Controlled biomineralization by and applications of magnetotactic bacteria

Hypomagnetic Conditions and Their Biological Action (Review)

The geomagnetic field plays an important role in the existence of life on Earth. The study of the biological effects of (hypomagnetic conditions) HMC is an important task in magnetobiology. The fundamental importance is expanding and clarifying knowledge about the mechanisms of magnetic field interaction with living systems. The applied significance is improving the training of astronauts for long-term space expeditions. This review describes the effects of HMC on animals and plants, manifested at the cellular and organismal levels. General information is given about the probable mechanisms of HMC and geomagnetic field action on living systems. The main experimental approaches are described. We attempted to systematize quantitative data from various studies and identify general dependencies of the magnetobiology effects' value on HMC characteristics (induction, exposure duration) and the biological parameter under study. The most pronounced effects were found at the cellular level compared to the organismal level. Gene expression and protein activity appeared to be the most sensitive to HMC among the molecular cellular processes. The nervous system was found to be the most sensitive in the case of the organism level. The review may be of interest to biologists, physicians, physicists, and specialists in interdisciplinary fields.

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.

Effect of Liquid Crystalline Host on Structural Changes in Magnetosomes Based Ferronematics

The effect of the liquid crystalline host on structural changes in magnetosomes based on ferronematics is studied using the surface acoustic wave (SAW) technique supported by some capacitance and light transmission measurements. The measurement of the attenuation response of SAW propagating along the interface between LC and the piezoelectric substrate is used to study processes of structural changes under magnetic field. The magnetosome nanoparticles of the same volume concentration were added to three different nematic LCs, 5CB, 6CB, and E7. Unlike to undoped LCs, the different responses of SAW attenuation under the influence of magnetic and electric fields in LCs doped with magnetosomes were observed due to characteristic structural changes. The decrease of the threshold field for doped LCs as compared with pure LCs and slight effects on structural changes were registered. The threshold magnetic fields of LCs and composites were determined from capacitance measurements, and the slight shift to lower values was registered for doped LCs. The shift of nematic-isotropic transition was registered from dependencies of SAW attenuation on temperature. The acoustic anisotropy measurement approved the previous supposition about the role of bulk viscosity in used SAW measurements. In addition, capacitance and light transmition investigations supported SAW results and pointed out conclusions about their magnetic field behavior. Obtained results are discussed and confronted with previous ones and coincide well with those observed using acoustic, optical, or dielectric techniques.

Presence of biogenic magnetite in ferromanganese nodules

Transmission electron microscopy (TEM) and rock magnetic study of ferromanganese nodule sample JC120-104B collected from Clarion-Clipperton zone (CCZ) in the eastern Pacific Ocean indicate the presence of biogenic magnetite (magnetofossils). First-order reversal curves (FORCs) and decomposition of isothermal remanent magnetization (IRM) curves were used as the main tool for the characterization of magnetic properties of the bulk magnetic minerals present in the sample. TEM was performed for the direct identification of biogenic magnetic minerals (magnetofossils). The nodule sample has distinctive alternating Mn and Fe-rich layers per micro-X-ray fluorescence data. While diagenetic precipitation of Mn is known for the less oxygenated environment, the presence of biogenic magnetite is also common in the environments where the supply of oxygen is limited. Moreover, the increase in magnetic properties is consistent with the increase in Mn-content, which is related to favourable conditions for Mn precipitation as well as magnetite biomineralization in oxic-suboxic transition zone. Investigations on magnetofossil fingerprints lead to a better understanding of paleoenvironmental conditions involved in the formation and growth of deep-sea ferromanganese nodules.

