Magnetotactic bacteria: nanodrivers of the future

The magneto-microbiome: A dataset of the metagenomic distribution of magnetotactic bacteria

Magnetotactic bacteria (MTB) are diverse prokaryotes characterized by their ability to generate biogenic magnetic iron crystals. MTB are ubiquitous across aquatic environments, and growing evidence has indicated they may be present in association with animal microbiomes. Unfortunately, they are difficult to culture in vitro and more studies understanding their biogeographical distribution and ecological roles are needed. To provide data regarding the patterns of diversity and distribution of MTB, we screened the entire Sequence Read Archive (SRA) from the National Center for Biotechnology Information for DNA sequencing reads matching known MTB taxa. The dataset summarizes the count of reads assigned to MTB from more than 26 million SRA accessions comprising approximately 80 petabases (7.98 × 1016) of DNA. More than 396 million DNA sequencing reads were assigned to 214 MTB taxa in 691,086 (2.65 %) SRA accessions. The final dataset can be utilized by researchers to narrow their efforts in examination of both environmental and ecological roles of specific MTB or to identify potential host organisms. These data will be instrumental to further elucidating the importance and utility of these enigmatic bacteria.

Magnetosomes as Potential Nanocarriers for Cancer Treatment

Magnetotactic bacteria (MTBs) and their organelles, magnetosomes, are intriguing options that might fulfill the criteria of using bacterial magnetosomes (BMs). The ferromagnetic crystals contained in BMs can condition the magnetotaxis of MTBs, which is common in water storage facilities. This review provides an overview of the feasibility of using MTBs and BMs as nanocarriers in cancer treatment. More evidence suggests that MTBs and BMs can be used as natural nanocarriers for conventional anticancer medicines, antibodies, vaccine DNA, and siRNA. In addition to improving the stability of chemotherapeutics, their usage as transporters opens the possibilities for the targeted delivery of single ligands or combinations of ligands to malignant tumors. Magnetosome magnetite crystals are different from chemically made magnetite nanoparticles (NPs) because they are strong single-magnetic domains that stay magnetized even at room temperature. They also have a narrow size range and a uniform crystal morphology. These chemical and physical properties are essential for their usage in biotechnology and nanomedicine. Bioremediation, cell separation, DNA or antigen regeneration, therapeutic agents, enzyme immobilization, magnetic hyperthermia, and contrast enhancement of magnetic resonance are just a few examples of the many uses for magnetite-producing MTB, magnetite magnetosomes, and magnetosome magnetite crystals. From 2004 to 2022, data mining of the Scopus and Web of Science databases showed that most research using magnetite from MTB was carried out for biological reasons, such as in magnetic hyperthermia and drug delivery.

Development of a Genetically Encoded Magnetic Platform in Magnetospirillum gryphiswaldense MSR-1 for Downstream Processing of Protein Expression System

Background

Protein downstream processing remains a challenge in protein production, especially in low yields of products, in spite of ensuring effective disruption of cell and separation of target proteins. It is complicated, expensive and time-consuming. Here, we report a novel nano-bio-purification system for producing recombinant proteins of interest with automatic purification from engineered bacteria.

Results

This system employed a complete genetic engineering downstream processing platform for proteins at low expression levels, referred to as a genetically encoded magnetic platform (GEMP). GEMP consists of four elements as follows. (1) A truncated phage lambda lysis cassette (RRz/Rz1) is controllable for lysis of Magnetospirillum gryphiswaldense MSR-1 (host cell). (2) A surface-expressed nuclease (NucA) is to reduce viscosity of homogenate by hydrolyzing long chain nucleic acids. (3) A bacteriogenic magnetic nanoparticle, known as magnetosome, allows an easy separation system in a magnetic field. (4) An intein realizes abscission of products (nanobodies against tetrabromobisphenol A) from magnetosome.

Conclusions

In this work, removal of most impurities greatly simplified the subsequent purification procedure. The system also facilitated the bioproduction of nanomaterials. The developed platform can substantially simplify industrial protein production and reduce its cost.

