Magnetosome Biomineralization Research Articles

Complete Genome Sequence of Strain BW-2, a Magnetotactic Gammaproteobacterium in the Family Ectothiorhodospiraceae, Isolated from a Brackish Spring in Death Valley, California.

We report the complete 4.1-Mb genome sequence of strain BW-2, a magnetotactic, sulfur-oxidizing rod, belonging to the family Ectothiorhodospiraceae of the class Gammaproteobacteria, that biomineralizes membrane-bounded magnetite nanocrystals in its magnetosomes. This genome sequence, in comparison with those of other magnetotactic bacteria, is essential for understanding the origin and evolution of magnetotaxis and magnetosome biomineralization.

Genome-Based Metabolic Reconstruction of a Novel Uncultivated Freshwater Magnetotactic coccus "Ca. Magnetaquicoccus inordinatus" UR-1, and Proposal of a Candidate Family "Ca. Magnetaquicoccaceae".

Magnetotactic bacteria are widely represented microorganisms that have the ability to synthesize magnetosomes. The magnetotactic cocci of the order Magnetococcales are the most frequently identified, but their classification remains unclear due to the low number of cultivated representatives. This paper reports the analysis of an uncultivated magnetotactic coccus UR-1 collected from the Uda River (in eastern Siberia). Genome analyses of this bacterium and comparison to the available Magnetococcales genomes identified a novel species called “Ca. Magnetaquicoccus inordinatus,” and a delineated candidate family “Ca. Magnetaquicoccaceae” within the order Magnetococcales is proposed. We used average amino acid identity values <55–56% and <64–65% as thresholds for the separation of families and genera, respectively, within the order Magnetococcales. Analyses of the genome sequence of UR-1 revealed a potential ability for a chemolithoautotrophic lifestyle, with the oxidation of a reduced sulfur compound and carbon assimilation by rTCA. A nearly complete magnetosome genome island, containing a set of mam and mms genes, was also identified. Further comparative analyses of the magnetosome genes showed vertical inheritance as well as horizontal gene transfer as the evolutionary drivers of magnetosome biomineralization genes in strains of the order Magnetococcales.

Epsilon-Fe2O3 is a novel intermediate for magnetite biosynthesis in magnetotactic bacteria

BackgroundNatural biological magnetite nanoparticles are widely distributed from microorganisms to humans. It is found to be very important in organisms, especially in navigation. Moreover, purified magnetite nanoparticles also have potential applications in bioengineering and biomedicine. Magnetotactic bacteria (MTB) is considered one of the most abundant species around the world which can form intracellular membrane enveloped magnetic nanoparticles, referred to as magnetosomes. To our knowledge, the biomineralization of magnetosome in MTB involves a serious of genes located on a large unstable genomic region named magnetosome island, which specially exists in MTB. The magnetite core of magnetosome formed via a Fe (III) ion intermediates, for instance, α-Fe2O3 and ferrihydrite. Though the biosynthesis of magnetosome represents a general biomineralization mechanism of biogenic magnetite, knowledge of magnetosome biosynthesis and biomineralization remains very limited.MethodCells used in this study were cultured in a 7.5-L bioreactor, samples for intermediate capture were taken each certain time interval after the generation of magnetosome biosynthesis condition. High-resolution transmission electron microscopy were used to analyze the detailed structure of magnetosomes. The parameters of the crystal structures were obtained by Fast Fourier Transform analyses.ResultsIn this study, we identified a novel intermediate phase, ε-Fe2O3, during the magnetite maturation process in MTB via kinetic analysis. Unlike α-Fe2O3, which has been reported as a precursor during magnetosome biosynthesis in MTB before, ε-Fe2O3, due to its thermal instability, is a rare phase with scarce natural abundance. This finding confirmed that ε-Fe2O3 is an important novel intermediate during the biomineralization of magnetosome in MTB, and shed new light on the magnetosome biosynthesis pathway.

