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

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

Isolation, microscopic and magnetotactic characterization of Magnetospirillum moscoviense MS-24 from Banjosa Lake, Pakistan

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.

Recovery and genome reconstruction of novel magnetotactic Elusimicrobiota from bog soil

Studying the minor part of the uncultivated microbial majority ("rare biosphere") is difficult even with modern culture-independent techniques. The enormity of microbial diversity creates particular challenges for investigating low-abundance microbial populations in soils. Strategies for selective sample enrichment to reduce community complexity can aid in studying the rare biosphere. Magnetotactic bacteria, apart from being a minor part of the microbial community, are also found in poorly studied bacterial phyla and certainly belong to a rare biosphere. The presence of intracellular magnetic crystals within magnetotactic bacteria allows for their significant enrichment using magnetic separation techniques for studies using a metagenomic approach. This work investigated the microbial diversity of a black bog soil and its magnetically enriched fraction. The poorly studied phylum representatives in the magnetic fraction were enriched compared to the original soil community. Two new magnetotactic species, Candidatus Liberimonas magnetica DUR002 and Candidatus Obscuribacterium magneticum DUR003, belonging to different classes of the relatively little-studied phylum Elusimicrobiota, were proposed. Their genomes contain clusters of magnetosome genes that differ from the previously described ones by the absence of genes encoding magnetochrome-containing proteins and the presence of unique Elusimicrobiota-specific genes, termed mae. The predicted obligately fermentative metabolism in DUR002 and lack of flagellar motility in the magnetotactic Elusimicrobiota broadens our understanding of the lifestyles of magnetotactic bacteria and raises new questions about the evolutionary advantages of magnetotaxis. The findings presented here increase our understanding of magnetotactic bacteria, soil microbial communities, and the rare biosphere.

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.

Detection of interphylum transfers of the magnetosome gene cluster in magnetotactic bacteria

Magnetosome synthesis in magnetotactic bacteria (MTB) is regarded as a very ancient evolutionary process that dates back to deep-branching phyla. Magnetotactic bacteria belonging to one of such phyla, Nitrospirota, contain the classical genes for the magnetosome synthesis (e.g., mam, mms) and man genes, which were considered to be specific for this group. However, the recent discovery of man genes in MTB from the Thermodesulfobacteriota phylum has raised several questions about the inheritance of these genes in MTB. In this work, three new man genes containing MTB genomes affiliated with Nitrospirota and Thermodesulfobacteriota, were obtained. By applying reconciliation with these and the previously published MTB genomes, we demonstrate that the last common ancestor of all Nitrospirota was most likely not magnetotactic as assumed previously. Instead, our findings suggest that the genes for magnetosome synthesis were transmitted to the phylum Nitrospirota by horizontal gene transfer (HGT), which is the first case of the interphylum transfer of magnetosome genes detected to date. Furthermore, we provide evidence for the HGT of magnetosome genes from the Magnetobacteriaceae to the Dissulfurispiraceae family within Nitrospirota. Thus, our results imply a more significant role of HGT in the MTB evolution than deemed before and challenge the hypothesis of the ancient origin of magnetosome synthesis.

Identification of sulfate-reducing magnetotactic bacteria via a group-specific 16S rDNA primer and correlative fluorescence and electron microscopy: strategy for culture-independent study

Magnetotactic bacteria (MTB) biomineralize intracellular magnetic nanocrystals and swim along geomagnetic field lines. While few axenic MTB cultures exist, living cells can be separated magnetically from natural environments for analysis. The bacterial universal 27F/1492R primer pair has been used widely to amplify nearly full-length 16S rRNA genes and to provide phylogenetic portraits of MTB communities. However, incomplete coverage and amplification biases inevitably prevent detection of some phylogenetically specific or non-abundant MTB. Here, we propose a new formulation of the upstream 390F primer that we combined with the downstream 1492R primer to specifically amplify 1,100-bp 16S rRNA gene sequences of sulfate-reducing MTB in freshwater sediments from Lake Weiyanghu, Xi'an, northwestern China. With correlative fluorescence in situ hybridization and scanning/transmission electron microscopy, three novel MTB strains (WYHR-2, WYHR-3, and WYHR-4) from the Desulfobacterota phylum were identified phylogenetically and structurally at the single cell level. Strain WYHR-2 produces bullet-shaped magnetosome magnetite, while the other two strains produce both cubic/prismatic greigite and bullet-shaped magnetite. Our results expand knowledge of bacterial diversity and magnetosome biomineralization of sulfate-reducing MTB. We also propose a general strategy for identifying and characterizing uncultured MTB from natural environments. This article is protected by copyright. All rights reserved.