Biosensors and Drug Delivery in Oncotheranostics Using Inorganic Synthetic and Biogenic Magnetic Nanoparticles

Magnetic nanocarriers have attracted attention in translational oncology due to their ability to be employed both for tumor diagnostics and therapy. This review summarizes data on applications of synthetic and biogenic magnetic nanoparticles (MNPs) in oncological theranostics and related areas. The basics of both types of MNPs including synthesis approaches, structure, and physicochemical properties are discussed. The properties of synthetic MNPs and biogenic MNPs are compared with regard to their antitumor therapeutic efficiency, diagnostic potential, biocompatibility, and cellular toxicity. The comparative analysis demonstrates that both synthetic and biogenic MNPs could be efficiently used for cancer theranostics, including biosensorics and drug delivery. At the same time, reduced toxicity of biogenic particles was noted, which makes them advantageous for in vivo applications, such as drug delivery, or MRI imaging of tumors. Adaptability to surface modification based on natural biochemical processes is also noted, as well as good compatibility with tumor cells and proliferation in them. Advances in the bionanotechnology field should lead to the implementation of MNPs in clinical trials.

In vitro magnetosome remineralization for silver-magnetite hybrid magnetosome biosynthesis and used for healing of the infected wound

Background

Magnetosomes (BMPs) are organelles of magnetotactic bacteria (MTB) that are responsible for mineralizing iron to form magnetite. In addition, BMP is an ideal biomaterial that is widely used in bio- and nano-technological applications, such as drug delivery, tumor detection and therapy, and immunodetection. The use of BMPs to create multifunctional nanocomposites would further expand the range of their applications.

Results

In this study, we firstly demonstrate that the extracted BMP can remineralize in vitro when it is exposed to AgNO₃ solution, the silver ions (Ag⁺) were transported into the BMP biomembrane (MM) and mineralized into a silver crystal on one crystal plane of Fe₃O₄. Resulting in the rapid synthesis of an Ag-Fe₃O₄ hybrid BMP (BMP-Ag). The synergy between the biomembrane, Fe₃O₄ crystal_, and unmineralized iron enabled the remineralization of BMPs at an Ag⁺ concentration ≥ 1.0 mg mL⁻¹. The BMP-Ag displayed good biocompatibility and antibacterial activity. At a concentration of 2.0 mg/mL, the BMP-Ag and biomembrane removed Ag-Fe₃O₄ NPs inhibited the growth of gram-negative and gram-positive bacteria. Thus using BMP-Ag as a wound dressing can effectively enhance the contraction of infected wounds.

Conclusions

This study represents the first successful attempt to remineralize organelles ex vivo, realizing the biosynthesis of hybrid BMP and providing an important advancement in the synthesis technology of multifunctional biological nanocomposites.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01532-4.

Therapeutic Applications of Magnetotactic Bacteria and Magnetosomes: A Review Emphasizing on the Cancer Treatment

Magnetotactic bacteria (MTB) are aquatic microorganisms have the ability to biomineralize magnetosomes, which are membrane-enclosed magnetic nanoparticles. Magnetosomes are organized in a chain inside the MTB, allowing them to align with and traverse along the earth’s magnetic field. Magnetosomes have several potential applications for targeted cancer therapy when isolated from the MTB, including magnetic hyperthermia, localized medication delivery, and tumour monitoring. Magnetosomes features and properties for various applications outperform manufactured magnetic nanoparticles in several ways. Similarly, the entire MTB can be regarded as prospective agents for cancer treatment, thanks to their flagella’s ability to self-propel and the magnetosome chain’s ability to guide them. MTBs are conceptualized as nanobiots that can be guided and manipulated by external magnetic fields and are driven to hypoxic areas, such as tumor sites, while retaining the therapeutic and imaging characteristics of isolated magnetosomes. Furthermore, unlike most bacteria now being studied in clinical trials for cancer treatment, MTB are not pathogenic but might be modified to deliver and express certain cytotoxic chemicals. This review will assess the current and prospects of this burgeoning research field and the major obstacles that must be overcome before MTB can be successfully used in clinical treatments.