Tuning properties of biomimetic magnetic nanoparticles by combining magnetosome associated proteins

The role of magnetosome associated proteins on the in vitro synthesis of magnetite nanoparticles has gained interest, both to obtain a better understanding of the magnetosome biomineralization process and to be able to produce novel magnetosome-like biomimetic nanoparticles. Up to now, only one recombinant protein has been used at the time to in vitro form biomimetic magnetite precipitates, being that a scenario far enough from what probably occurs in the magnetosome. In the present study, both Mms6 and MamC from Magnetococcus marinus MC-1 have been used to in vitro form biomimetic magnetites. Our results show that MamC and Mms6 have different, but complementary, effects on in vitro magnetite nucleation and growth. MamC seems to control the kinetics of magnetite nucleation while Mms6 seems to preferably control the kinetics for crystal growth. Our results from the present study also indicate that it is possible to combine both proteins to tune the properties of the resulting biomimetic magnetites. In particular, by changing the relative ratio of these proteins, better faceted and/or larger magnetite crystals with, consequently, different magnetic moment per particle could be obtained. This study provides with tools to obtain new biomimetic nanoparticles with a potential utility for biotechnological applications.

Magnetosomes: biogenic iron nanoparticles produced by environmental bacteria.

The scientific community's interest in magnetotactic bacteria has increased substantially in recent decades. These prokaryotes have the particularity of synthesizing nanomagnets, called magnetosomes. The majority of research is based on several scientific questions. Where do magnetotactic bacteria live, what are their characteristics, and why are they magnetic? What are the molecular phenomena of magnetosome biomineralization and what are the physical characteristics of magnetosomes? In addition to scientific curiosity to better understand these stunning organisms, there are biotechnological opportunities to consider. Magnetotactic bacteria, as well as magnetosomes, are used in medical applications, for example cancer treatment, or in environmental ones, for example bioremediation. In this mini-review, we investigated all the aspects mentioned above and summarized the currently available knowledge.

Investigation of the magnetosome biomineralization in magnetotactic bacteria using graphene liquid cell - transmission electron microscopy.

Understanding the biomineralization pathways in living biological species is a grand challenge owing to the difficulties in monitoring the mineralization process at sub-nanometer scales. Here, we monitored the nucleation and growth of magnetosome nanoparticles in bacteria and in real time using a transmission electron microscope (TEM). To enable biomineralization within the bacteria, we subcultured magnetotactic bacteria grown in iron-depleted medium and then mixed them with iron-rich medium within graphene liquid cells (GLCs) right before imaging the bacteria under the microscope. Using in situ electron energy loss spectroscopy (EELS), the oxidation state of iron in the biomineralized magnetosome was analysed to be magnetite with trace amount of hematite. The increase of mass density of biomineralized magnetosomes as a function of incubation time indicated that the bacteria maintained their functionality during the in situ TEM imaging. Our results underpin that GLCs enables a new platform to observe biomineralization events in living biological species at unprecedented spatial resolution. Understanding the biomineralization processes in living organisms facilitates the design of biomimetic materials, and will enable a paradigm shift in understanding the evolution of biological species.

Magnetotactic Coccus Strain SHHC-1 Affiliated to Alphaproteobacteria Forms Octahedral Magnetite Magnetosomes.

Magnetotactic bacteria (MTB) are morphologically and phylogenetically diverse prokaryotes. They can form intracellular chain-assembled magnetite (Fe3O4) or greigite (Fe3S4) nanocrystals each enveloped by a lipid bilayer membrane called a magnetosome. Magnetotactic cocci have been found to be the most abundant morphotypes of MTB in various aquatic environments. However, knowledge on magnetosome biomineralization within magnetotactic cocci remains elusive due to small number of strains that have been cultured. By using a coordinated fluorescence and scanning electron microscopy method, we discovered a unique magnetotactic coccus strain (tentatively named SHHC-1) in brackish sediments collected from the estuary of Shihe River in Qinhuangdao city, eastern China. It phylogenetically belongs to the Alphaproteobacteria class. Transmission electron microscopy analyses reveal that SHHC-1 cells formed many magnetite-type magnetosomes organized as two bundles in each cell. Each bundle contains two parallel chains with smaller magnetosomes generally located at the ends of each chain. Unlike most magnetotactic alphaproteobacteria that generally form magnetosomes with uniform crystal morphologies, SHHC-1 magnetosomes display a more diverse variety of crystal morphology even within a single cell. Most particles have rectangular and rhomboidal projections, whilst others are triangular, or irregular. High resolution transmission electron microscopy observations coupled with morphological modeling indicate an idealized model—elongated octahedral crystals, a form composed of eight {111} faces. Furthermore, twins, multiple twins and stack dislocations are frequently observed in the SHHC-1 magnetosomes. This suggests that biomineralization of strain SHHC-1 magnetosome might be less biologically controlled than other magnetotactic alphaproteobacteria. Alternatively, SHHC-1 is more sensitive to the unfavorable environments under which it lives, or a combination of both factors may have controlled the magnetosome biomineralization process within this unique MTB.

