Magnetotactic Bacteria Research Articles

Magnetochrome-catalyzed oxidation of ferrous iron by MamP enables magnetite crystal growth in the magnetotactic bacterium AMB-1

Magnetotactic bacteria have evolved the remarkable capacity to biomineralize chains of magnetite [Fe(II)Fe(III)2O4] nanoparticles that align along the geomagnetic field and optimize their navigation in the environment. Mechanisms enabling magnetite formation require the complex action of numerous proteins for iron acquisition, sequestration in dedicated magnetosome organelles, and precipitation into magnetite. The MamP protein contains c-type cytochromes called magnetochrome domains that are found exclusively in magnetotactic bacteria. Ablation of magnetochromes in MamP prevents bacteria from aligning with external magnetic fields, showing their importance to maintain this biological function. MamP has been proposed, mostly from in vitro experimentations, to regulate iron redox state and maintain an Fe(II)/Fe(III) balance compatible with magnetite formation via the iron oxidase activity of magnetochromes. To test the proposed function for MamP in vivo in the magnetotactic strain Magnetospirillum magneticum (AMB)-1, we characterized the iron species in chemical MamP-mediated magnetite syntheses as well as in bacteria unable to produce MamP using a combination of physicochemical methodologies. We show that MamP has no apparent control on the speciation and oxidation state of intracellular iron or on the Fe(II)/Fe(III) balance in magnetite. We propose that MamP promotes magnetite growth by incorporating Fe(III) into preexisting magnetite seeds and that magnetite structure and stoichiometry is maintained by further equilibration with dissolved Fe(II) in magnetosome organelles.

Heating Efficiency of Different Magnetotactic Bacterial Species: Influence of Magnetosome Morphology and Chain Arrangement.

Magnetotactic bacteria have been proposed as ideal biological nanorobots due to the presence of an intracellular chain of magnetic nanoparticles (MNPs), which allows them to be guided and controlled by external magnetic fields and provides them with theragnostic capabilities intrinsic to magnetic nanoparticles, such as magnetic hyperthermia for cancer treatment. Here, we study three different bacterial species, Magnetospirillum gryphiswaldense (MSR-1), Magnetospirillum magneticum (AMB-1), and Magnetovibrio blakemorei (MV-1), which synthesize magnetite nanoparticles with different morphologies and chain arrangements. We analyzed the impact of these parameters on the effective magnetic anisotropy, Keff, and the heating capacity or Specific Absorption Rate, SAR, under alternating magnetic fields. SAR values have been obtained from the area of experimental AC hysteresis loops, while Keff has been determined from simulations of AC hysteresis loops using a dynamic Stoner-Wohlfarth model. The results demonstrate a clear relationship between the effective magnetic anisotropy and the heating efficiency of bacteria. As the Keff value increases, the saturated SAR values are higher; however, the threshold magnetic field required to observe a SAR response simultaneously increases. This factor is crucial to choose a bacterial species as the optimal hyperthermia agent.

Combined response of polar magnetotaxis to oxygen and pH: Insights from hanging drop assays and microcosm experiments

Magnetotactic bacteria (MTB) combine passive alignment with the Earth magnetic field with a chemotactic response (magneto-chemotaxis) to reach their optimal living depth in chemically stratified environments. Current magneto-aerotaxis models fail to explain the occurrence of MTB far below the oxic-anoxic interface and the coexistence of MTB cells with opposite magnetotactic polarity at depths that are unrelated with the redox gradient. Here we propose a modified model of polar magnetotaxis which explains these observations, as well as the distinct concentration profiles and magnetotactic advantages of two types of MTB inhabiting a freshwater sediment: a group of unidentified cocci (MC), and a giant rod-shaped bacterium (MB) apparently identical to M. bavaricum (MB). This model assumed that magnetotactic polarity is set by a threshold mechanism in counter gradients of oxygen and a second group of repellents, with, in case of MB, includes H+ ions. MTB possessing this type of polar magnetotaxis can shuttle between two limit depths across the redox gradient (redox taxis), as previously postulated for M. bavaricum and other members of the Nitrospirota group. The magnetotaxis of MB and MC is predominantly dipolar whenever the presence of a magnetic field ensures a magnetotactic advantage. In addition, MB can overcome unfavorable magnetic field configurations through a temporal sensing mechanism. The availability of threshold and temporal sensing mechanisms of different substances can generate a rich variety of responses by different types of MTB, enabling them to exploit multiple ecological niches.

