to identify more magnetotactic bacteria from diverse environmental sources with potential applications in industry and biotechnology. To the best of our knowledge, this is the first magnetotactic bacterial strain discovered in Pakistan. The first magnetotactic bacteria, Magnetospirillum moscoviense MS-24, was isolated from Banjosa Lake (Rawalakot), Pakistan, in the current investigation. Magnetospirillum moscoviense MS-24 was screened using the Racetrack method. The Magnetospirillum moscoviense MS-24 were physically characterised using Atomic Force Microscopy, High-Resolution Scanning Electron Microscopy, and Transmission Electron Microscopy. The current study used microscopy to illustrate the shape of bacteria and to find a very obvious chain of magnetosomes within the bacterial cell. The Magnetospirillum moscoviense MS-24 measured about 4 ± 0.04 µm in length and 600 ± 0.02 nm in diameter. The microfluidic chip experiments were also used to detect magnetotaxis behaviour in bacteria.
Asunto(s)
Magnetosomas , Magnetospirillum , Lagos , Pakistán , Magnetosomas/ultraestructura , BacteriasRESUMEN
Magnetotactic bacteria (MTB) are receiving attention for heavy metal biotreatment due to their potential for biosorption with heavy metals and the capability of the magnetic recovery. In this study, we investigated the characteristics of Cr(VI) bioreduction and biosorption by an MTB isolate, Magnetospirillum gryphiswaldense MSR-1, which has a higher growth rate and wider reflexivity in culture conditions. Our results demonstrated that the MSR-1 strain could remove Cr(VI) up to the concentration of 40 mg L-1 and with an optimal activity at neutral pH conditions. The magnetosome synthesis existed regulatory mechanisms between Cr(VI) reduction and cell division. The addition of 10 mg L-1 Cr(VI) significantly inhibited cell growth, but the magnetosome-deficient strain, B17316, showed an average specific growth rate of 0.062 h-1 at the same dosage. Cr(VI) reduction examined by the heat-inactivated and resting cells demonstrated that the main mechanism for MSR-1 strain to reduce Cr(VI) was chromate reductase and adsorption, and magnetosome synthesis would enhance the chromate reductase activity. Finally, our results elucidated that the chromate reductase distributes diversely in multiple subcellular components of the MSR-1 cells, including extracellular, membrane-associated, and intracellular cytoplasmic activity; and expression of the membrane-associated chromate reductase was increased after the cells were pre-exposed by Cr(VI).
Asunto(s)
Magnetosomas , Magnetospirillum , Magnetosomas/metabolismo , Magnetosomas/ultraestructura , Cromatos/metabolismo , Magnetospirillum/metabolismo , Magnetospirillum/ultraestructuraRESUMEN
A spiral-shaped, highly motile bacterium was isolated from freshwater sulfidic sediment. Strain J10T is a facultative autotroph utilizing sulfide, thiosulfate, and sulfur as the electron donors in microoxic conditions. Despite high 16S rRNA gene sequence sequence identity to Magnetospirillum gryphiswaldense MSR-1 T (99.6 %), digital DNA-DNA hybridisation homology and average nucleotide identity between the two strains was of the different species level (25 % and 83 %, respectively). Strain J10T is not magnetotactic. The DNA G + C content of strain J10T is 61.9 %. The predominant phospholipid ester-linked fatty acids are C18:1ω7, C16:1ω7, and C16:0. Strain J10T (=DSM 23205 T = VKM B-3486 T) is the first strain of the genus Magnetospirillum showing lithoautotrophic growth and is proposed here as a novel species, Magnetospirillum sulfuroxidans sp. nov. In addition, we propose to establish a framework for distinguishing genera and families within the order Rhodospirillales based on phylogenomic analysis using the threshold values for average amino acid identity at Ì´ 72 % for genera and Ì´ 60 % for families. According to this, we propose to divide the existing genus Magnetospirillum into three genera: Magnetospirillum, Paramagnetospirillum, and Phaeospirillum, constituting a separate family Magnetospirillaceae fam. nov. in the order Rhodospirillales. Furthermore, phylogenomic data suggest that this order should accomodate six more new family level groups including Magnetospiraceae fam. nov., Magnetovibrionaceae fam. nov., Dongiaceae fam. nov., Niveispirillaceae fam. nov., Fodinicurvataceae fam. nov., and Oceanibaculaceae fam. nov.
