A thermophilic chemolithoautotrophic bacterial consortium suggests a mutual relationship between bacteria in extreme oligotrophic environments.

A thermophilic, chemolithoautotrophic, and aerobic microbial consortium (termed carbonitroflex) growing in a nutrient-poor medium and an atmosphere containing N2, O2, CO2, and CO is investigated as a model to expand our understanding of extreme biological systems. Here we show that the consortium is dominated by Carbonactinospora thermoautotrophica (strain StC), followed by Sphaerobacter thermophilus, Chelatococcus spp., and Geobacillus spp. Metagenomic analysis of the consortium reveals a mutual relationship among bacteria, with C. thermoautotrophica StC exhibiting carboxydotrophy and carbon-dioxide storage capacity. C. thermoautotrophica StC, Chelatococcus spp., and S. thermophilus harbor genes encoding CO dehydrogenase and formate oxidase. No pure cultures were obtained under the original growth conditions, indicating that a tightly regulated interactive metabolism might be required for group survival and growth in this extreme oligotrophic system. The breadwinner hypothesis is proposed to explain the metabolic flux model and highlight the vital role of C. thermoautotrophica StC (the sole keystone species and primary carbon producer) in the survival of all consortium members. Our data may contribute to the investigation of complex interactions in extreme environments, exemplifying the interconnections and dependency within microbial communities.

Simultaneous lipase production and immobilization: morphology and physiology study of Penicillium simplicissimum in submerged and solid-state fermentation with polypropylene as an inert support.

The influence of different carbon sources (glucose (G), olive oil (O), and a combination of both (GO)) in the physiology (biomass and lipase production) and morphology (light and environmental and scanning electron microscopy) of the fungus Penicillium simplicissimum by applying submerged (SmF) and solid-state (SSF) fermentations was investigated. The cultivation was carried out using polypropylene as hydrophobic inert support in SmF and SSF to understand better the influence of a support for the fungus growth and also provides the immobilization of lipases during its production. Micrographs show different morphologies: in SSF, the fungus grows on and inside the inert support independent of the media; in SmF, the formation of high-density spherical pellets obtained in medium GO leads to the best productivity and specific product yield Yp/x..Conidiation is observed mainly in SSF, a few in SmF with polypropylene as inert support and not in SmF, which may indicate a stress condition in SSF. Possibly, the morphology acquired by the fungus under stressful conditions may be the key to the higher biomass and lipase productivity at SSF. The developed process with simultaneous production and immobilization of lipase leads to a new promissory biocatalyst once it can be directly applied with no need for downstream processes.

Occurrence of south- and north-seeking multicellular magnetotactic prokaryotes in a coastal lagoon in the South Hemisphere / Presencia de procariotatos magnetotácticos multicelulares que buscan el sur y el norte en una laguna costera del hemisferio sur

Magnetotactic bacteria (MTB) response to the magnetic field can be classified into north-seeking (NS) and south-seeking (SS), which usually depends on their inhabiting site in the North and South Hemisphere, respectively. However, uncommon inverted polarity was observed on both hemispheres. Here, we studied magnetotactic multicellular prokaryotes (MMPs) from a coastal lagoon in Brazil collected in April and August 2014. MMPs from the first sampling period presented both magnetotactic behaviors, while MMPs collected in August/2014 were only SS. Phylogenetic analysis based on the 16S rRNA coding gene showed that these organisms belong to the Deltaproteobacteria class. The 16S rRNA gene sequences varied among MMPs regardless of the sampling period, and similarity values were not related to the type of magnetotactic response presented by the microorganisms. Therefore, differences in the magnetotactic behavior might result from the physiological state of MMPs, the availability of resources, or the instability of the chemical gradient in the environment. This is the first report of NS magnetotactic behavior on MMPs from the South Hemisphere.(AU)

Occurrence of south- and north-seeking multicellular magnetotactic prokaryotes in a coastal lagoon in the South Hemisphere.