Essential magnetosome proteins MamI and MamL from magnetotactic bacteria interact in mammalian cells

To detect cellular activities deep within the body using magnetic resonance platforms, magnetosomes are the ideal model of genetically-encoded nanoparticles. These membrane-bound iron biominerals produced by magnetotactic bacteria are highly regulated by approximately 30 genes; however, the number of magnetosome genes that are essential and/or constitute the root structure upon which biominerals form is largely undefined. To examine the possibility that key magnetosome genes may interact in a foreign environment, we expressed mamI and mamL as fluorescent fusion proteins in mammalian cells. Localization and potential protein-protein interaction(s) were investigated using confocal microscopy and fluorescence correlation spectroscopy (FCS). Enhanced green fluorescent protein (EGFP)-MamI and the red fluorescent Tomato-MamL displayed distinct intracellular localization, with net-like and punctate fluorescence, respectively. Remarkably, co-expression revealed co-localization of both fluorescent fusion proteins in the same punctate pattern. An interaction between MamI and MamL was confirmed by co-immunoprecipitation. In addition, changes in EGFP-MamI distribution were accompanied by acquisition of intracellular mobility which all Tomato-MamL structures displayed. Analysis of extracts from these cells by FCS was consistent with an interaction between fluorescent fusion proteins, including an increase in particle radius. Co-localization and interaction of MamI and MamL demonstrate that select magnetosome proteins may associate in mammalian cells.

An Integrated Approach to Elucidate the Interplay between Iron Uptake Dynamics and Magnetosome Formation at the Single-Cell Level in Magnetospirillum gryphiswaldense.

Iron is a crucial element integral to various fundamental biological molecular mechanisms, including magnetosome biogenesis in magnetotactic bacteria (MTB). Magnetosomes are formed through the internalization and biomineralization of iron into magnetite crystals. However, the interconnected mechanisms by which MTB uptake and regulate intracellular iron for magnetosome biomineralization remain poorly understood, particularly at the single-cell level. To gain insights we employed a holistic multiscale approach, i.e., from elemental iron species to bacterial populations, to elucidate the interplay between iron uptake dynamics and magnetosome formation in Magnetospirillum gryphiswaldense MSR-1 under near-native conditions. We combined a correlative microscopy approach integrating light and X-ray tomography with analytical techniques, such as flow cytometry and inductively coupled plasma spectroscopy, to evaluate the effects of iron and oxygen availability on cellular growth, magnetosome biogenesis, and intracellular iron pool in MSR-1. Our results revealed that increased iron availability under microaerobic conditions significantly promoted the formation of longer magnetosome chains and increased intracellular iron uptake, with a saturation point at 300 μM iron citrate. Beyond this threshold, additional iron did not further extend the magnetosome chain length or increase total intracellular iron levels. Moreover, our work reveals (i) a direct correlation between the labile Fe2+ pool size and magnetosome content, with higher intracellular iron concentrations correlating with increased magnetosome production, and (ii) the existence of an intracellular iron pool, distinct from magnetite, persisting during all stages of biomineralization. This study offers insights into iron dynamics in magnetosome biomineralization at a single-cell level, potentially enhancing the industrial biomanufacturing of magnetosomes.

Magnetosomes as Potential Nanocarriers for Cancer Treatment.