Asunto(s)
Magnetospirillum , Magnetospirillum/genética , ARN Ribosómico 16S/genética , ADN Bacteriano/genética , Filogenia , Ácidos Grasos/química , Fosfolípidos/química , Análisis de Secuencia de ADN , Técnicas de Tipificación BacterianaRESUMEN
Magnetotactic bacteria (MTB) ubiquitously inhabit the oxic-anoxic interface or anaerobic areas of aquatic environments. MTB biomineralize magnetite or greigite crystals and synthesize an organelle known as magnetosome. This intrinsic ability of MTB allows them to accumulate iron to levels 100-1000 times higher than those in non-magnetotactic bacteria (non-MTB). Therefore, MTB considerably contributes to the global iron cycle as primary iron suppliers in the aquatic environmental food chain. However, to the best of our knowledge, there have been no reports describing the effects of trophic interactions between MTB and their protist grazers on the iron distributions in MTB grazers and the extracellular milieu. Herein, we evaluated the effects of MTB grazing using a model species of protist (Tetrahymena pyriformis) and a model species of MTB (Magnetospirillum magneticum AMB-1). MTB-fed T. pyriformis exhibited a magnetic response and contained magnetite crystals in their vacuoles. Fluorescence imaging using a ferrous ion-specific fluorescent dye revealed that the cellular ferrous ion content was five times higher in MTB-fed T. pyriformis than in non-MTB grazers. Moreover, soluble iron concentrations in the spent media increased with time during MTB predation. This study provides experimental evidence to delineate the importance of trophic interactions of MTB on iron distributions.
Asunto(s)
Magnetosomas , Magnetospirillum , Óxido Ferrosoférrico/análisis , Magnetosomas/química , Hierro , VacuolasRESUMEN
Hybrid biological robots (biobots) prepared from living cells are at the forefront of micro-/nanomotor research due to their biocompatibility and versatility toward multiple applications. However, their precise maneuverability is essential for practical applications. Magnetotactic bacteria are hybrid biobots that produce magnetosome magnetite crystals, which are more stable than synthesized magnetite and can orient along the direction of earth's magnetic field. Herein, we used Magnetospirillum magneticum strain AMB-1 (M. magneticum AMB-1) for the effective removal of chlorpyrifos (an organophosphate pesticide) in various aqueous solutions by naturally binding with organic matter. Precision control of M. magneticum AMB-1 was achieved by applying a magnetic field. Under a programed clockwise magnetic field, M. magneticum AMB-1 exhibit swarm behavior and move in a circular direction. Consequently, we foresee that M. magneticum AMB-1 can be applied in various environments to remove and retrieve pollutants by directional control magnetic actuation.