Introducing a bioelectrochemical method for highly selective enumeration of magnetotactic bacteria

In this study, we employed an electrochemical (potentiometric) method to enumerate magnetotactic bacteria (MTB) during its coupling with iodometric titration to obtain a selective, precise and rapid counting system. Oxygen was considered as an important factor for the orientation and movement of MTB towards the magnet-modified indicator electrode. In the direct potentiometry, a linear correlation was detected between potentiometric response and dissolved oxygen (DO) concentrations. By the increase of the DO concentration, potential difference would increase in the range of 4.0 to 20.0 parts per million (ppm) at different pressure conditions. The reliability of the O₂ bio-sensing feature provides a selective MTB-based cell enumeration methodology based on indirect potentiometric titration. Furthermore, a five-minute H₂-purging resulted in an increase of potentiometric response sensitivity arising from the decrease in DO concentration of the electrolyte solution. Results were also investigated by zeta potential difference, which show the effect of charge density of MTB in presence of DO. Zeta potential was increased proportionally by addition of the MTB population. Regarding the reliability of the suggested method, data obtained by the designed system showed no statistical difference from those obtained by the most common procedure in microbiology for enumeration of bacteria, known as colony forming unit (CFU) method.

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.

Fossilized Bacteria in Fe-Mn-Mineralization: Evidence from the Legrena Valley, W. Lavrion Mine (Greece)

The primary mineralization in the famous Lavrion mine in the Lavreotiki area, Attica (Greece), associated with a granodiorite intrusion of Upper Miocene age and composed of massive sulphide Pb-Zn-Ag ores [sphalerite, pyrite and galena (B.P.G)], has been extensively studied. The present study is focused on thin, hard, dark brown to black Fe-Mn crusts (a few mm to cm in thickness) in the Legrena valley, SW Lavreotiki, aiming to provide new insights on that type of Fe-Mn-mineralization. The scanning electron microscope (SEM)/energy dispersive spectroscopy (EDS) data presented revealed the presence of fine rounded fragments, resembling nodules (up to 200 μm) and fossilized bacteriomorphic Fe-Mn-oxides/hydroxides, within brecciated and foliated zones of carbonate rocks. They exhibit unusual features when compared to the common massive Fe-Mn mineralization with regards the following: (a) the extensive occurrence of bacteriomorphic Fe-oxides/hydroxides and their micro-textures; and (b) the minor elements (K, Na, P, S, Ca, As and Cl). The occurrence of abundant bacteriomophic Fe-Mn-oxides/hydroxides in the samples from the Legrena valley may reflect their catalytic role in the redox reactions during ore-forming processes. The characteristic features of that type of Fe-Mn mineralization seems to be the result of multistage supergene processes superimposed over initial hydrothermal stages. Such a multistage remobilization and precipitation of metals along open space surfaces on karstified carbonates during a subsequent stage of their initial precipitation may be widespread in the Attica region, Greece.

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.

Yield cultivation of magnetotactic bacteria and magnetosomes: A review

Magnetotactic bacteria (MTB) have started to be employed for the biosynthesis of magnetic nanoparticles, due to the rapidly increasing demand for nanoparticles in biomedical, biotechnology and environmental protection. MBT are the group of prokaryotes that have the ability to produce bio-magnetic minerals or bio-magnetic crystals of either magnetite (Fe₃ O₄ ) or greigite (Fe₃ S₄ ) in numerous shapes and size ranges, known as magnetosomes (MS). MS compel MTB to respond to the applied external magnetic field. However, it is extremely difficult to grow MTB and produce high yield of MS under artificial environmental conditions, thus creating a major hurdle to relocate MTB technology from laboratory scale to industrial or commercial level. Therefore, to best of our knowledge this review is the first attempt to highlight existing research developments about the laboratory scale and mass production of MS by MTB. Moreover, the optimum culture media and environmental conditions used for the cultivation of MTB were also considered. Finally, future research is encouraged for the improvement of MS yield which will result in the development of advanced nanotechnology/magnetotechnology.

Manufacturing Man-Made Magnetosomes: High-Throughput In Situ Synthesis of Biomimetic Magnetite Loaded Nanovesicles

A new synthetic method for the production of artificial magnetosomes, i.e., lipid-coated vesicles containing magnetic nanoparticles, is demonstrated. Magnetosomes have considerable potential in biomedical and other nanotechnological applications but current production methods rely upon magnetotactic bacteria which limits the range of sizes and shapes that can be generated as well as the obtainable yield. Here, electrohydrodynamic atomization is utilized to form nanoscale liposomes of tunable size followed by electroporation to transport iron into the nanoliposome core resulting in magnetite crystallization. Using a combination of electron and fluorescence microscopy, dynamic light scattering, Raman spectroscopy, and magnetic susceptibility measurements, it is shown that single crystals of single-phase magnetite can be precipitated within each liposome, forming a near-monodisperse population of magnetic nanoparticles. For the specific conditions used in this study the mean particle size is 58 nm (±8 nm) but the system offers a high degree of flexibility in terms of both the size and composition of the final product.