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

The Origin of Magnetofossil Coercivity Components: Constraints From Coupled Experimental Observations and Micromagnetic Calculations

AbstractBiogenic magnetite crystals produced by magnetotactic bacteria (MTB) and associated magnetofossils in sediments are characterized by variable morphologies, grain sizes, and chain structures. Magnetofossils are widely used in paleomagnetic and paleoenvironmental studies, but the complex magnetofossil shapes and particle arrangements significantly affect magnetic properties, hampering their magnetic detection and proxy interpretation. Here we perform coupled experimental and micromagnetic modeling analyses of typical magnetofossil‐rich sediments, where the effects of magnetofossil crystal forms and microstructures on magnetic properties can be quantitatively separated. Since the in situ magnetofossil chain structures in sediments remain poorly known, we compare results from magnetic measurements and micromagnetic simulations based on realistic magnetofossil shapes and grain size distributions. Our results suggest that bullet‐shaped magnetofossils certainly contribute to the biogenic hard (BH) coercivity component with a minor contribution from elongated prismatic particles, and collapsed equidimensional grains to the biogenic soft (BS) component. Micromagnetic simulations with different collapse models of bullet‐shaped magnetofossils produce variable FORC (first‐order reversal curve) central‐ridge contributions with similar coercivity distributions. Sensitivity test suggests that samples containing different forms of magnetofossils can produce the BH coercivity component if the proportion of the bullet‐shaped particles is more than ∼2%. Magnetofossil assemblages with a higher proportion of bullet‐shaped particles have higher coercivities, squareness ratios, and larger BH contents. Our data shed new light on understanding the origin of magnetofossil coercivity components and the in situ magnetofossil microstructures in sediments, which is widely useful for interpreting magnetofossil proxy signals in geological records.

Escape motility of multicellular magnetotactic prokaryotes.

Microorganisms often actively respond to multiple external stimuli to navigate toward their preferred niches. For example, unicellular magnetotactic bacteria integrate both oxygen sensory information and the Earth's geomagnetic field to help them locate anoxic conditions in a process known as magneto-aerotaxis. However, for multicellular magnetotactic prokaryotes (MMPs), the colonial structure of 4-16 cells places fundamental constraints on collective sensing, colony motility and directed swimming. To investigate how colonies navigate environments with multiple stimuli, we performed microfluidic experiments of MMPs with opposing magnetic fields and oxygen gradients. These experiments reveal unusual back-and-forth excursions called 'escape motility', in which colonies shuttle along magnetic field lines, punctuated by abrupt-yet highly coordinated-changes in collective ciliary beating. Through cell tracking and numerical simulations, we demonstrate that escape motility can arise through a simple magneto-aerotaxis mechanism, which includes the effect of magnetic torques and chemical sensing. At sufficiently high densities of MMPs, we observe the formation of dynamic crystal structures, whose stability is governed by the magnetic field strength and near-field hydrodynamic interactions. The results shed light on how some of the earliest multicellular organisms navigate complex physico-chemical landscapes.

Magnetotactic bacteria and magnetosomes – an overview

Magnetotactic bacteria are a diverse group of prokaryotes that create intracellular, membrane-bound organelles containing magnetic minerals known as magnetosomes. These minerals have a sdpecialized purpose with the use of mineral crystals such as magnetite (Fe3O4) or greigite (Fe3S4). Due to the stability of these crystal structures, the bacteria can orient themselves with the Earth’s geomagnetic field lines, functioning as compass needles to help them locate suitable environments to inhabit. The objective of this review, based on previous progressions in this area of study, is focused on presenting a comprehensive summary of MTB, its abundance and magnetosome formation. Moreover, the effects of certain environmental factors, as well as their significance and applications in material science, medicine, and biotechnology, are elucidated.

Sedimentary Greigite Formation

Revised thermodynamic data for greigite (Fe3S4) indicate that it is a stable sedimentary Fe-S phase. Greigite was previously regarded as metastable. Equilibrium computations using revised data explain apparently contradictory observations regarding greigite occurrences in sediments and sedimentary rocks. Greigite has a large stability area in pe-pH space relative to pyrite. It dominates in low pe regimes especially near the lower water stability boundary, which is consistent with its widespread occurrence in methanic sediments. It also has a small but significant stability zone near the sulfate-sulfide stability boundary. Its significance increases in regimes with relatively high dissolved Fe:S ratios, which explains its occurrence in freshwater sediments and iron-enriched marine sediments. It is also a paleoenvironmental marker for transitional environments, especially between freshwater and marine systems. It is stable relative to pyrrhotite and smythite, although their formation together with greigite in low pe environments may be facilitated by catalytic processes. The greigite-smythite (pyrrhotite)-siderite association is a potential marker for ancient methanogenesis. Greigite is relatively sensitive to oxidation and its long-term geological preservation depends mostly on protection from oxidation by low sediment permeability or enclosure in other minerals or organic remains. Most sedimentary and biological greigite forms via equilibrium reactions involving mackinawite-like precursors, with no direct coupling of greigite with pyrite; these minerals form independently during sedimentary diagenesis. Magnetosomal greigite production by magnetotactic bacteria is a consequence of relative greigite stability, its decoupling from pyrite, and its protection from oxidation by cell membranes.

