The ability of magnetotactic bacteria (MTB) to orient in magnetic fields is based on the synthesis of magnetosomes, which are unique prokaryotic organelles comprising membrane-enveloped, nano-sized ...crystals of a magnetic iron mineral that are aligned in well-ordered intracellular chains. Magnetosome crystals have species-specific morphologies, sizes, and arrangements. The magnetosome membrane, which originates from the cytoplasmic membrane by invagination, represents a distinct subcellular compartment and has a unique biochemical composition. The roughly 20 magnetosome-specific proteins have functions in vesicle formation, magnetosomal iron transport, and the control of crystallization and intracellular arrangement of magnetite particles. The assembly of magnetosome chains is under genetic control and involves the action of an acidic protein that links magnetosomes to a novel cytoskeletal structure, presumably formed by a specific actin-like protein. A total of 28 conserved genes present in various magnetic bacteria were identified to be specifically associated with the magnetotactic phenotype, most of which are located in the genomic magnetosome island. The unique properties of magnetosomes attracted broad interdisciplinary interest, and MTB have recently emerged as a model to study prokaryotic organelle formation and evolution.
Their unique material characteristics, i.e. high crystallinity, strong magnetization, uniform shape and size, and the ability to engineer the enveloping membrane in vivo make bacterial magnetosomes ...highly interesting for many biomedical and biotechnological applications. In this study, a versatile toolkit is developed for the multifunctionalization of magnetic nanoparticles in the magnetotactic bacterium Magnetospirillum gryphiswaldense, and the use of several abundant magnetosome membrane proteins as anchors for functional moieties is explored. High‐level magnetosome display of cargo proteins enables the generation of engineered nanoparticles with several genetically encoded functionalities, including a core–shell structure, magnetization, two different catalytic activities, fluorescence and the presence of a versatile connector that allows the incorporation into a hydrogel‐based matrix by specific coupling reactions. The resulting reusable magnetic composite demonstrates the high potential of synthetic biology for the production of multifunctional nanomaterials, turning the magnetosome surface into a platform for specific versatile display of functional moieties.
Using genetic engineering techniques, a versatile toolkit for the multifunctionalization of bacterial magnetic nanoparticles is developed. High‐level magnetosome display of different cargo proteins enables the generation of magnetic, fluorescent, catalytically active particles that can be efficiently incorporated into a hydrogel‐based matrix, which results in a multifunctional, reusable composite material.
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.
Summary
While magnetosome biosynthesis within the magnetotactic Proteobacteria is increasingly well understood, much less is known about the genetic control within deep‐branching phyla, which have a ...unique ultrastructure and biosynthesize up to several hundreds of bullet‐shaped magnetite magnetosomes arranged in multiple bundles of chains, but have no cultured representatives. Recent metagenomic analysis identified magnetosome genes in the genus ‘Candidatus Magnetobacterium’ homologous to those in Proteobacteria. However, metagenomic analysis has been limited to highly abundant members of the community, and therefore only little is known about the magnetosome biosynthesis, ecophysiology and metabolic capacity in deep‐branching MTB. Here we report the analysis of single‐cell derived draft genomes of three deep‐branching uncultivated MTB. Single‐cell sorting followed by whole genome amplification generated draft genomes of Candidatus Magnetobacterium bavaricum and Candidatus Magnetoovum chiemensis CS‐04 of the Nitrospirae phylum. Furthermore, we present the first, nearly complete draft genome of a magnetotactic representative from the candidate phylum Omnitrophica, tentatively named Candidatus Omnitrophus magneticus SKK‐01. Besides key metabolic features consistent with a common chemolithoautotrophic lifestyle, we identified numerous, partly novel genes most likely involved in magnetosome biosynthesis of bullet‐shaped magnetosomes and their arrangement in multiple bundles of chains.