Heating ability of elongated magnetic nanoparticles

Low-frequency hysteresis loops and specific absorption rate (SAR) of various assemblies of elongated spheroidal magnetite nanoparticles have been calculated for a range of particle semiaxis ratios a/b = 1.0-3.0. The SAR of a dilute randomly oriented assembly of magnetite nanoparticles in an alternating magnetic field of moderate frequency, f = 300 kHz, and amplitude H 0 = 100-200 Oe is shown to decrease significantly with an increase in the aspect ratio of nanoparticles. In addition, there is a narrowing and shift of the intervals of optimal particle diameters towards smaller particle sizes. However, the orientation of a dilute assembly of elongated nanoparticles in a magnetic field leads to an almost twofold increase in SAR at the same frequency and amplitude of the alternating magnetic field, the range of optimal particle diameters remaining unchanged. The effect of the magneto-dipole interaction on the SAR of a dilute assembly of oriented clusters of elongated magnetite nanoparticles has also been investigated depending on the volume fraction of nanoparticles in a cluster. It has been found that the SAR of the assembly of oriented clusters decreases by approximately an order of magnitude with an increase in the volume fraction of nanoparticles in a cluster in the range of 0.04-0.2.

Identification and Genomic Characterization of Two Previously Unknown Magnetotactic Nitrospirae

Magnetotactic bacteria (MTB) are a group of microbes that biomineralize membrane-bound, nanosized magnetite (Fe3O4), and/or greigite (Fe3S4) crystals in intracellular magnetic organelle magnetosomes. MTB belonging to the Nitrospirae phylum can form up to several hundreds of Fe3O4 magnetosome crystals and dozens of sulfur globules in a single cell. These MTB are widespread in aquatic environments and sometimes account for a significant proportion of microbial biomass near the oxycline, linking these lineages to the key steps of global iron and sulfur cycling. Despite their ecological and biogeochemical importance, our understanding of the diversity and ecophysiology of magnetotactic Nitrospirae is still very limited because this group of MTB remains unculturable. Here, we identify and characterize two previously unknown MTB populations within the Nitrospirae phylum through a combination of 16S rRNA gene-based and genome-resolved metagenomic analyses. These two MTB populations represent distinct morphotypes (rod-shaped and coccoid, designated as XYR, and XYC, respectively), and both form more than 100 bullet-shaped magnetosomal crystals per cell. High-quality draft genomes of XYR and XYC have been reconstructed, and they represent a novel species and a novel genus, respectively, according to their average amino-acid identity values with respect to available genomes. Accordingly, the names Candidatus Magnetobacterium cryptolimnobacter and Candidatus Magnetomicrobium cryptolimnococcus for XYR and XYC, respectively, were proposed. Further comparative genomic analyses of XYR, XYC, and previously reported magnetotactic Nitrospirae reveal the general metabolic potential of this MTB group in distinct microenvironments, including CO2 fixation, dissimilatory sulfate reduction, sulfide oxidation, nitrogen fixation, or denitrification processes. A remarkably conserved magnetosome gene cluster has been identified across Nitrospirae MTB genomes, indicating its putative important adaptive roles in these bacteria. Taken together, the present study provides novel insights into the phylogenomic diversity and ecophysiology of this intriguing, yet poorly understood MTB group.

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.

Mass collection of magnetotactic bacteria from the permanently stratified ferruginous Lake Pavin, France

Obtaining high biomass yields of specific microorganisms for culture-independent approaches is a challenge faced by scientists studying organism's recalcitrant to laboratory conditions and culture. This difficulty is highly decreased when studying magnetotactic bacteria (MTB) since their unique behaviour allows their enrichment and purification from other microorganisms present in aquatic environments. Here, we use Lake Pavin, a permanently stratified lake in the French Massif Central, as a natural laboratory to optimize collection and concentration of MTB that thrive in the water column and sediments. A method is presented to separate MTB from highly abundant abiotic magnetic particles in the sediment of this crater lake. For the water column, different sampling approaches are compared such as in situ collection using a Niskin bottle and online pumping. By monitoring several physicochemical parameters of the water column, we identify the ecological niche where MTB live. Then, by focusing our sampling at the peak of MTB abundance, we show that the online pumping system is the most efficient for fast recovering of large volumes of water at a high spatial resolution, which is necessary considering the sharp physicochemical gradients observed in the water column. Taking advantage of aerotactic and magnetic MTB properties, we present an efficient method for MTB concentration from large volumes of water. Our methodology represents a first step for further multidisciplinary investigations of the diversity, metagenomic and ecology of MTB populations in Lake Pavin and elsewhere, as well as chemical and isotopic analyses of their magnetosomes.

Unravelling the diversity of magnetotactic bacteria through analysis of open genomic databases

Magnetotactic bacteria (MTB) are prokaryotes that possess genes for the synthesis of membrane-bounded crystals of magnetite or greigite, called magnetosomes. Despite over half a century of studying MTB, only about 60 genomes have been sequenced. Most belong to Proteobacteria, with a minority affiliated with the Nitrospirae, Omnitrophica, Planctomycetes, and Latescibacteria. Due to the scanty information available regarding MTB phylogenetic diversity, little is known about their ecology, evolution and about the magnetosome biomineralization process. This study presents a large-scale search of magnetosome biomineralization genes and reveals 38 new MTB genomes. Several of these genomes were detected in the phyla Elusimicrobia, Candidatus Hydrogenedentes, and Nitrospinae, where magnetotactic representatives have not previously been reported. Analysis of the obtained putative magnetosome biomineralization genes revealed a monophyletic origin capable of putative greigite magnetosome synthesis. The ecological distributions of the reconstructed MTB genomes were also analyzed and several patterns were identified. These data suggest that open databases are an excellent source for obtaining new information of interest.