Formation and preservation mechanisms of magnetofossils in the surface sediments of muddy areas in the yellow and Bohai Seas, China

Magnetofossils in the continental shelf sediments of the Yellow and Bohai Seas have long been overlooked. Based on the magnetic results of 88 surface sediments (0–10 cm depth), first-order reversal curve (FORC) diagrams, isothermal remanent magnetization (IRM) acquisition curves from 6 representative samples, and transmission electron microscopy (TEM) observations of 2 samples, the formation and preservation mechanisms of magnetofossils in this region are elucidated. The FORC diagrams consistently show a clear central ridge feature, which indicates the presence of intact magnetofossils in all representative samples. The morphologies observed by TEM are primarily equant and elongated, with minimal or no bullet-shaped (magnetite) magnetofossils. Analysis further reveals a widespread distribution of magnetofossils in the mud areas of the Bohai Sea, North Yellow Sea, and South Yellow Sea, with proportions (contribution to SIRM; SIRM is defined as the remanent magnetization that remains constant as the external magnetic field increases) of <32.5 %, 40.9 % ∼ 44.6 %, and 59.9 % ∼ 66.5 %, respectively. Despite the presence of non-biogenic single domain magnetite, the proportion of magnetofossils can be estimated by the χARM/SIRM value, as they are positively correlated. The surface sedimentary environment of these mud areas is primarily suboxic and characterized by abundant dissolved iron, which facilitate the formation of magnetofossils by magnetotactic bacteria (MTB). It is unlikely that the surface sedimentary environment becomes sulphidic, thereby enabling the preservation of magnetofossils after their formation. The redox state of the study area, crucial for magnetofossil formation, is mainly controlled by the total organic carbon (TOC) content. From north to south, the higher proportion of magnetofossils is coupled with higher TOC content, possibly due to the intensified reducing degree of the suboxic environment, promoting MTB proliferation and thus forming more magnetofossils. The mechanisms governing the formation and preservation of magnetofossils proposed in this study may also be applicable to geological records.

Active string fluids and gels formed by dipolar active Brownian particles in 3D.

Self-propelled particles possessing permanent magnetic dipole moments occur naturally in magnetotactic bacteria and can be built into man-made systems such as active colloids or micro-robots. Yet, the interplay between self-propulsion and anisotropic dipole-dipole interactions on dynamic self-assembly in three dimensions (3D) remains poorly understood. We conduct Brownian dynamics simulations of active dipolar particles in 3D, focusing on the low-density regime, where dipolar hard spheres tend to form chain-like aggregates and percolated networks with increasing dipolar coupling strength. We find that strong active forces override dipolar attractions, effectively inhibiting chain-like aggregation and network formation. Conversely, activating particles with low to moderate forces results in a fluid composed of active chains and rings. At strong dipolar coupling strengths, this active fluid transitions into an active gel, consisting of a percolated network of active chains. Although the overall structure of the active gel remains interconnected, the network experiences more frequent configurational rearrangements due to the reduced bond lifetime of active dipolar particles. Consequently, particles exhibit enhanced translational and rotational diffusion within the active fluid of strings and active gels compared to their passive counterparts. We quantify the influence of activity on aggregate topology as they transition from branched structures to unconnected chains and rings. Our findings are summarized in a state diagram, delineating the impact of dipolar coupling strength and active force magnitude on the system.