The Disruption of an OxyR-Like Protein Impairs Intracellular Magnetite Biomineralization in Magnetospirillum gryphiswaldense MSR-1.

Magnetotactic bacteria synthesize intracellular membrane-enveloped magnetite bodies known as magnetosomes which have been applied in biotechnology and medicine. A series of proteins involved in ferric ion transport and redox required for magnetite formation have been identified but the knowledge of magnetosome biomineralization remains very limited. Here, we identify a novel OxyR homolog (named OxyR-Like), the disruption of which resulted in low ferromagnetism and disfigured nano-sized iron oxide crystals. High resolution-transmission electron microscopy showed that these nanoparticles are mainly composed of magnetite accompanied with ferric oxide including α-Fe2O3 and 𝜀-Fe2O3. Electrophoretic mobility shift assay and DNase I footprinting showed that OxyR-Like binds the conserved 5′-GATA-N{9}-TATC-3′ region within the promoter of pyruvate dehydrogenase (pdh) complex operon. Quantitative real-time reverse transcriptase PCR indicated that not only the expression of pdh operon but also genes related to magnetosomes biosynthesis and tricarboxylic acid cycle decreased dramatically, suggesting a link between carbon metabolism and magnetosome formation. Taken together, our results show that OxyR-Like plays a key role in magnetosomes formation.

Measuring spectroscopy and magnetism of extracted and intracellular magnetosomes using soft X-ray ptychography

Characterizing the chemistry and magnetism of magnetotactic bacteria (MTB) is an important aspect of understanding the biomineralization mechanism and function of the chains of magnetosomes (Fe3O4 nanoparticles) found in such species. Images and X-ray absorption spectra (XAS) of magnetosomes extracted from, and magnetosomes in, whole Magnetovibrio blakemorei strain MV-1 cells have been recorded using soft X-ray ptychography at the Fe 2p edge. A spatial resolution of 7 nm is demonstrated. Precursor-like and immature magnetosome phases in a whole MV-1 cell were visualized, and their Fe 2p spectra were measured. Based on these results, a model for the pathway of magnetosome biomineralization for MV-1 is proposed. Fe 2p X-ray magnetic circular dichroism (XMCD) spectra have been derived from ptychography image sequences recorded using left and right circular polarization. The shape of the XAS and XMCD signals in the ptychographic absorption spectra of both sample types is identical to the shape and signals measured with conventional bright-field scanning transmission X-ray microscope. A weaker and inverted XMCD signal was observed in the ptychographic phase spectra of the extracted magnetosomes. The XMCD ptychographic phase spectrum of the intracellular magnetosomes differed from the ptychographic phase spectrum of the extracted magnetosomes. These results demonstrate that spectro-ptychography offers a superior means of characterizing the chemical and magnetic properties of MTB at the individual magnetosome level.

Diversity of &lt;i&gt;Magnetospirillum&lt;/i&gt; Sp. from the Southern Coast of India

Magnetotactic bacteria (MTB) are ubiquitous in the aquatic environment and have been identified from almost every continent; however, there are only a few reports of MTB from India. This article studies the diversity of cultivable MTB from the southern coast of India. Five strains of MTB have been identified in this study using gradient culturing; three of the five strains were isolated in pure culture. The strains iden-tified are vibrioid to helical in morphology and grow microaerophilically in oxygen-sulphide gradient me-dia. Phylogenetic analysis of isolates based on 16S rRNA gene sequences shows that they belong to the family Rhodospirillaceae, class Alphaproteobacteria, and genus Magnetospirillum . The three isolated strains were physiologically characterized and found to utilize a wide range of substrates as electron donors and electron acceptors for metabolism. The autotrophic growth of the strains was confirmed by the detection of type-II RuBisCO ( cbb M) gene by PCR amplifi-cation. The presence of key magnetosome formation ( mam ) genes in the strains confirms the similar mechanism of magnetosome biomineralization among Magnetospirillum species. These reports of MTB from the Indian coast would contribute to the study of their evolution and biomineralization.