Asunto(s)
Óxido Ferrosoférrico , Magnetospirillum , Bacterias/metabolismo , Proteínas Bacterianas/metabolismo , Descontaminación , Magnetospirillum/metabolismo , Robótica/métodosRESUMEN
We report the fabrication of highly pure magnetosomes that are synthesized by magnetotactic bacteria (MTB) using pharmaceutically compatible growth media, i.e., without compounds of animal origin (yeast extracts), carcinogenic, mutagenic, or toxic for reproduction (CMR) products, and other heavy metals than iron. To enable magnetosome medical applications, these growth media are reduced and amended compared with media commonly used to grow these bacteria. Furthermore, magnetosomes are made non-pyrogenic by being extracted from these micro-organisms and heated above 400 °C to remove and denature bacterial organic material and produce inorganic magnetosome minerals. To be stabilized, these minerals are further coated with citric acid to yield M-CA, leading to fully reconstructed chains of magnetosomes. The heating properties and anti-tumor activity of highly pure M-CA are then studied by bringing M-CA into contact with PC3-Luc tumor cells and by exposing such assembly to an alternating magnetic field (AMF) of 42 mT and 195 kHz during 30 min. While in the absence of AMF, M-CA are observed to be non-cytotoxic, they result in a 35% decrease in cell viability following AMF application. The treatment efficacy can be associated with a specific absorption rate (SAR) value of M-CA, which is relatively high in cellular environment, i.e., SARcell = 253 ± 11 W/gFe, while being lower than the M-CA SAR value measured in water, i.e., SARwater = 1025 ± 194 W/gFe, highlighting that a reduction in the Brownian contribution to the SAR value in cellular environment does not prevent efficient tumor cell destruction with these nanoparticles. KEY POINTS : ⢠Highly pure magnetosomes were produced in pharmaceutically compatible growth media ⢠Non-pyrogenic and stable magnetosomes were prepared for human injection ⢠Magnetosomes efficiently destroyed prostate tumor cells in magnetic hyperthermia.
Asunto(s)
Hipertermia Inducida , Magnetosomas , Magnetospirillum , Neoplasias de la Próstata , Masculino , Animales , Humanos , Línea Celular Tumoral , Neoplasias de la Próstata/terapia , BacteriasRESUMEN
Magnetotactic bacteria (MTB) are worth studying because of magnetosome biomineralization. Magnetosome biogenesis in MTB is controlled by multiple genes known as magnetosome-associated genes. Recent advances in bioinformatics provide a unique opportunity for studying functions of magnetosome-associated genes and networks that they are involved in. Furthermore, various types of bioinformatics analyses can also help identify genes associated with magnetosome biogenesis. To predict novel magnetosome-associated genes in the extended CtrA regulon, we analyzed expression data of Magnetospirillum magneticum AMB-1 in the GSE35625 dataset in NCBI GEO. We identified 10 potential magnetosome-associated genes using a combinational approach of differential expression analysis, Gene ontology and Kyoto encyclopedia of genes and genomes pathway enrichment analysis, protein-protein interaction network analysis and weighted gene co-expression network analysis. Meanwhile, we also discovered and compared two co-expression modules that most known magnetosome-associated genes belong to. Our comparison indicated the importance of energy on regulating co-expression module structures for magnetosome biogenesis. At the last stage of our research, we predicted at least four real magnetosome-associated genes out of 10 potential genes, based on a comparison of evolutionary trees between known and potential magnetosome-associated genes. Because of the discovery of common subtrees that the stressed species are enriched in, we proposed a hypothesis that multiple types of environmental stress can trigger magnetosome evolution in different waters, and therefore its evolution can recur at different times in various locations on earth. Overall, our research provides useful information for identifying new MTB species and understanding magnetosome biogenesis.
Asunto(s)
Magnetosomas , Magnetospirillum , Magnetosomas/genética , Magnetosomas/metabolismo , Regulón/genética , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Magnetospirillum/genética , Magnetospirillum/metabolismo , Penicilinas/metabolismoRESUMEN
Horizontal gene transfer is a powerful source of innovations in prokaryotes that can affect almost any cellular system, including microbial organelles. The formation of magnetosomes, one of the most sophisticated microbial mineral-containing organelles synthesized by magnetotactic bacteria for magnetic navigation in the environment, was also shown to be a horizontally transferrable trait. However, the mechanisms determining the fate of such genes in new hosts are not well understood, since non-adaptive gene acquisitions are typically rapidly lost and become unavailable for observation. This likely explains why gene clusters encoding magnetosome biosynthesis have never been observed in non-magnetotactic bacteria. Here, we report the first discovery of a horizontally inherited dormant gene clusters encoding biosynthesis of magnetosomes in a non-magnetotactic phototrophic bacterium Rhodovastum atsumiense. We show that these clusters were inactivated through transcriptional silencing and antisense RNA regulation, but retain functionality, as several genes were able to complement the orthologous deletions in a remotely related magnetotactic bacterium. The laboratory transfer of foreign magnetosome genes to R. atsumiense was found to endow the strain with magnetosome biosynthesis, but strong negative selection led to rapid loss of this trait upon subcultivation, highlighting the trait instability in this organism. Our results provide insight into the horizontal dissemination of gene clusters encoding complex prokaryotic organelles and illuminate the potential mechanisms of their genomic preservation in a dormant state.