Most motile bacteria navigate within gradients of external chemical stimuli by regulating the length of randomly oriented swimming episodes. Magnetotactic bacteria are characterized by chains of ...intracellular ferromagnetic nanoparticles and their ability to sense the geomagnetic field, which is believed to facilitate directed motion, but is not well understood at the behavioural and molecular level. Here, we show that cells of Magnetospirillum gryphiswaldense unexpectedly display swimming polarity that depends on aerotactic signal transduction through one of its four chemotaxis operons (cheOp1). Growth of cells in magnetic fields superimposed on oxygen gradients results in a gradual inherited bias of swimming runs with one of the cell poles leading, such that the resulting overall swimming direction of entire populations can be reversed by changes in oxygen concentration. These findings clearly show that there is a direct molecular link between aerotactic sensing and the determination of magnetotactic polarity, through the sensory pathway, CheOp1.
Magnetotactic bacteria are aquatic or sediment-dwelling microorganisms able to take advantage of the Earth's magnetic field for directed motility. The source of this amazing trait is magnetosomes, ...unique organelles used to synthesize single nanometer-sized crystals of magnetic iron minerals that are queued up to build an intracellular compass. Most of these microorganisms cannot be cultivated under controlled conditions, much less genetically engineered, with only few exceptions. However, two of the genetically amenable
species have emerged as tractable model organisms to study magnetosome formation and magnetotaxis. Recently, much has been revealed about the process of magnetosome biogenesis and dedicated structures for magnetosome dynamics and positioning, which suggest an unexpected cellular intricacy of these organisms. In this minireview, we summarize new insights and place the molecular mechanisms of magnetosome formation in the context of the complex cell biology of
spp. First, we provide an overview on magnetosome vesicle synthesis and magnetite biomineralization, followed by a discussion of the perceptions of dynamic organelle positioning and its biological implications, which highlight that magnetotactic bacteria have evolved sophisticated mechanisms to construct, incorporate, and inherit a unique navigational device. Finally, we discuss the impact of magnetotaxis on motility and its interconnection with chemotaxis, showing that magnetotactic bacteria are outstandingly adapted to lifestyle and habitat.
Magnetosomes are specialized organelles for magnetic navigation that comprise membrane-enveloped, nano-sized crystals of a magnetic iron mineral; they are formed by a diverse group of magnetotactic ...bacteria (MTB). The synthesis of magnetosomes involves strict genetic control over intracellular differentiation, biomineralization, and their assembly into highly ordered chains. Physicochemical control over biomineralization is achieved by compartmentalization within vesicles of the magnetosome membrane, which is a phospholipid bilayer associated with a specific set of proteins that have known or suspected functions in vesicle formation, iron transport, control of crystallization, and arrangement of magnetite particles. Magnetosome formation is genetically complex, and relevant genes are predominantly located in several operons within a conserved genomic magnetosome island that has been likely transferred horizontally and subsequently adapted between diverse MTB during evolution. This review summarizes the recent progress in our understanding of magnetobacterial cell biology, genomics, and the genetic control of magnetosome formation and magnetotaxis.
Bacterial magnetosomes are membrane-enveloped, nanometer-sized crystals of magnetite, which serve for magnetotactic navigation. All genes implicated in the synthesis of these organelles are located ...in a conserved genomic magnetosome island (MAI). We performed a comprehensive bioinformatic, proteomic and genetic analysis of the MAI in Magnetospirillum gryphiswaldense. By the construction of large deletion mutants we demonstrate that the entire region is dispensable for growth, and the majority of MAI genes have no detectable function in magnetosome formation and could be eliminated without any effect. Only <25% of the region comprising four major operons could be associated with magnetite biomineralization, which correlated with high expression of these genes and their conservation among magnetotactic bacteria. Whereas only deletion of the mamAB operon resulted in the complete loss of magnetic particles, deletion of the conserved mms6, mamGFDC, and mamXY operons led to severe defects in morphology, size and organization of magnetite crystals. However, strains in which these operons were eliminated together retained the ability to synthesize small irregular crystallites, and weakly aligned in magnetic fields. This demonstrates that whereas the mamGFDC, mms6 and mamXY operons have crucial and partially overlapping functions for the formation of functional magnetosomes, the mamAB operon is the only region of the MAI, which is necessary and sufficient for magnetite biomineralization. Our data further reduce the known minimal gene set required for magnetosome formation and will be useful for future genome engineering approaches.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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