Genetic and Ultrastructural Analysis Reveals the Key Players and Initial Steps of Bacterial Magnetosome Membrane Biogenesis.

Magnetosomes of magnetotactic bacteria contain well-ordered nanocrystals for magnetic navigation and have recently emerged as the most sophisticated model system to study the formation of membrane bounded organelles in prokaryotes. Magnetosome biosynthesis is thought to begin with the formation of a dedicated compartment, the magnetosome membrane (MM), in which the biosynthesis of a magnetic mineral is strictly controlled. While the biomineralization of magnetosomes and their subsequent assembly into linear chains recently have become increasingly well studied, the molecular mechanisms and early stages involved in MM formation remained poorly understood. In the Alphaproteobacterium Magnetospirillum gryphiswaldense, approximately 30 genes were found to control magnetosome biosynthesis. By cryo-electron tomography of several key mutant strains we identified the gene complement controlling MM formation in this model organism. Whereas the putative magnetosomal iron transporter MamB was most crucial for the process and caused the most severe MM phenotype upon elimination, MamM, MamQ and MamL were also required for the formation of wild-type-like MMs. A subset of seven genes (mamLQBIEMO) combined within a synthetic operon was sufficient to restore the formation of intracellular membranes in the absence of other genes from the key mamAB operon. Tracking of de novo magnetosome membrane formation by genetic induction revealed that magnetosomes originate from unspecific cytoplasmic membrane locations before alignment into coherent chains. Our results indicate that no single factor alone is essential for MM formation, which instead is orchestrated by the cumulative action of several magnetosome proteins.

Repairing human tooth enamel with leucine-rich amelogenin peptide-chitosan hydrogel - Erratum Following iron speciation in the early stages of magnetite magnetosome biomineralization - Erratum

Mukherjee et al.11 and Firlar et al.2 were improperly categorized as Reviews in their recent publications. They are both intended to be Biomineralization and Biomimetics Articles.

A novel role for Crp in controlling magnetosome biosynthesis in Magnetospirillum gryphiswaldense MSR-1

Magnetotactic bacteria (MTB) are specialized microorganisms that synthesize intracellular magnetite particles called magnetosomes. Although many studies have focused on the mechanism of magnetosome synthesis, it remains unclear how these structures are formed. Recent reports have suggested that magnetosome formation is energy dependent. To investigate the relationship between magnetosome formation and energy metabolism, a global regulator, named Crp, which mainly controls energy and carbon metabolism in most microorganisms, was genetically disrupted in Magnetospirillum gryphiswaldense MSR-1. Compared with the wild-type or complemented strains, the growth, ferromagnetism and intracellular iron content of crp-deficient mutant cells were dramatically decreased. Transmission electron microscopy (TEM) showed that magnetosome synthesis was strongly impaired by the disruption of crp. Further gene expression profile analysis showed that the disruption of crp not only influenced genes related to energy and carbon metabolism, but a series of crucial magnetosome island (MAI) genes were also down regulated. These results indicate that Crp is essential for magnetosome formation in MSR-1. This is the first time to demonstrate that Crp plays an important role in controlling magnetosome biomineralization and provides reliable expression profile data that elucidate the mechanism of Crp regulation of magnetosome formation in MSR-1.

Characterizing and optimizing magnetosome production of Magnetospirillum sp. XM-1 isolated from Xi'an City Moat, China.

Pure culture of magnetotactic bacteria is desirable to understand their physiology, evolution and biomineralization. Here, we report a new strain Magnetospirillum sp. XM-1 that was recently isolated and cultivated from the eutrophic city moat of Xi'an, China. Magnetosome biomineralization, crystallographic and magnetic properties of XM-1 were characterized by using a combination of transmission electron microscopy and rock magnetic methods. Cell growth and magnetite production was optimized by response surface methodology. We found that the Magnetospirillum strain XM-1 is different from the model strain Magnetospirillum magneticum AMB-1 in terms of magnetite magnetosomes, optimal growth temperature and nutrient requirements. Sodium succinate, sodium nitrate and ferric citrate are the three most significant factors associated with the optimization of cell growth and magnetosome production for XM-1.

