Biocompatibility evaluation of magnetosomes formed by Acidithiobacillus ferrooxidans

Purification, Characterization, and Assessment of Anticancer Activity of Iron Oxide Nanoparticles Biosynthesized by Novel Thermophilic Bacillus tequilensis ASFS1‏

Magnetic nanoparticles (MNPs), particularly iron oxide nanoparticles (IONPs), are a fascinating group of nanoparticles that have been considerably investigated for biomedical applications because of their superparamagnetic properties, biodegradable nature, and biocompatibility. A novel Gram-positive moderately thermophilic bacterial strain, namely Bacillus tequilensis ASFS.1, was isolated and identified. This strain is capable of producing superparamagnetic Fe3O4 nanoparticles and exhibiting magnetotaxis behavior. This strain swimming behavior was investigated under static and dynamic environments, where it behaved very much similar to the magnetotaxis in magnetotactic bacteria. This study is the first report of a bacterium from the Bacillaceae family that has the potential to intracellular biosynthesis of IONPs. MNPs were separated by a magnetic and reproducible method which was designed for the first time for this study. In addition, UV-visible spectrophotometer, Fourier-transform infrared spectroscopy, vibrating sample magnetometer, field emission scanning electron microscopy (FESEM), X-ray diffraction, and thermal gravimetric analysis were utilized to characterize the bio-fabricated magnetite nanoparticles. Analysis of the particle size distribution pattern of the biogenic MNPs by FESEM imaging revealed the size range of 10-100 nm with the size range of 10-40 nm MNPs being the most frequent particles. VSM analysis demonstrated that biogenic MNPs displayed superparamagnetic properties with a high saturation magnetization value of 184 emu/g. After 24 h treatment of 3T3, U87, A549, MCF-7, and HT-29 cell lines with the biogenic MNPs, IC50 values were measured to be 339, 641, 582, 149, and 184 μg mL-1, respectively. This study presents the novel strain ASFS.1 capable of magnetotaxis by the aid of its magnetite nanoparticles and paving information on isolation, characterization, and in vitro cytotoxicity of its MNPs. The MNPs showed promising potential for biomedical applications, obviously subject to additional studies.

Enhanced bioleaching of spent Li-ion batteries using A. ferrooxidans by application of external magnetic field

Recycling spent batteries is increasingly important for the sustainable use of Li-ion batteries (LIBs) and for countering the supply uncertainty of critical raw minerals (Li, Co, and Ni). Bioleaching, which uses microorganisms to extract valuable metals, is both economical and environmentally safe compared to other recycling methods, but its practical application is impaired by slow kinetics. Accelerating the process is a key for bioleaching spent LIBs on an industrial scale. Acidithiobacillus ferrooxidans (A. ferrooxidans), which thrives in extremely low pH conditions, has long been explored for bioleaching of spent LIBs. Metabolism of A. ferrooxidans involves the oxidation of magnetic Fe2+ and produces intracellular magnetic nanoparticles. The possibility of accelerating the leaching kinetics of A. ferrooxidans by the application of an external magnetic field is explored in this work. A weak static magnetic field is applied during the bioleaching of spent LIBs to recover Li, Ni, and Co using A. ferrooxidans. It is determined that 3 mT is the optimal field strength which allows the leaching efficiency of Li to reach 100% after only 2 days of leaching at a pulp density of 3 w/v % while without the external magnetic field, the leaching efficiency is limited to 57% even after 4 days. The leaching efficiency of Ni and Co also increases by nearly three-fold to >80% after 4 days of leaching. The proposed magnetic field-assisted bioleaching of spent LIBs using A. ferrooxidans substantially improves the leaching kinetics and thus the cost-effectiveness of the bioleaching process with minimal environmental impact, hence enabling environment-friendly recycling of raw materials that are increasingly becoming scarce. The positive effect of an external magnetic field on the metabolism of A. ferrooxidans demonstrated in this work provide a new set of tools to engineer the bioleaching process and the possibility for genetic modification of acidophile bacteria, especially targeted for magnetic enhancement.