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.

Correlative electron and fluorescence microscopy of magnetotactic bacteria in liquid: toward in vivo imaging

Magnetotactic bacteria biomineralize ordered chains of uniform, membrane-bound magnetite or greigite nanocrystals that exhibit nearly perfect crystal structures and species-specific morphologies. Transmission electron microscopy (TEM) is a critical technique for providing information regarding the organization of cellular and magnetite structures in these microorganisms. However, conventional TEM can only be used to image air-dried or vitrified bacteria removed from their natural environment. Here we present a correlative scanning TEM (STEM) and fluorescence microscopy technique for imaging viable cells of Magnetospirillum magneticum strain AMB-1 in liquid using an in situ fluid cell TEM holder. Fluorescently labeled cells were immobilized on microchip window surfaces and visualized in a fluid cell with STEM, followed by correlative fluorescence imaging to verify their membrane integrity. Notably, the post-STEM fluorescence imaging indicated that the bacterial cell wall membrane did not sustain radiation damage during STEM imaging at low electron dose conditions. We investigated the effects of radiation damage and sample preparation on the bacteria viability and found that approximately 50% of the bacterial membranes remained intact after an hour in the fluid cell, decreasing to ~30% after two hours. These results represent a first step toward in vivo studies of magnetite biomineralization in magnetotactic bacteria.

Fungal transformation of metallic lead to pyromorphite in liquid medium

Many approaches have been proposed to reduce the toxicity of hazardous substances such as lead in the environment. Several techniques using microorganisms rely on metal removal from solution by non-specific biosorption. However, immobilization of metals through formation of biominerals mediated by metabolic processes offers another solution but which has been given limited attention. In this work, we have investigated lead biomineralization by Paecilomyces javanicus, a fungus isolated from a lead-contaminated soil, in a liquid medium. P. javanicus was able to grow in the presence of metallic lead, supplied as lead shot, and secondary lead minerals were deposited on the lead surfaces as revealed by scanning electron microscopy. Energy dispersive X-ray analysis and X-ray powder diffraction revealed that pyromorphite was formed in the presence of the fungus, but not in abiotic controls. Our results clearly demonstrate that fungal activities can play an important role in lead biocorrosion and biomineralization in an aqueous environment. These findings are relevant to bioremediation approaches for liquid wastes contaminated with lead, or other metals, and also to the immobilization and biorecovery of rare or valuable elements. They also provide further understanding of microbial roles in environmental lead cycling.

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.

Analysis of magnetotactic behavior by swimming assay

Prokaryotic organelles called magnetosomes allow magnetotactic bacteria to navigate along geomagnetic field lines. In this study, we modified a swimming assay commonly used to assess bacterial motility to develop a new method of assessing magnetotactic motility. By this method, the swimming assay was performed in an artificial magnetic field. Magnetotactic bacteria formed a wedge-shaped swimming halo that elongated parallel to the magnetic field. Magnetotactic motility was qualitatively assessed by comparing halo shapes. We termed this method the magnetic swimming assay. On the magnetic swimming assay, the mamK deletion strain formed a shorter halo than the wild type, indicating that the assay sensitively detects differences in magnetotactic motility. Moreover, we isolated two spontaneous magnetotactic motility mutants using magnetic swimming plates. Our findings indicate that the magnetic swimming assay is a useful method for the sensitive analysis of magnetotaxis phenotypes and mutant screening.