Size control of in vitro synthesized magnetite crystals by the MamC protein of Magnetococcus marinus strain MC-1.

Magnetotactic bacteria are a diverse group of prokaryotes that share the unique ability of biomineralizing magnetosomes, which are intracellular, membrane-bounded crystals of either magnetite (Fe3O4) or greigite (Fe3S4). Magnetosome biomineralization is mediated by a number of specific proteins, many of which are localized in the magnetosome membrane, and thus is under strict genetic control. Several studies have partially elucidated the effects of a number of these magnetosome-associated proteins in the control of the size of magnetosome magnetite crystals. However, the effect of MamC, one of the most abundant proteins in the magnetosome membrane, remains unclear. In this present study, magnetite nanoparticles were synthesized inorganically in free-drift experiments at 25 °C in the presence of different concentrations of the iron-binding recombinant proteins MamC and MamCnts (MamC without its first transmembrane segment) from the marine, magnetotactic bacterium Magnetococcus marinus strain MC-1 and three commercial proteins [α-lactalbumin (α-Lac), myoglobin (Myo), and lysozyme (Lyz)]. While no effect was observed on the size of magnetite crystals formed in the presence of the commercial proteins, biomimetic synthesis in the presence of MamC and MamCnts at concentrations of 10-60 μg/mL resulted in the production of larger and more well-developed magnetite crystals (~30-40 nm) compared to those of the control (~20-30 nm; magnetite crystals grown protein-free). Our results demonstrate that MamC plays an important role in the control of the size of magnetite crystals and could be utilized in biomimetic synthesis of magnetite nanocrystals.

A putative greigite-type magnetosome gene cluster from the candidate phylum Latescibacteria.

The intracellular biomineralization of magnetite and/or greigite magnetosomes in magnetotactic bacteria (MTB) is strictly controlled by a group of conserved genes, termed magnetosome genes, which are organized as clusters (or islands) in MTB genomes. So far, all reported MTB are affiliated within the Proteobacteria phylum, the Nitrospirae phylum and the candidate division OP3. Here, we report the discovery of a putative magnetosome gene cluster structure from the draft genome of an uncultivated bacterium belonging to the candidate phylum Latescibacteria (formerly candidate division WS3) recently recovered by Rinke and colleagues, which contains 10 genes with homology to magnetosome mam genes of magnetotactic Proteobacteria and Nitrospirae. Moreover, these genes are phylogenetically closely related to greigite-type magnetosome genes that were only found from the Deltaproteobacteria MTB before, suggesting that the greigite genes may originate earlier than previously imagined. These findings indicate that some members of Latescibacteria may be capable of forming greigite magnetosomes, and thus may play previously unrecognized roles in environmental iron and sulfur cycles. The conserved genomic structure of magnetosome gene cluster in Latescibacteria phylum supports the hypothesis of horizontal transfer of these genes among distantly related bacterial groups in nature.

Properties of magnetite nanoparticles produced by magnetotactic bacteria

The magnetic nanoparticles (magnetite) were prepared through the fermentation of the Magnetospirillum strain WM-1 newly isolated by our group. The samples were characterized by TEM, SAED, XRD, rock magnetic analysis, and Mossbauer spectroscopy. TEM and SAED measurements showed that the magnetosomes formed by strain WM-1 were single crystallites of high perfection with a cubic spinel structure of magnetite. X-ray measurements also fitted very well with standard Fe3O4 reflections with an inverse spinel structure of the magnetite core. The size of crystal as calculated by the Debye-Scherrer’s equation was approximately 55 nm. Rock magnetic analysis showed WM-1 synthesized single-domain magnetite magnetosomes, which were arranged in the form of linear chain. The high delta ratio ((δFC / δZFC = 4) supported the criteria of Moskowitz test that there were intact magnetosomes chains in cells. The Verwey transition occurred at 105 K that closed to stoochiometric magnetite in composition. These observations provided useful insights into the biomineralization of magnetosomes and properties of M. WM-1 and potential application of biogenic magnetite in biomaterials and biomagnetism.