Magnetotactic bacteria (MTB) response to the magnetic field can be classified into north-seeking (NS) and south-seeking (SS), which usually depends on their inhabiting site in the North and South Hemisphere, respectively. However, uncommon inverted polarity was observed on both hemispheres. Here, we studied magnetotactic multicellular prokaryotes (MMPs) from a coastal lagoon in Brazil collected in April and August 2014. MMPs from the first sampling period presented both magnetotactic behaviors, while MMPs collected in August/2014 were only SS. Phylogenetic analysis based on the 16S rRNA coding gene showed that these organisms belong to the Deltaproteobacteria class. The 16S rRNA gene sequences varied among MMPs regardless of the sampling period, and similarity values were not related to the type of magnetotactic response presented by the microorganisms. Therefore, differences in the magnetotactic behavior might result from the physiological state of MMPs, the availability of resources, or the instability of the chemical gradient in the environment. This is the first report of NS magnetotactic behavior on MMPs from the South Hemisphere.

Magnetosome magnetite biomineralization in a flagellated protist: evidence for an early evolutionary origin for magnetoreception in eukaryotes.

The most well-recognized magnetoreception behaviour is that of the magnetotactic bacteria (MTB), which synthesize membrane-bounded magnetic nanocrystals called magnetosomes via a biologically controlled process. The magnetic minerals identified in prokaryotic magnetosomes are magnetite (Fe3 O4 ) and greigite (Fe3 S4 ). Magnetosome crystals, regardless of composition, have consistent, species-specific morphologies and single-domain size range. Because of these features, magnetosome magnetite crystals possess specific properties in comparison to abiotic, chemically synthesized magnetite. Despite numerous discoveries regarding MTB phylogeny over the last decades, this diversity is still considered underestimated. Characterization of magnetotactic microorganisms is important as it might provide insights into the origin and establishment of magnetoreception in general, including eukaryotes. Here, we describe the magnetotactic behaviour and characterize the magnetosomes from a flagellated protist using culture-independent methods. Results strongly suggest that, unlike previously described magnetotactic protists, this flagellate is capable of biomineralizing its own anisotropic magnetite magnetosomes, which are aligned in complex aggregations of multiple chains within the cell. This organism has a similar response to magnetic field inversions as MTB. Therefore, this eukaryotic species might represent an early origin of magnetoreception based on magnetite biomineralization. It should add to the definition of parameters and criteria to classify biogenic magnetite in the fossil record.

Uptake and persistence of bacterial magnetite magnetosomes in a mammalian cell line: Implications for medical and biotechnological applications.

Magnetotactic bacteria biomineralize intracellular magnetic nanocrystals surrounded by a lipid bilayer called magnetosomes. Due to their unique characteristics, magnetite magnetosomes are promising tools in Biomedicine. However, the uptake, persistence, and accumulation of magnetosomes within mammalian cells have not been well studied. Here, the endocytic pathway of magnetite magnetosomes and their effects on human cervix epithelial (HeLa) cells were studied by electron microscopy and high spatial resolution nano-analysis techniques. Transmission electron microscopy of HeLa cells after incubation with purified magnetosomes showed the presence of magnetic nanoparticles inside or outside endosomes within the cell, which suggests different modes of internalization, and that these structures persisted beyond 120 h after internalization. High-resolution transmission electron microscopy and electron energy loss spectra of internalized magnetosome crystals showed no structural or chemical changes in these structures. Although crystal morphology was preserved, iron oxide crystalline particles of approximately 5 nm near internalized magnetosomes suggests that minor degradation of the original mineral structures might occur. Cytotoxicity and microscopy analysis showed that magnetosomes did not result in any apparent effect on HeLa cells viability or morphology. Based on our results, magnetosomes have significant biocompatibility with mammalian cells and thus have great potential in medical, biotechnological applications.

Association of magnetotactic multicellular prokaryotes with Pseudoalteromonas species in a natural lagoon environment.