Phenomic and transcriptomic analyses reveal the sequential synthesis of Fe3O4 nanoparticles in Acidithiobacillus ferrooxidans BYM

IMPORTANCE

As the most important non-magnetotactic magnetosome-producing bacteria, Acidithiobacillus ferrooxidans only requires very mild conditions to produce Fe3O4 nanoparticles, thus conferring greater flexibility and potential application in biomagnetic nanoparticle production. However, the available information cannot explain the mechanism of Fe3O4 nanoparticle formation in A. ferrooxidans. In this study, we applied phenomic and transcriptomic analyses to reveal this mechanism. We found that different treatment condition factors notably affect the phenomic data of Fe3O4 nanoparticle in A. ferrooxidans. Using transcriptomic analyses, the gene network controlling/regulating Fe3O4 nanoparticle biogenesis in A. ferrooxidans was proposed, excavating the candidate hub genes for Fe3O4 nanoparticle formation in A. ferrooxidans. Based on this information, a sequential model for Fe3O4 nanoparticle synthesis in A. ferrooxidans was hypothesized. It lays the groundwork for further clarifying the feature of Fe3O4 nanoparticle synthesis.

Lipid membrane modulated control of magnetic nanoparticles within bacterial systems

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.

Magnetosome yield characteristics modeling of acidithiobacillus ferrooxidans in airlift bioreactor using response surface methodology

Bacterial magnetosomes had been proved to have great application potential in medicine and biotechnology. The objective of the present study was to obtain high yield of magnetosomes from Acidithiobacillus ferrooxidans (A. ferrooxidans) BYM in an airlift bioreactor using response surface methodology (RSM). The magnetosomes from A. ferrooxidans BYM were characterized using a transmission electron microscope and scanning electron microscopy. The maximum magnetosome yield of 0.4267 mg/L was achieved at ventilation capacity of 3.6 L/min and gluconic acid concentration of 10 mmol/L at 25^oC. The correlation coefficient (R²) value of 0.8676 of the obtained model suggested a good correlation between the actual and predicted magnetosome yield. The confirmation experiment confirmed that the actual magnetosome yield of 0.391 mg/L obtained were in agreement with the predicted value of 0.398 mg/L. These results suggested that RSM can be employed to find out the optimum conditions for magnetosome formation in airlift bioreactor.

Biomanufacturing Biotinylated Magnetic Nanomaterial via Construction and Fermentation of Genetically Engineered Magnetotactic Bacteria

Biosynthesis provides a critical way to deal with global sustainability issues and has recently drawn increased attention. However, modifying biosynthesized magnetic nanoparticles by extraction is challenging, limiting its applications. Magnetotactic bacteria (MTB) synthesize single-domain magnetite nanocrystals in their organelles, magnetosomes (BMPs), which are excellent biomaterials that can be biologically modified by genetic engineering. Therefore, this study successfully constructed in vivo biotinylated BMPs in the MTB Magnetospirillum gryphiswaldense by fusing biotin carboxyl carrier protein (BCCP) with membrane protein MamF of BMPs. The engineered strain (MSR−∆F−BF) grew well and synthesized small-sized (20 ± 4.5 nm) BMPs and were cultured in a 42 L fermenter; the yield (dry weight) of cells and BMPs reached 8.14 g/L and 134.44 mg/L, respectively, approximately three-fold more than previously reported engineered strains and BMPs. The genetically engineered BMPs (BMP−∆F−BF) were successfully linked with streptavidin or streptavidin-labelled horseradish peroxidase and displayed better storage stability compared with chemically constructed biotinylated BMPs. This study systematically demonstrated the biosynthesis of engineered magnetic nanoparticles, including its construction, characterization, and production and detection based on MTB. Our findings provide insights into biomanufacturing multiple functional magnetic nanomaterials.