Magnetotactic bacteria from extreme environments

Magnetotactic bacteria (MTB) represent a diverse collection of motile prokaryotes that biomineralize intracellular, membrane-bounded, tens-of-nanometer-sized crystals of a magnetic mineral called magnetosomes. Magnetosome minerals consist of either magnetite (Fe3O4) or greigite (Fe3S4) and cause cells to align along the Earth's geomagnetic field lines as they swim, a trait called magnetotaxis. MTB are known to mainly inhabit the oxic-anoxic interface (OAI) in water columns or sediments of aquatic habitats and it is currently thought that magnetosomes function as a means of making chemotaxis more efficient in locating and maintaining an optimal position for growth and survival at the OAI. Known cultured and uncultured MTB are phylogenetically associated with the Alpha-, Gamma- and Deltaproteobacteria classes of the phylum Proteobacteria, the Nitrospirae phylum and the candidate division OP3, part of the Planctomycetes-Verrucomicrobia-Chlamydiae (PVC) bacterial superphylum. MTB are generally thought to be ubiquitous in aquatic environments as they are cosmopolitan in distribution and have been found in every continent although for years MTB were thought to be restricted to habitats with pH values near neutral and at ambient temperature. Recently, however, moderate thermophilic and alkaliphilic MTB have been described including: an uncultured, moderately thermophilic magnetotactic bacterium present in hot springs in northern Nevada with a probable upper growth limit of about 63 °C; and several strains of obligately alkaliphilic MTB isolated in pure culture from different aquatic habitats in California, including the hypersaline, extremely alkaline Mono Lake, with an optimal growth pH of >9.0.

Magnetotactic bacteria, magnetosomes and their application

Magnetotactic bacteria (MTB) are a diverse group of microorganisms with the ability to orient and migrate along geomagnetic field lines. This unique feat is based on specific intracellular organelles, the magnetosomes, which, in most MTB, comprise nanometer-sized, membrane bound crystals of magnetic iron minerals and organized into chains via a dedicated cytoskeleton. Because of the special properties of the magnetosomes, MTB are of great interest for paleomagnetism, environmental magnetism, biomarkers in rocks, magnetic materials and biomineralization in organisms, and bacterial magnetites have been exploited for a variety of applications in modern biological and medical sciences. In this paper, we describe general characteristics of MTB and their magnetic mineral inclusions, but focus mainly on the magnetosome formation and the magnetisms of MTB and bacterial magnetosomes, as well as on the significances and applications of MTB and their intracellular magnetic mineral crystals.

Isolation of obligately alkaliphilic magnetotactic bacteria from extremely alkaline environments

Large numbers of magnetotactic bacteria were discovered in mud and water samples collected from a number of highly alkaline aquatic environments with pH values of ≈ 9.5. These bacteria were helical in morphology and biomineralized chains of bullet-shaped crystals of magnetite and were present in all the highly alkaline sites sampled. Three strains from different sites were isolated and cultured and grew optimally at pH 9.0-9.5 but not at 8.0 and below, demonstrating that these organisms truly require highly alkaline conditions and are not simply surviving/growing in neutral pH micro-niches in their natural habitats. All strains grew anaerobically through the reduction of sulfate as a terminal electron acceptor and phylogenetic analysis, based on 16S rRNA gene sequences, as well as some physiological features, showed that they could represent strains of Desulfonatronum thiodismutans, a known alkaliphilic bacterium that does not biomineralize magnetosomes. Our results show that some magnetotactic bacteria can be considered extremophilic and greatly extend the known ecology of magnetotactic bacteria and the conditions under which they can biomineralize magnetite. Moreover, our results show that this type of magnetotactic bacterium is common in highly alkaline environments. Our findings also greatly influence the interpretation of the presence of nanometer-sized magnetite crystals, so-called magnetofossils, in highly alkaline environments.