Magnetotactic bacteria in vertical sediments of volcanic lakes in NE China appear Alphaproteobacteria dominated distribution regardless of waterbody types

Magnetotactic bacteria (MTB) distribute widely in sediment habitats and play critical roles in iron cycling. Here, the vertical distribution of morphology and phylogenetic diversity of MTB in sediments (0-15 cm) of three lakes (open waterbody, Bailonghu, BL; semi-enclosed waterbody, Yaoquanhu, YQ; enclosed waterbody, Yueyapao, YY) in Wudalianchi volcanic field (China) were investigated. TEM showed the appearance of coccoid, rod-shaped, oval-shaped, and arc-shaped MTB. With the increase of BL sediment depth, the number of rod-shaped and spherical MTB decreased and increased, respectively. High-throughput sequencing indicated that Alphaproteobacterial MTB dominantly thrived in these lakes regardless of waterbody types. In BL and YY, the dominant genus was Magnetospirillum (44.99-70.80%) which showed a peak in the middle layer. In YQ, the genus Magnetospira was dominant in the upper (52.36%) and middle (66.56%) layer and Magnetococcus (69.63%) existed dominantly in the bottom layer. The vertical distribution of MTB in sediments of these lakes decreased first and then increased. Functional analysis showed that ABC transporter and two-component system of MTB changed significantly with the sediment depth. RDA indicated that the distribution of Magnetospirillum was positively associated with sulfide, pH, and TC. These findings will expand our knowledge of the vertical distribution of MTB in volcanic lakes.

Forced Biomineralization: A Review

Biologically induced and controlled mineralization of metals promotes the development of protective structures to shield cells from thermal, chemical, and ultraviolet stresses. Metal biomineralization is widely considered to have been relevant for the survival of life in the environmental conditions of ancient terrestrial oceans. Similar behavior is seen among extremophilic biomineralizers today, which have evolved to inhabit a variety of industrial aqueous environments with elevated metal concentrations. As an example of extreme biomineralization, we introduce the category of "forced biomineralization", which we use to refer to the biologically mediated sequestration of dissolved metals and metalloids into minerals. We discuss forced mineralization as it is known to be carried out by a variety of organisms, including polyextremophiles in a range of psychrophilic, thermophilic, anaerobic, alkaliphilic, acidophilic, and halophilic conditions, as well as in environments with very high or toxic metal ion concentrations. While much additional work lies ahead to characterize the various pathways by which these biominerals form, forced biomineralization has been shown to provide insights for the progression of extreme biomimetics, allowing for promising new forays into creating the next generation of composites using organic-templating approaches under biologically extreme laboratory conditions relevant to a wide range of industrial conditions.

Tumor-targeting inorganic nanomaterials synthesized by living cells

Inorganic nanomaterials (NMs) have shown potential application in tumor-targeting theranostics, owing to their unique physicochemical properties. Some living cells in nature can absorb surrounding ions in the environment and then convert them into nanomaterials after a series of intracellular/extracellular biochemical reactions. Inspired by that, a variety of living cells have been used as biofactories to produce metallic/metallic alloy NMs, metalloid NMs, oxide NMs and chalcogenide NMs, which are usually automatically capped with biomolecules originating from the living cells, benefitting their tumor-targeting applications. In this review, we summarize the biosynthesis of inorganic nanomaterials in different types of living cells including bacteria, fungi, plant cells and animal cells, accompanied by their application in tumor-targeting theranostics. The mechanisms involving inorganic-ion bioreduction and detoxification as well as biomineralization are emphasized. Based on the mechanisms, we describe the size and morphology control of the products via the modulation of precursor ion concentration, pH, temperature, and incubation time, as well as cell metabolism by a genetic engineering strategy. The strengths and weaknesses of these biosynthetic processes are compared in terms of the controllability, scalability and cooperativity during applications. Future research in this area will add to the diversity of available inorganic nanomaterials as well as their quality and biosafety.