Progress in affinity ligand-functionalized bacterial magnetosome nanoparticles for bio-immunomagnetic separation of HBsAg protein

Efficient Bio-immunomagnetic separation (BIMS) of recombinant hepatitis B surface antigen (rHBsAg) with high binding capacity was studied using affinity ligand immobilized bacterial magnetosome nanoparticles (Magnetospirillum gryphiswaldense strain MSR-1 bacteria) as an immunomagnetic sorbent. Our results showed immunomagnetic adsorption, acted by affinity interactions with the immobilized monoclonal antibody, offered higher antigen adsorption and desorption capacities as compared with the commercially available immunoaffinity sorbents. Four different ligand densities of the Hep-1 monoclonal antibody were examined during covalent immobilization on Pyridyl Disulfide-functionalized magnetosome nanoparticles for HBsAg immunomagnetic separation. The average of adsorption capacity was measured as 3 mg/ml in optimized immunomagnetic sorbent (1.056 mg rHBsAg/ml immunomagneticsorbent/5.5 mg of total purified protein) and 5mg/ml in immunoaffinity sorbent (0.876 mg rHBsAg/ml immunosorbent/5.5 mg total purified protein during 8 runs. Immunomagnetic sorbent demonstrated ligand leakage levels below 3 ng Mab/Ag rHBsAg during 12 consecutive cycles of immunomagnetic separation (IMS). The results suggest that an immunomagnetic sorbent with a lower ligand density (LD = 3 mg Mab/ml matrix) could be the best substitute for the immunosorbent used in affinity purification of r-HBsAg there are significant differences in the ligand density (98.59% (p-value = 0.0182)), adsorption capacity (97.051% (p-value = 0.01834)), desorption capacity (96.06% (p-value = 0.036)) and recovery (98.97% (p-value = 0.0231)). This study indicates that the immunosorbent approach reduces the cost of purification of Hep-1 protein up to 50% as compared with 5 mg Mab/ml immunoaffinity sorbent, which is currently used in large-scale production. As well, these results demonstrate that bacterial magnetosome nanoparticles (BMs) represent a promising alternative product for the economical and efficient immobilization of proteins and the immunomagnetic separation of Biomolecules, promoting innovation in downstream processing.

Production and characterization of naturally occurring antibacterial magnetite nanoparticles from magnetotactic Bacillus sp. MTB17

AIMS

This study envisaged the isolation and characterization of magnetite nanoparticles (MNPs) from magnetotactic bacteria (MTB) and the evaluation of their antibacterial efficacy.

METHODS AND RESULTS

MNPs were extracted from 20 motile but morphologically different MTB, and they were subjected to antibacterial activity assay. These MNPs were found to be highly effective against Vibrio cholerae. MTB17 was considered as the potent MTB strain based on the antibacterial activity. The MNPs of MTB17 were isolated and validated by UV-Visible spectroscopy, particle size analysis, FTIR analysis, and PXRD.

CONCLUSIONS

Isolation and characterization of ~85 nm MNPs from MTB is reported, and it is highly active against all the gram-positive and gram-negative strains tested.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study focuses on a novel use of biogenic magnetite MNPs as an antibacterial agent, which can be further explored using in vivo studies.

Preparation, characterization, and in vitro release kinetics of doxorubicin-loaded magnetosomes

The doxorubicin (DOX) was successfully coupled to the magnetosomes from Acidithiobacillus ferrooxidans (At. ferrooxidans) by genipin bridging. The parameters (magnetosome concentration, DOX concentration, genipin concentration-, and cross-link time) expected for temperature significantly influenced the coupling rate. Bacterial magnetosome-doxorubicin complexes (BMDCs) were characterized by transmission electron microscope (TEM), particle size analyzer and Fourier transform infrared spectroscopy. Results indicated that BMDCs exhibited a mean particle size of 83.98 mm and displayed a negative charge. The chemical reaction occurring between CO and NH group and the physical adsorption predominated by electrostatic interaction were found to involve in coupling. BMDCs can release 40% of DOX in simulated gastrointestinal conditions within 38 h. Kinetic models including Higuchi, Korsmeyer-Peppas, Zero order, First order, Hixon-Crowell, Baker-Lonsdale, and Weibull and Gompertz were utilized to explore the release mechanism of DOX from BMDCs. All models were found to fit well (r² ≥ 0.8144) with the release data and the Gompertz was the best fit model (r² = 0.9742), implying that the complex mechanisms involving Fickian and Gompertz diffusion contributed to the release. These findings suggested that magnetosomes from At. ferrooxidans have great potential applications in biomedical and clinical fields as the carrier of target drug delivery systems in the future.