Magnetosome chain superstructure in uncultured magnetotactic bacteria

Magnetotactic bacteria produce magnetosomes, which are magnetic particles enveloped by biological membranes, in a highly controlled mineralization process. Magnetosomes are used to navigate in magnetic fields by a phenomenon called magnetotaxis. Two levels of organization and control are recognized in magnetosomes. First, magnetotactic bacteria create a spatially distinct environment within vesicles defined by their membranes. In the vesicles, the bacteria control the size, composition and purity of the mineral content of the magnetic particles. Unique crystal morphologies are produced in magnetosomes as a consequence of this bacterial control. Second, magnetotactic bacteria organize the magnetosomes in chains within the cell body. It has been shown in a particular case that the chains are positioned within the cell body in specific locations defined by filamentous cytoskeleton elements. Here, we describe an additional level of organization of the magnetosome chains in uncultured magnetotactic cocci found in marine and freshwater sediments. Electron microscopy analysis of the magnetosome chains using a goniometer showed that the magnetic crystals in both types of bacteria are not oriented at random along the crystal chain. Instead, the magnetosomes have specific orientations relative to the other magnetosomes in the chain. Each crystal is rotated either 60°, 180° or 300° relative to their neighbors along the chain axis, causing the overlapping of the (1 1 1) and [Formula in text] capping faces of neighboring crystals. We suggest that genetic determinants that are not present or active in bacteria with magnetosomes randomly rotated within a chain must be present in bacteria that organize magnetosomes so precisely. This particular organization may also be used as an indicative biosignature of magnetosomes in the study of magnetofossils in the cases where this symmetry is observed.

Visualization and structural analysis of the bacterial magnetic organelle magnetosome using atomic force microscopy

The unique ability of magnetotactic bacteria to navigate along a geomagnetic field is accomplished with the help of prokaryotic organelles, magnetosomes. The magnetosomes have well-ordered chain-like structures, comprising membrane-enveloped, nano-sized magnetic crystals, and various types of specifically associated proteins. In this study, we applied atomic force microscopy (AFM) to investigate the spatial configuration of isolated magnetosomes from Magnetospirillum magneticum AMB-1 in near-native buffer conditions. AFM observation revealed organic material with a approximately 7-nm thickness surrounding a magnetite crystal. Small globular proteins, identified as magnetosome-associated protein MamA, were distributed on the mica surface around the magnetosome. Immuno-labeling with AFM showed that MamA is located on the magnetosome surface. In vitro experiments showed that MamA proteins interact with each other and form a high molecular mass complex. These findings suggest that magnetosomes are covered with MamA oligomers in near-native environments. Furthermore, nanodissection revealed that magnetosomes are built with heterogeneous structures that comprise the organic layer. This study provides important clues to the supramolecular architecture of the bacterial organelle, the magnetosome, and insight into the function of the proteins localized in the organelle.

Metals, minerals and microbes: geomicrobiology and bioremediation

Microbes play key geoactive roles in the biosphere, particularly in the areas of element biotransformations and biogeochemical cycling, metal and mineral transformations, decomposition, bioweathering, and soil and sediment formation. All kinds of microbes, including prokaryotes and eukaryotes and their symbiotic associations with each other and 'higher organisms', can contribute actively to geological phenomena, and central to many such geomicrobial processes are transformations of metals and minerals. Microbes have a variety of properties that can effect changes in metal speciation, toxicity and mobility, as well as mineral formation or mineral dissolution or deterioration. Such mechanisms are important components of natural biogeochemical cycles for metals as well as associated elements in biomass, soil, rocks and minerals, e.g. sulfur and phosphorus, and metalloids, actinides and metal radionuclides. Apart from being important in natural biosphere processes, metal and mineral transformations can have beneficial or detrimental consequences in a human context. Bioremediation is the application of biological systems to the clean-up of organic and inorganic pollution, with bacteria and fungi being the most important organisms for reclamation, immobilization or detoxification of metallic and radionuclide pollutants. Some biominerals or metallic elements deposited by microbes have catalytic and other properties in nanoparticle, crystalline or colloidal forms, and these are relevant to the development of novel biomaterials for technological and antimicrobial purposes. On the negative side, metal and mineral transformations by microbes may result in spoilage and destruction of natural and synthetic materials, rock and mineral-based building materials (e.g. concrete), acid mine drainage and associated metal pollution, biocorrosion of metals, alloys and related substances, and adverse effects on radionuclide speciation, mobility and containment, all with immense social and economic consequences. The ubiquity and importance of microbes in biosphere processes make geomicrobiology one of the most important concepts within microbiology, and one requiring an interdisciplinary approach to define environmental and applied significance and underpin exploitation in biotechnology.