Temporal and spatial resolution of magnetosome degradation at the subcellular level in a 3D lung carcinoma model

Magnetic nanoparticles offer many exciting possibilities in biomedicine, from cell imaging to cancer treatment. One of the currently researched nanoparticles are magnetosomes, magnetite nanoparticles of high chemical purity synthesized by magnetotactic bacteria. Despite their therapeutic potential, very little is known about their degradation in human cells, and even less so of their degradation within tumours. In an effort to explore the potential of magnetosomes for cancer treatment, we have explored their degradation process in a 3D human lung carcinoma model at the subcellular level and with nanometre scale resolution. We have used state of the art hard X-ray probes (nano-XANES and nano-XRF), which allow for identification of distinct iron phases in each region of the cell. Our results reveal the progression of magnetite oxidation to maghemite within magnetosomes, and the biosynthesis of magnetite and ferrihydrite by ferritin.Graphical

Screening, Isolation and Characterization of Aerobic Magnetotactic Bacteria From Western Ghats Forest Soil.

The online version contains supplementary material available at 10.1007/s12088-024-01316-4.

Tumor Microenvironment-Responsive Magnetotactic Bacteria-Based Multi-Drug Delivery Platform for MRI-Visualized Tumor Photothermal Chemodynamic Therapy.

Cancer cells display elevated reactive oxygen species (ROS) and altered redox status. Herein, based on these characteristics, we present a multi-drug delivery platform, AMB@PDAP-Fe (APPF), from the magnetotactic bacterium AMB-1 and realize MRI-visualized tumor-microenvironment-responsive photothermal-chemodynamic therapy. The Fe3+ in PDAP-Fe is reduced by the GSH at the tumor site and is released in the form of highly active Fe2+, which catalyzes the generation of ROS through the Fenton reaction and inhibits tumor growth. At the same time, the significant absorption of the mineralized magnetosomes in AMB-1 cells in the NIR region enables them to efficiently convert near-infrared light into heat energy for photothermal therapy (PTT), to which PDAP also contributes. The heat generated in the PTT process accelerates the process of Fe2+ release, thereby achieving an enhanced Fenton reaction in the tumor microenvironment. In addition, the magnetosomes in AMB-1 are used as an MRI contrast agent, and the curing process is visualized. This tumor microenvironment-responsive MTB-based multi-drug delivery platform displays the potency to combat tumors and demonstrates the utility and practicality of understanding the cooperative molecular mechanism when designing multi-drug combination therapies.

Insights Into a Correlation Between Magnetotactic Bacteria and Polymetallic Nodule Distribution in the Eastern Central Pacific Ocean

AbstractThe Clarion–Clipperton Fracture Zone (CCFZ) in the eastern central Pacific Ocean is the world's largest area for potential deep‐sea polymetallic nodule mining and is attracting increased scientific and commercial interest. Recent studies indicate that biogenic magnetite, generated intracellularly by magnetotactic bacteria (MTB), can carry a biogeochemical remanent magnetization in polymetallic nodules, although whether biogenic or physical‐chemical processes are responsible for nodule formation remain poorly constrained. Here, we report a combination of magnetic, electron microscope and geochemical analyses on seafloor surface sediments from the eastern CCFZ to understand the spatial distribution of biogenic magnetite and possible relationships between MTB and polymetallic nodules. Experimental results indicate that sedimentary magnetic minerals from the northern and southern regions are dominated by detrital (eolian loess and volcanic material) and biogenic magnetic minerals (magnetosomes), respectively. Sediments from the intermediate region contain both detrital and biogenic magnetic minerals. Quantitative first‐order reversal curve‐principal component analysis indicates that biogenic magnetite has the highest concentration in the intermediate CCFZ region, coincident with the highest polymetallic nodule density. Combined with previous research, we speculate that MTB growth on the CCFZ seafloor is driven mainly by local redox conditions. Manganese nodule surfaces are rich in organic biofilms, which results in a relatively thick oxic‐anoxic transition zone in high‐abundance manganese nodule regions, which generates an optimal microenvironment for both MTB growth and magnetite biomineralization. This study provides new clues for understanding the ecological distribution of MTB and the biogeochemical remanent magnetization recorded by biogenic magnetite in deep‐sea sediments.