A comprehensive assessment of the biocompatibility of Magnetospirillum gryphiswaldense MSR-1 bacterial magnetosomes in vitro and in vivo

Bacterial magnetosomes (BMs) are iron oxide nanoparticles synthesized naturally by magnetotactic bacteria, made up of nano-sized inorganic crystals enclosed by a lipid bilayer membrane. Due to several superior characteristics, such as the narrow size distribution, uniform morphology, high purity and crystallinity, single magnetic domain as well as easy surface modification, increasing biomedical and biotechnological applications of BMs have been developed. The attracted wide attentions raise the urge for the evaluation of safety and toxicity. In this work, we performed a rather comprehensive and systematic assessment of in vitro and in vivo toxicity of BMs from MSR-1, including the cytotoxicity, mice bodyweights, blood test, organ coefficients, inflammation, and hemocompatibility study. We found that BMs have good biocompatibility except for influences on the immune response as demonstrated by enhanced activation of the complement system and inhibition of lymphocyte proliferation when used with an excessive concentration. BMs induced the production of reactive oxygen species (ROS) in macrophages at a dose-dependent manner but did not cause cell membrane damage and cell cycle arrest until the concentration is approximately 40 times the clinical dosage. We anticipate our work will guide modifications of BMs and expand their future applications.

Magnetotactic Bacteria and Magnetosomes: Basic Properties and Applications

Magnetotactic bacteria (MTB) belong to several phyla. This class of microorganisms exhibits the ability of magneto-aerotaxis. MTB synthesize biominerals in organelle-like structures called magnetosomes, which contain single-domain crystals of magnetite (Fe3O4) or greigite (Fe3S4) characterized by a high degree of structural and compositional perfection. Magnetosomes from dead MTB could be preserved in sediments (called fossil magnetosomes or magnetofossils). Under certain conditions, magnetofossils are capable of retaining their remanence for millions of years. This accounts for the growing interest in MTB and magnetofossils in paleo- and rock magnetism and in a wider field of biogeoscience. At the same time, high biocompatibility of magnetosomes makes possible their potential use in biomedical applications, including magnetic resonance imaging, hyperthermia, magnetically guided drug delivery, and immunomagnetic analysis. In this review, we attempt to summarize the current state of the art in the field of MTB research and applications.

Biocompatibility of Bacterial Magnetosomes as MRI Contrast Agent: A Long-Term In Vivo Follow-Up Study

Derived from magnetotactic bacteria (MTB), magnetosomes consist of magnetite crystals enclosed within a lipid bilayer membrane and are known to possess advantages over artificially synthesized nanoparticles because of the narrow size distribution, uniform morphology, high purity and crystallinity, single magnetic domain, good biocompatibility, and easy surface modification. These unique properties have increasingly attracted researchers to apply bacterial magnetosomes (BMs) in the fields of biology and medicine as MRI imaging contrast agents. Due to the concern of biosafety, a long-term follow-up of the distribution and clearance of BMs after entering the body is necessary. In this study, we tracked changes of BMs in major organs of mice up to 135 days after intravenous injection using a combination of several techniques. We not only confirmed the liver as the well-known targeted organs of BMs, but also found that BMs accumulated in the spleen. Besides, two major elimination paths, as well as the approximate length of time for BMs to be cleared from the mice, were revealed. Together, the results not only confirm that BMs have high biocompatibility, but also provide a long-term in-vivo assessment which may further help to forward the clinical applications of BMs as an MRI contrast agent.