Complete genome sequence of the chemolithoautotrophic marine magnetotactic coccus strain MC-1

The marine bacterium strain MC-1 is a member of the alpha subgroup of the proteobacteria that contains the magnetotactic cocci and was the first member of this group to be cultured axenically. The magnetotactic cocci are not closely related to any other known alphaproteobacteria and are only distantly related to other magnetotactic bacteria. The genome of MC-1 contains an extensive (102 kb) magnetosome island that includes numerous genes that are conserved among all known magnetotactic bacteria, as well as some genes that are unique. Interestingly, certain genes that encode proteins considered to be important in magnetosome assembly (mamJ and mamW) are absent from the genome of MC-1. Magnetotactic cocci exhibit polar magneto-aerotaxis, and the MC-1 genome contains a relatively large number of identified chemotaxis genes. Although MC-1 is capable of both autotrophic and heterotrophic growth, it does not appear to be metabolically versatile, with heterotrophic growth confined to the utilization of acetate. Central carbon metabolism is encoded by genes for the citric acid cycle (oxidative and reductive), glycolysis, and gluconeogenesis. The genome also reveals the presence or absence of specific genes involved in the nitrogen, sulfur, iron, and phosphate metabolism of MC-1, allowing us to infer the presence or absence of specific biochemical pathways in strain MC-1. The pathways inferred from the MC-1 genome provide important information regarding central metabolism in this strain that could provide insights useful for the isolation and cultivation of new magnetotactic bacterial strains, in particular strains of other magnetotactic cocci.

Production, Modification and Bio-Applications of Magnetic Nanoparticles Gestated by Magnetotactic Bacteria

Magnetotactic bacteria (MTB) were first discovered by Richard P. Blakemore in 1975, and this led to the discovery of a wide collection of microorganisms with similar features i.e., the ability to internalize Fe and convert it into magnetic nanoparticles, in the form of either magnetite (Fe(3)O(4)) or greigite (Fe(3)S(4)). Studies showed that these particles are highly crystalline, monodisperse, bioengineerable and have high magnetism that is comparable to those made by advanced synthetic methods, making them candidate materials for a broad range of bio-applications. In this review article, the history of the discovery of MTB and subsequent efforts to elucidate the mechanisms behind the magnetosome formation are briefly covered. The focus is on how to utilize the knowledge gained from fundamental studies to fabricate functional MTB nanoparticles (MTB-NPs) that are capable of tackling real biomedical problems.

Expression of green fluorescent protein fused to magnetosome proteins in microaerophilic magnetotactic bacteria

The magnetosomes of magnetotactic bacteria are prokaryotic organelles consisting of a magnetite crystal bounded by a phospholipid bilayer that contains a distinct set of proteins with various functions. Because of their unique magnetic and crystalline properties, magnetosome particles are potentially useful as magnetic nanoparticles in a number of applications, which in many cases requires the coupling of functional moieties to the magnetosome membrane. In this work, we studied the use of green fluorescent protein (GFP) as a reporter for the magnetosomal localization and expression of fusion proteins in the microaerophilic Magnetospirillum gryphiswaldense by flow cytometry, fluorescence microscopy, and biochemical analysis. Although optimum conditions for high fluorescence and magnetite synthesis were mutually exclusive, we established oxygen-limited growth conditions, which supported growth, magnetite biomineralization, and GFP fluorophore formation at reasonable rates. Under these optimized conditions, we studied the subcellular localization and expression of the GFP-tagged magnetosome proteins MamC, MamF, and MamG by fluorescence microscopy and immunoblotting. While all fusions specifically localized at the magnetosome membrane, MamC-GFP displayed the strongest expression and fluorescence. MamC-GFP-tagged magnetosomes purified from cells displayed strong fluorescence, which was sensitive to detergents but stable under a wide range of temperature and salt concentrations. In summary, our data demonstrate the use of GFP as a reporter for protein localization under magnetite-forming conditions and the utility of MamC as an anchor for magnetosome-specific display of heterologous gene fusions.