Asunto(s)
Magnetosomas , Magnetospirillum , Magnetospirillum/genética , Magnetosomas/genética , Bacterias/genética , Bacterias Gramnegativas/genética , Bacterias Aerobias/genética , Familia de Multigenes , Fenómenos Magnéticos , Proteínas Bacterianas/genéticaRESUMEN
Magnetotactic bacteria Magnetospirillum magneticum AMB-1 have been cultured using three different media: magnetic spirillum growth medium with Wolfe's mineral solution (MSGM + W), magnetic spirillum growth medium without Wolfe's mineral solution (MSGM - W), and flask standard medium (FSM). The influence of the culture medium on the structural, morphological, and magnetic characteristics of the magnetosome chains biosynthesized by these bacteria has been investigated by using transmission electron microscopy, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism. All bacteria exhibit similar average size for magnetosomes, 40-45 nm, but FSM bacteria present slightly longer subchains. In MSGM + W bacteria, Co2+ ions present in the medium substitute Fe2+ ions in octahedral positions with a total Co doping around 4-5%. In addition, the magnetic response of these bacteria has been thoroughly studied as functions of both the temperature and the applied magnetic field. While MSGM - W and FSM bacteria exhibit similar magnetic behavior, in the case of MSGM + W, the incorporation of the Co ions affects the magnetic response, in particular suppressing the Verwey (â¼105 K) and low temperature (â¼40 K) transitions and increasing the coercivity and remanence. Moreover, simulations based on a Stoner-Wolhfarth model have allowed us to reproduce the experimentally obtained magnetization versus magnetic field loops, revealing clear changes in different anisotropy contributions for these bacteria depending on the employed culture medium. Finally, we have related how these magnetic changes affect their heating efficiency by using AC magnetometric measurements. The obtained AC hysteresis loops, measured with an AC magnetic field amplitude of up to 90 mT and a frequency, f, of 149 kHz, reveal the influence of the culture medium on the heating properties of these bacteria: below 35 mT, MSGM - W bacteria are the best heating mediators, but above 60 mT, FSM and MSGM + W bacteria give the best heating results, reaching a maximum heating efficiency or specific absorption rate (SAR) of SAR/f ≈ 12 W g-1 kHz-1.
Asunto(s)
Hipertermia Inducida , Magnetosomas , Magnetospirillum , Magnetospirillum/química , Magnetospirillum/metabolismo , Magnetosomas/química , Fenómenos MagnéticosRESUMEN
Magnetic targeting is one of the most promising approaches for improving the targeting efficiency by which magnetic drug carriers are directed using external magnetic fields to reach their targets. As a natural magnetic nanoparticle (MNP) of biological origin, the magnetosome is a special "organelle" formed by biomineralization in magnetotactic bacteria (MTB) and is essential for MTB magnetic navigation to respond to geomagnetic fields. The magnetic targeting of magnetosomes, however, can be hindered by the aggregation and precipitation of magnetosomes in water and biological fluid environments due to the strong magnetic attraction between particles. In this study, we constructed a magnetosome-like nanoreactor by introducing MTB Mms6 protein into a reverse micelle system. MNPs synthesized by thermal decomposition exhibit the same crystal morphology and magnetism (high saturation magnetization and low coercivity) as natural magnetosomes but have a smaller particle size. The DSPE-mPEG-coated magnetosome-like MNPs exhibit good monodispersion, penetrating the lesion area of a tumor mouse model to achieve magnetic enrichment by an order of magnitude more than in the control groups, demonstrating great prospects for biomedical magnetic targeting applications.