Microbe-Mediated Extracellular and Intracellular Mineralization: Environmental, Industrial, and Biotechnological Applications

Microbe-mediated mineralization is ubiquitous in nature, involving bacteria, fungi, viruses, and algae. These mineralization processes comprise calcification, silicification, and iron mineralization. The mechanisms for mineral formation include extracellular and intracellular biomineralization. The mineral precipitating capability of microbes is often harnessed for green synthesis of metal nanoparticles, which are relatively less toxic compared with those synthesized through physical or chemical methods. Microbe-mediated mineralization has important applications ranging from pollutant removal and nonreactive carriers, to other industrial and biomedical applications. Herein, the different types of microbe-mediated biomineralization that occur in nature, their mechanisms, as well as their applications are elucidated to create a backdrop for future research.

Magnetotactic Bacteria and Magnetosomes as Smart Drug Delivery Systems: A New Weapon on the Battlefield with Cancer?

An important direction of research in increasing the effectiveness of cancer therapies is the design of effective drug distribution systems in the body. The development of the new strategies is primarily aimed at improving the stability of the drug after administration and increasing the precision of drug delivery to the destination. Due to the characteristic features of cancer cells, distributing chemotherapeutics exactly to the microenvironment of the tumor while sparing the healthy tissues is an important issue here. One of the promising solutions that would meet the above requirements is the use of Magnetotactic bacteria (MTBs) and their organelles, called magnetosomes (BMs). MTBs are commonly found in water reservoirs, and BMs that contain ferromagnetic crystals condition the magnetotaxis of these microorganisms. The presented work is a review of the current state of knowledge on the potential use of MTBs and BMs as nanocarriers in the therapy of cancer. The growing amount of literature data indicates that MTBs and BMs may be used as natural nanocarriers for chemotherapeutics, such as classic anti-cancer drugs, antibodies, vaccine DNA, and siRNA. Their use as transporters increases the stability of chemotherapeutics and allows the transfer of individual ligands or their combinations precisely to cancerous tumors, which, in turn, enables the drugs to reach molecular targets more effectively.

Unlocking the Potential of Magnetotactic Bacteria as Magnetic Hyperthermia Agents

Magnetotactic bacteria are aquatic microorganisms that internally biomineralize chains of magnetic nanoparticles (called magnetosomes) and use them as a compass. Here it is shown that magnetotactic bacteria of the strain Magnetospirillum gryphiswaldense present high potential as magnetic hyperthermia agents for cancer treatment. Their heating efficiency or specific absorption rate is determined using both calorimetric and AC magnetometry methods at different magnetic field amplitudes and frequencies. In addition, the effect of the alignment of the bacteria in the direction of the field during the hyperthermia experiments is also investigated. The experimental results demonstrate that the biological structure of the magnetosome chain of magnetotactic bacteria is perfect to enhance the hyperthermia efficiency. Furthermore, fluorescence and electron microscopy images show that these bacteria can be internalized by human lung carcinoma cells A549, and cytotoxicity studies reveal that they do not affect the viability or growth of the cancer cells. A preliminary in vitro hyperthermia study, working on clinical conditions, reveals that cancer cell proliferation is strongly affected by the hyperthermia treatment, making these bacteria promising candidates for biomedical applications.

RGD-functionalized magnetosomes are efficient tumor radioenhancers for X-rays and protons

Although chemically synthesized ferro/ferrimagnetic nanoparticles have attracted great attention in cancer theranostics, they lack radio-enhancement efficacy due to low targeting and internalization ability. Herein, we investigated the potential of RGD-tagged magnetosomes, bacterial biogenic magnetic nanoparticles naturally coated with a biological membrane and genetically engineered to express an RGD peptide, as tumor radioenhancers for conventional radiotherapy and proton therapy. Although native and RGD-magnetosomes similarly enhanced radiation-induced damage to plasmid DNA, RGD-magnetoprobes were able to boost the efficacy of radiotherapy to a much larger extent than native magnetosomes both on cancer cells and in tumors. Combined to magnetosomes@RGD, proton therapy exceeded the efficacy of X-rays at equivalent doses. Also, increased secondary emissions were measured after irradiation of magnetosomes with protons versus photons. Our results indicate the therapeutic advantage of using functionalized magnetoparticles to sensitize tumors to both X-rays and protons and strengthen the case for developing biogenic magnetoparticles for multimodal nanomedicine in cancer therapy.