Artificial magnetosomes: Molecularly restructured SPIONs with enhanced potential for magnetic imaging

Magnetosomes represent an elegant example of ultrastable nanomaterials that nature produces by encapsulating magnetic nanoparticles in liposomal sub-compartments of magnetotactic bacteria. Materials chemists continue to strive for ways to mimic the performance of natural systems, but the artificial synthesis of magnetosomes remains unrealized. Here, we report molecular restructuring of the surface of oleic-acid-capped superparamagnetic iron oxide nanoparticles (SPIONs) to produce magnetosomes. Our strategy involves the use of triethylamine as an amphiphilic surfactant that through a combination of ligand exchange and rearrangement mechanisms, facilitates an organic-to-aqueous phase transfer of SPIONs while turning them into magnetosomes. These liposome-encapsulated SPIONs showed dynamic aqueous stability alongside noticeably improved magnetic properties. This improved their performance as contrast agents for magnetic resonance imaging (MRI) and magnetic particle imaging (MPI), the latter revealing a 33.5 % improvement in signal sensitivity over the original SPIONs. The presented strategy is extendable to prepare liposomal dispersions of other biomedically important nanomaterials.

Magnetic imaging of individual magnetosome chains in magnetotactic bacteria

While significant advances have been made in exploring and uncovering the promising potential of biomagnetic materials, persistent challenges remain on various fronts, notably in the characterization of individual elements. This study makes use of advanced modes of Magnetic Force Microscopy (MFM) and tailored MFM probes to characterize individual magnetotactic bacteria in different environments. The characterization of these elements posed a significant challenge, as the magnetosomes, besides presenting low magnetic signal, are embedded in bacteria of much larger size. To overcome this, customed Atomic Force Microscopy probes are developed through various strategies, enhancing sensitivity in different environments, including liquids. Furthermore, employing MFM imaging under an in-situ magnetic field provides an opportunity to gather quantitative data regarding the critical fields of these individual chains of nanoparticles. This approach marks a substantial advancement in the field of MFM for biological applications, enabling the detection of magnetosomes under different conditions.

High-yield magnetosome production of Magnetospirillum magneticum strain AMB-1 in flask fermentation through simplified processing and optimized iron supplementation.

Developing a simplified flask fermentation strategy utilizing magnetotactic bacterium AMB-1 and optimized iron supplementation for high-yield magnetosome production to address the challenges associated with magnetosome acquisition. A reliable processing for the pure culture of AMB-1 was established using standard laboratory consumables and equipment. Subsequently, the medium and iron supplementation were optimized to enhance the yield of AMB-1 magnetosomes. The mSLM supported higher biomass accumulation in flask fermentation, reaching an OD565 of ~ 0.7. The premixed solution of ferric quinate and EDTA-Fe (at a ratio of 0.5:0.5 and a concentration of 0.4mmol/L) stabilized Fe3+ and significantly increased the reductase activity of AMB-1. Flask fermentations with an initial volume of 15 L were then conducted employing the optimized fermentation strategy. After two rounds of iron and nutrient supplementation, the magnetosome yield reached 185.7 ± 9.5mg/batch (approximately 12mg/L), representing the highest AMB-1 flask fermentation yield to our knowledge. A flask fermentation strategy for high-yield magnetsome production was developed, eliminating the need for bioreactors and greatly simplifying the process of magnetosome acquisition.

Discovery of giant and conventional magnetofossils bookending Cretaceous Oceanic Anoxic Event 2

Conventional magnetofossils are the remains of magnetotactic bacteria and giant magnetofossils are the remains of iron biomineralizing organisms that have not yet been identified. We report the oldest robust conventional and giant magnetofossil records, ~97 Ma, from marine sediments drilled in Holland Park, Virginia, USA. The Holland Park core records the Cenomanian-Turonian boundary and Oceanic-Anoxic Event 2 (OAE2). Magnetic datasets indicate single domain magnetite within the clay-rich sediments bookending OAE2. Electron microscopy images from these intervals highlight conventional and giant magnetofossil morphologies, including three potentially new giant magnetofossil morphologies: seeds, squash, and spades. There is an overall high abundance and morphological disparity of magnetofossils at Holland Park. However, we observe abundance, disparity, and preservation changes between the magnetofossil assemblages bookending OAE2. Our observations provide clues toward understanding the ecological thresholds of the enigmatic organisms that produce giant magnetofossils and evidence that magnetofossils may be widely distributed in the geologic record.