Complete Genome Sequence Analysis of Acidithiobacillus ferrivorans XJFY6S-08 Reveals Environmental Adaptation to Alpine Acid Mine Drainage

The present work reported the complete genome sequence analysis of Acidithiobacillus ferrivorans strain XJFY6S-08 isolated from acid mine drainage in Fuyun copper mine in Xinjiang, China, revealing the potential for extreme environmental adaptation. The strain XJFY6S-08 possesses 3,161,380 bp in length and 56.55% GC content. Genomic analysis revealed that this strain harbors metal-tolerant genes coding for the mer operon, arsRBC operon and a variety of metal assimilation and efflux proteins. Genes coding for K⁺/H⁺ transporting ATPase and the Na⁺/H⁺ antiporter gene nhaA for pH adaptation were identified. The presence of genes associated with various DNA repair enzymes and the synthesis of mycosporine-like amino acids precursor support the UVR resistance mechanisms. The genes related to membrane modifications (ppiBCD, slyD, surA, cfa and fabF) and resistance-nodulation-division (RND) family can play a crucial role in organic solvents tolerance. The strain XJFY6S-08 resists low-temperature conditions by a set of mechanisms such as changes of RNA metabolism, transmembrane transport, compatible solutes and transport, biofilm and EPS formation, chemotaxis and motility and ROS scavenging. These findings can provide important information for further studying the comparative genome and environmental adaptation mechanism of A. ferrivorans.

Biological materials formed by Acidithiobacillus ferrooxidans and their potential applications

A variety of biological materials including schwertmannite, jarosite, iron-sulfur cluster (ISC) and magnetosomes can be produced by Acidithiobacillus ferrooxidans (A. ferrooxidans). Their possible formation mechanisms involved in iron transformation, iron transport, and electron transfer were proposed. The schwertmannite formation usually occurs under the pH of 2.0-3.51, and a lower or higher pH will promote jarosite to be produced. Available Fe2+ in the environment and the carrier proteins that can transport Fe2+ to the intracellular membranes of A. ferrooxidans play a critical role in the synthesis of magnetosomes and ISC. The potential applications of these biological materials were reviewed, including removal of heavy metal by schwertmannite, detoxification of toxic species by jarosite, the transference of electron and ripening the iron sulfur protein by ISC, and biomedical application of magnetosomes. Additionally, some perspectives for the molecular mechanisms of synthesis and regulation of these biomaterials were briefly described.

Magnetosome-anti-Salmonella antibody complex based biosensor for the detection of Salmonella typhimurium

Epidemic Salmonellosis contracted through the consumption of contaminated food substances is a global concern. Thus, simple and effective diagnostic methods are needed. Magnetosome-based biosensors are gaining attention because of their promising features. Here, we developed a biosensor employing a magnetosome-anti-Salmonella antibody complex to detect lipopolysaccharide (somatic "O" antigen) and Salmonella typhimurium in real samples. Magnetosome was extracted from Magnetospirillum sp. RJS1 and characterized by microscopy. The magnetosome samples (1 and 2 mg/mL) were directly conjugated to anti-Salmonella antibody (0.8-200 μg/mL) and confirmed by spectroscopy and zeta potential. The concentrations of magnetosome, antibody and lipopolysaccharide were optimized by ELISA. The 2 mg/mL-0.8 μg/mL magnetosome-antibody complex was optimal for detecting lipopolysaccharide (0.001 μg/mL). Our assay is a cost-effective (60%) and sensitive (50%) method in detection of lipopolysaccharide. The optimized magnetosome-antibody complex was applied to an electrode surface and stabilized using an external magnetic field. Increased resistance confirmed the detection of lipopolysaccharide (at 0.001-0.1 μg/mL) using impedance spectroscopy. Significantly, the R² value was 0.960. Then, the developed prototype biosensor was applied to food and water samples. ELISA confirmed the presence of lipopolysaccharide in homogenized infected samples and cross reactivity assays confirmed the specificity of the biosensor. Further, the biosensor showed low detection limit (10¹ CFU/mL) in water and milk sample demonstrating its sensitivity. Regression coefficient of 0.974 in water and 0.982 in milk was obtained. The magnetosome-antibody complex captured 90% of the S. typhimurium in real samples which was also confirmed in FE-SEM. Thus, the developed biosensor is selective, specific, rapid and sensitive for detection of S. typhimurium.