Bacterial magnetosome biomineralization--a novel platform to study molecular mechanisms of human CDF-related Type-II diabetes.

Cation diffusion facilitators (CDF) are part of a highly conserved protein family that maintains cellular divalent cation homeostasis in all organisms. CDFs were found to be involved in numerous human health conditions, such as Type-II diabetes and neurodegenerative diseases. In this work, we established the magnetite biomineralizing alphaproteobacterium Magnetospirillum gryphiswaldense as an effective model system to study CDF-related Type-II diabetes. Here, we introduced two ZnT-8 Type-II diabetes-related mutations into the M. gryphiswaldense MamM protein, a magnetosome-associated CDF transporter essential for magnetite biomineralization within magnetosome vesicles. The mutations' effects on magnetite biomineralization and iron transport within magnetosome vesicles were tested in vivo. Additionally, by combining several in vitro and in silico methodologies we provide new mechanistic insights for ZnT-8 polymorphism at position 325, located at a crucial dimerization site important for CDF regulation and activation. Overall, by following differentiated, easily measurable, magnetism-related phenotypes we can utilize magnetotactic bacteria for future research of CDF-related human diseases.

Genetic dissection of the mamAB and mms6 operons reveals a gene set essential for magnetosome biogenesis in Magnetospirillum gryphiswaldense.

Biosynthesis of bacterial magnetosomes, which are intracellular membrane-enclosed, nanosized magnetic crystals, is controlled by a set of >30 specific genes. In Magnetospirillum gryphiswaldense, these are clustered mostly within a large conserved genomic magnetosome island (MAI) comprising the mms6, mamGFDC, mamAB, and mamXY operons. Here, we demonstrate that the five previously uncharacterized genes of the mms6 operon have crucial functions in the regulation of magnetosome biomineralization that partially overlap MamF and other proteins encoded by the adjacent mamGFDC operon. While all other deletions resulted in size reduction, elimination of either mms36 or mms48 caused the synthesis of magnetite crystals larger than those in the wild type (WT). Whereas the mms6 operon encodes accessory factors for crystal maturation, the large mamAB operon contains several essential and nonessential genes involved in various other steps of magnetosome biosynthesis, as shown by single deletions of all mamAB genes. While single deletions of mamL, -P, -Q, -R, -B, -S, -T, and -U showed phenotypes similar to those of their orthologs in a previous study in the related M. magneticum, we found mamI and mamN to be not required for at least rudimentary iron biomineralization in M. gryphiswaldense. Thus, only mamE, -L, -M, -O, -Q, and -B were essential for formation of magnetite, whereas a mamI mutant still biomineralized tiny particles which, however, consisted of the nonmagnetic iron oxide hematite, as shown by high-resolution transmission electron microscopy (HRTEM) and the X-ray absorption near-edge structure (XANES). Based on this and previous studies, we propose an extended model for magnetosome biosynthesis in M. gryphiswaldense.

Subcellular localization of the magnetosome protein MamC in the marine magnetotactic bacterium Magnetococcus marinus strain MC-1 using immunoelectron microscopy.

Magnetotactic bacteria are a diverse group of prokaryotes that biomineralize intracellular magnetosomes, composed of magnetic (Fe3O4) crystals each enveloped by a lipid bilayer membrane that contains proteins not found in other parts of the cell. Although partial roles of some of these magnetosome proteins have been determined, the roles of most have not been completely elucidated, particularly in how they regulate the biomineralization process. While studies on the localization of these proteins have been focused solely on Magnetospirillum species, the goal of the present study was to determine, for the first time, the localization of the most abundant putative magnetosome membrane protein, MamC, in Magnetococcus marinus strain MC-1. MamC was expressed in Escherichia coli and purified. Monoclonal antibodies were produced against MamC and immunogold labeling TEM was used to localize MamC in thin sections of cells of M. marinus. Results show that MamC is located only in the magnetosome membrane of Mc. marinus. Based on our findings and the abundance of this protein, it seems likely that it is important in magnetosome biomineralization and might be used in controlling the characteristics of synthetic nanomagnetite.