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.

Applications of Magnetotactic Bacteria, Magnetosomes and Magnetosome Crystals in Biotechnology and Nanotechnology: Mini-Review

Magnetotactic bacteria (MTB) biomineralize magnetosomes, which are defined as intracellular nanocrystals of the magnetic minerals magnetite (Fe₃O₄) or greigite (Fe₃S₄) enveloped by a phospholipid bilayer membrane. The synthesis of magnetosomes is controlled by a specific set of genes that encode proteins, some of which are exclusively found in the magnetosome membrane in the cell. Over the past several decades, interest in nanoscale technology (nanotechnology) and biotechnology has increased significantly due to the development and establishment of new commercial, medical and scientific processes and applications that utilize nanomaterials, some of which are biologically derived. One excellent example of a biological nanomaterial that is showing great promise for use in a large number of commercial and medical applications are bacterial magnetite magnetosomes. Unlike chemically-synthesized magnetite nanoparticles, magnetosome magnetite crystals are stable single-magnetic domains and are thus permanently magnetic at ambient temperature, are of high chemical purity, and display a narrow size range and consistent crystal morphology. These physical/chemical features are important in their use in biotechnological and other applications. Applications utilizing magnetite-producing MTB, magnetite magnetosomes and/or magnetosome magnetite crystals include and/or involve bioremediation, cell separation, DNA/antigen recovery or detection, drug delivery, enzyme immobilization, magnetic hyperthermia and contrast enhancement of magnetic resonance imaging. Metric analysis using Scopus and Web of Science databases from 2003 to 2018 showed that applied research involving magnetite from MTB in some form has been focused mainly in biomedical applications, particularly in magnetic hyperthermia and drug delivery.

Bacterial components as naturally inspired nano-carriers for drug/gene delivery and immunization: Set the bugs to work?

Drug delivery is a rapidly growing area of research motivated by the nanotechnology revolution, the ideal of personalized medicine, and the desire to reduce the side effects of toxic anti-cancer drugs. Amongst a bewildering array of different nanostructures and nanocarriers, those examples that are fundamentally bio-inspired and derived from natural sources are particularly preferred. Delivery of vaccines is also an active area of research in this field. Bacterial cells and their components that have been used for drug delivery, include the crystalline cell-surface layer known as "S-layer", bacterial ghosts, bacterial outer membrane vesicles, and bacterial products or derivatives (e.g. spores, polymers, and magnetic nanoparticles). Considering the origin of these components from potentially pathogenic microorganisms, it is not surprising that they have been applied for vaccines and immunization. The present review critically summarizes their applications focusing on their advantages for delivery of drugs, genes, and vaccines.

Enhancing reaction rate in a Pickering emulsion system with natural magnetotactic bacteria as nanoscale magnetic stirring bars

Pickering emulsion is emerging as an advanced platform for catalysis because of the large oil/water interface area for reaction and its superior efficiency. How to enhance the mass transportation within the micro-droplets is the biggest obstacle in further improving the efficiency of the Pickering emulsion system. In this study, we propose and solve this problem for the first time using natural magnetotactic bacteria as nanoscale magnetic stirring bars, which can be encapsulated into each micro-droplet and used to stir the solution to accelerate the mass transportation under an external magnet, and thus significantly enhance the reaction rate of Pickering emulsion. Taking the epoxidation of cyclooctene in the Pickering emulsion system as a demonstration, the reaction rate was enhanced three times with nanoscale magnetic stirring bars compared to that of traditional Pickering emulsion, and was even thirty times higher than that of conventional stirrer-driven biphasic systems. We envision that this strategy will bring biphasic reactions with fundamental innovations toward more green, efficient and sustainable chemistry.

Bio-templated silica composites for next-generation biomedical applications

Silica-based materials have extensive biomedical applications owing to their unique physical, chemical, and biological properties. Recently, increasing studies have examined the mechanisms involved in biosilicification to develop novel, fine-tunable, eco-friendly materials and/or technologies. In this review, we focus on recent developments in bio-templated silica synthesis and relevant applications in drug delivery systems, tissue engineering, and biosensing.