Effects of Single and Mixed Energy Sources on Intracellular Nanoparticles Synthesized by Acidithiobacillus ferrooxidans

Effective biosynthesis of magnetite nanoparticles using current technology is challenging. We investigated the synthesis of nanoparticles by Acidithiobacillus ferrooxidans grown on ferrous iron, elemental sulphur, and mixtures of both substrates. A comparison of tests with different doping amounts of elemental sulphur in ferrous-containing medium showed that the addition of 0.25 and 0.5 M elemental sulphur to the medium resulted in an increased delay of microbial growth and ferrous iron oxidation. TEM suggested that the ferrous material was an essential energy source for the synthesis of nanoparticles in cells. TEM results indicated that the different ratios of ferrous and sulphur had no significant effect on the morphology of bacteria and the size of nanoparticles. High-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), and X-ray absorption near edge structure (XANES) showed that the nanoparticles were composed of magnetite. For the first time, HRTEM and XANES spectra in-situ characterization was conducted to investigate the nanoparticles that were synthesized by A. ferrooxidans. The findings from this study indicated that the different ratios of ferrous and sulphur had no significant effect on size and shape of nanoparticles synthesized by A. ferrooxidans.

Magnetically targeted photothemal cancer therapy in vivo with bacterial magnetic nanoparticles

The biomineralized bacterial magnetic nanoparticles (BMPs) have been widely studied for biomedical applications with their magnetic properties and a layer of biomembrane. Herein, BMPs were firstly used for magnetically targeted photothermal cancer therapy in vivo. A self-build C-shaped bipolar permanent magnet was used for magnetic targeting though the generation of a high gradient magnetic field within a small target area. For in vitro simulated experiment, BMPs had a high retention rate in magnetically targeted region with different flow rates. In H22 tumor bearing mice, the magnetic targeting induced a 40% increase of BMPs retention in tumor tissues. In vivo photothermal therapy with 808 nm laser irradiation could induce a complete tumor elimination with magnetic targeting. These results indicated that the systematically administrated BMPs with magnetic targeting would be promising for photothermal cancer therapy.

Acidithiobacillus ferrooxidans and its potential application

The widely distributed Acidithiobacillus ferrooxidans (A. ferrooxidans) lives in extremely acidic conditions by fixing CO₂ and nitrogen, and by obtaining energy from Fe²⁺ oxidation with either downhill or uphill electron transfer pathway and from reduced sulfur oxidation. A. ferrooxidans exists as different genomovars and its genome size is 2.89-4.18 Mb. The chemotactic movement of A. ferrooxidans is regulated by quorum sensing. A. ferrooxidans shows weak magnetotaxis due to formation of 15-70 nm magnetite magnetosomes with surface functional groups. The room- and low-temperature magnetic features of A. ferrooxidans are different from other magnetotactic bacteria. A. ferrooxidans has potential for removing sulfur from solids and gases, metals recycling from metal-bearing ores, electric wastes and sludge, biochemical production synthesizing, and metal workpiece machining.

Bacterial magnetosome and its potential application

Bacterial magnetosome, synthetized by magnetosome-producing microorganisms including magnetotactic bacteria (MTB) and some non-magnetotactic bacteria (Non-MTB), is a new type of material comprising magnetic nanocrystals surrounded by a phospholipid bilayer. Because of the special properties such as single magnetic domain, excellent biocompatibility and surface modification, bacterial magnetosome has become an increasingly attractive for researchers in biology, medicine, paleomagnetism, geology and environmental science. This review briefly describes the general feature of magnetosome-producing microorganisms. This article also highlights recent advances in the understanding of the biochemical and magnetic characteristics of bacterial magnetosome, as well as the magnetosome formation mechanism including iron ions uptake, magnetosome membrane formation, biomineralization and magnetosome chain assembly. Finally, this review presents the potential applications of bacterial magnetosome in biomedicine, wastewater treatment, and the significance of mineralization of magnetosome in biology and geology.

Toxicity assessment of magnetosomes in different models

Magnetosomes are nanosized iron oxide particles surrounded by lipid membrane synthesized by magnetotactic bacteria (MTB). Magnetosomes have been exploited for a broad range of biomedical and biotechnological applications. Due to their enormous potential in the biomedical field, its safety assessment is necessary. Detailed research on the toxicity of the magnetosomes was not studied so far. This study focuses on the toxicity assessment of magnetosomes in various models such as Human RBC's, WBC's, mouse macrophage cell line (J774), Onion root tip and fish (Oreochromis mossambicus). The toxicity in RBC models revealed that the RBC's are unaltered up to a concentration of 150 µg/ml, and its morphology was not affected. The genotoxicity studies on WBC's showed that there were no detectable chromosomal aberrations up to a concentration of 100 µg/ml. Similarly, there were no detectable morphological changes observed on the magnetosome-treated J774 cells, and the viability of the cells was above 90% at all the tested concentrations. Furthermore, the magnetosomes are not toxic to the fish (O. mossambicus), as no mortality or behavioural changes were observed in the magnetosome-treated groups. Histopathological analysis of the same reveals no damage in the muscle and gill sections. Overall, the results suggest that the magnetosomes are safe at lower concentration and does not pose any potential risk to the ecosystem.

Genetically tailored magnetosomes used as MRI probe for molecular imaging of brain tumor

We investigate here the potential of single step production of genetically engineered magnetosomes, bacterial biogenic iron-oxide nanoparticles embedded in a lipid vesicle, as a new tailorable magnetic resonance molecular imaging probe. We demonstrate in vitro the specific binding and the significant internalization into U87 cells of magnetosomes decorated with RGD peptide. After injection at the tail vein of glioblastoma-bearing mice, we evidence in the first 2 h the rapid accumulation of both unlabeled and functionalized magnetosomes inside the tumor by Enhanced Permeability and Retention effects. 24 h after the injection, a specific enhancement of the tumor contrast is observed on MR images only for RGD-labeled magnetosomes. Post mortem acquisition of histological data confirms MRI results with more magnetosomes found into the tumor treated with functionalized magnetosomes. This work establishes the first proof-of-concept of a successful bio-integrated production of molecular imaging probe for MRI.

A Natural Bacterium-Produced Membrane-Bound Nanocarrier for Drug Combination Therapy

To minimize the non-specific toxicity of drug combination during cancer therapy, we prepared a new system synthesized from bacteria to deliver the anticancer drugs cytosine arabinoside (Ara-C) and daunorubicin (DNR). In this study, we selected genipin (GP) and poly-l-glutamic acid (PLGA) as dual crosslinkers. Herewith, we demonstrated the preparation, characterization and in vitro antitumor effects of Ara-C and DNR loaded GP-PLGA-modified bacterial magnetosomes (BMs) (ADBMs-P). The results show that this new system is stable and exhibits optimal drug-loading properties. The average diameters of BMs and ADBMs-P were 42.0 ± 8.6 nm and 65.5 ± 8.9 nm, respectively, and the zeta potential of ADBMs-P (-42.0 ± 6.4 mV) was significantly less than that of BMs (-28.6 ± 7.6 mV). The optimal encapsulation efficiency and drug loading of Ara-C were 68.4% ± 9.4% and 32.4% ± 2.9%, respectively, and those of DNR were 36.1% ± 2.5% and 17.9% ± 1.6%. Interestingly, this system also exhibits long-term release behaviour sequentially, without an initial burst release. The Ara-C drug continued to release about 85% within 40 days, while DNR release lasted only for 13 days. Moreover, similar to free drugs, ADBMs-Ps are strongly cytotoxic to cancer cells in vitro (HL-60 cells), with the inhibition rate approximately 96%. This study reveals that this new system has a potential for drug delivery application in the future, especially for combination therapy.

Learning from magnetotactic bacteria: A review on the synthesis of biomimetic nanoparticles mediated by magnetosome-associated proteins

Much interest has gained the biomineralization process carried out by magnetotactic bacteria. These bacteria are ubiquitous in natural environments and share the ability to passively align along the magnetic field lines and actively swim along them. This ability is due to their magnetosome chain, each magnetosome consisting on a magnetic crystal enveloped by a lipid bilayer membrane to which very unique proteins are associated. Magnetotactic bacteria exquisitely control magnetosome formation, making the magnetosomes the ideal magnetic nanoparticle of potential use in many technological applications. The difficulty to scale up magnetosome production has triggered the research on the in vitro production of biomimetic (magnetosome-like) magnetite nanoparticles. In this context, magnetosome proteins are being used to mediate such in vitro magnetite precipitation experiments. The present work reviews the knowledgement on the magnetosome proteins thought to have a role on the in vivo formation of magnetite crystals in the magnetosome, and the recombinant magnetosome proteins used in vitro to form biomimetic magnetite. It also summarizes the data provided in the literature on the biomimetic magnetite nanoparticles obtained from those in vitro experiments.

Optimization of magnetosome production by Acidithiobacillus ferrooxidans using desirability function approach

Present study aimed to resolve the conflict between cell growth and magnetosome formation of Acidithiobacillus ferrooxidans (A. ferrooxidans) in batch experiments by applying response surface methodology (RSM) integrated a desirability function approach. The effects of several operating parameters on cell growth (OD600) and magnetosome production (Cmag) were evaluated. The maximum overall desirability (D) of 0.923 was achieved at iron concentration of 125.07mM, shake speed of 122.37rpm and nitrogen concentration of 2.40g/L. Correspondingly, the OD600 and Cmag were 0.522 and 1.196, respectively. The confirmation experiment confirmed that the optimum OD600 and Cmag obtained were in good agreement with the predicted values. The inductively coupled plasma atomic emission spectrometer (ICP-AES) and transmission electron microscopy (TEM) analyses revealed that the production of magnetosomes could be improved via optimization. X-ray diffraction (XRD) showed the magnetosomes are magnetite. Results indicated that RSM with a desirability function was a useful technique to get the maximum OD600 and Cmag simultaneously.

Magnetotactic bacteria: nanodrivers of the future

Magnetotactic bacteria (MTB) represent a heterogeneous group of Gram-negative aquatic prokaryotes with a broad range of morphological types, including vibrioid, coccoid, rod and spirillum. MTBs possess the virtuosity to passively align and actively swim along the magnetic field. Magnetosomes are the trademark nano-ranged intracellular structures of MTB, which comprise magnetic iron-bearing inorganic crystals enveloped by an organic membrane, and are dedicated organelles for their magnetotactic lifestyle. Magnetosomes endue high and even dispersion in aqueous solutions compared with artificial magnetites, claiming them as paragon nanomaterials. MTB and magnetosomes offer high technological potential in modern science, technology and medicines. This review focuses on the applicability of MTB and magnetosomes in various areas of modern benefits.

Magnetic properties of Acidithiobacillus ferrooxidans

Understanding the magnetic properties of magnetotactic bacteria (MTBs) is of great interest in fields of life sciences, geosciences, biomineralization, biomagnetism, and planetary sciences. Acidithiobacillus ferrooxidans (At. ferrooxidans), obtaining energy through the oxidation of ferrous iron and various reduced inorganic sulfur compounds, can synthesize intracellular magnetite magnetosomes. However, the magnetic properties of such microorganism remain unknown. Here we used transmission electronmicroscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) assay, vibrating sample magnetometer (VSM), magneto-thermogravimetric analysis (MTGA), and low temperature magnetometry to comprehensively investigate the magnetic characteristics of At. ferrooxidans. Results revealed that each cell contained only 1 to 3 magnetite magnetosomes, which were arranged irregularly. The magnetosomes were generally in a stable single-domain (SD) state, but superparamagnetic (SP) magnetite particles were also found. The calcined bacteria exhibited a ferromagnetic behavior with a Curie Temperature of 454 °C and a coercivity of 16.36 mT. Additionally, the low delta ratio (δFC/δZFC=1.27) indicated that there were no intact magnetosome chains in At. ferrooxidans. Our results provided the new insights on the biomineralization of bacterial magnetosomes and magnetic properties of At. ferrooxidans.