Magnetotactic bacteria, for the most part, are free-living, motile, unicellular prokaryotes that inhabit almost all marine and freshwater environments. One notable exception to the unicellular mode, however, are the magnetotactic multicellular prokaryotes. These morphologically unique prokaryotes (e.g., Candidatus Magnetoglobus multicellularis) are motile aggregates of 20-40 genetically identical, Gram-negative cells organised as a sphere (or ovoid in shape) and only motile as a unit. No specific close physical association between magnetotactic bacteria and non-magnetotactic microorganisms has ever been reported. Here, using culture-independent approaches, we show an unusual association between the spherical magnetotactic multicellular prokaryote Ca. Magnetoglobus multicellularis and Pseudoalteromonas species in environmental sediment and water samples collected from the Araruama Lagoon in Brazil. Cells of Pseudoalteromonas species were observed to be physically attached to the surface and, notably, even in the intercellular space of these spherical magnetotactic multicellular prokaryotes. An attempt to correlate the frequency of association between Pseudoalteromonas and magnetotactic multicellular prokaryotes with sediment depth was made but only a slight decrease in the number of Pseudoalteromonas cells per magnetotactic multicellular prokaryote was observed with increasing depth. Similar observations were made with magnetotactic multicellular prokaryotes from another Brazilian Lagoon (Rodrigo de Freitas) and the putative symbiont/parasite was detected. Although our results suggest some sort of specificity in the relationship between these prokaryotes, the precise nature of this association remains unclear.

Culture-independent characterization of a novel magnetotactic member affiliated to the Beta class of the Proteobacteria phylum from an acidic lagoon.

Magnetotactic bacteria (MTB) comprise a group of motile microorganisms common in most mesothermal aquatic habitats with pH values around neutrality. However, during the last two decades, a number of MTB from extreme environments have been characterized including: cultured alkaliphilic strains belonging to the Deltaproteobacteria class of the Proteobacteria phylum; uncultured moderately thermophilic strains belonging to the Nitrospirae phylum; cultured and uncultured moderately halophilic or strongly halotolerant bacteria affiliated with the Deltaproteobacteria and Gammaproteobacteria classes and an uncultured psychrophilic species belonging to the Alphaproteobacteria class. Here, we used culture-independent techniques to characterize MTB from an acidic freshwater lagoon in Brazil (pH ∼ 4.4). MTB morphotypes found in this acidic lagoon included cocci, rods, spirilla and vibrioid cells. Magnetite (Fe3 O4 ) was the only mineral identified in magnetosomes of these MTB while magnetite magnetosome crystal morphologies within the different MTB cells included cuboctahedral (present in spirilla), elongated prismatic (present in cocci and vibrios) and bullet-shaped (present in rod-shaped cells). Intracellular pH measurements using fluorescent dyes showed that the cytoplasmic pH was close to neutral in most MTB cells and acidic in some intracellular granules. Based on 16S rRNA gene phylogenetic analyses, some of the retrieved gene sequences belonged to the genus Herbaspirillum within the Betaproteobacteria class of the Proteobacteria phylum. Fluorescent in situ hybridization using a Herbaspirillum-specific probe hybridized with vibrioid MTB in magnetically-enriched samples. Transmission electron microscopy of the Herbaspirillum-like MTB revealed the presence of many intracellular granules and a single chain of elongated prismatic magnetite magnetosomes. Diverse populations of MTB have not seemed to have been described in detail in an acid environment. In addition, this is the first report of an MTB phylogenetically affiliated with Betaproteobacteria class.

Localized iron accumulation precedes nucleation and growth of magnetite crystals in magnetotactic bacteria.

Many magnetotactic bacteria (MTB) biomineralize magnetite crystals that nucleate and grow inside intracellular membranous vesicles that originate from invaginations of the cytoplasmic membrane. The crystals together with their surrounding membranes are referred to magnetosomes. Magnetosome magnetite crystals nucleate and grow using iron transported inside the vesicle by specific proteins. Here we address the question: can iron transported inside MTB for the production of magnetite crystals be spatially mapped using electron microscopy? Cultured and uncultured MTB from brackish and freshwater lagoons were studied using analytical transmission electron microscopy in an attempt to answer this question. Scanning transmission electron microscopy was used at sub-nanometric resolution to determine the distribution of elements by implementing high sensitivity energy dispersive X-ray (EDS) mapping and electron energy loss spectroscopy (EELS). EDS mapping showed that magnetosomes are enmeshed in a magnetosomal matrix in which iron accumulates close to the magnetosome forming a continuous layer visually appearing as a corona. EELS, obtained at high spatial resolution, confirmed that iron was present close to and inside the lipid bilayer magnetosome membrane. This study provides important clues to magnetite formation in MTB through the discovery of a mechanism where iron ions accumulate prior to magnetite biomineralization.

Surface imaging of the filamentous fungus Penicillium simplicissimum growing in a solid-state fermentation system.

A comparative study on the lipase-producing fungus Penicillium simplissicimum, grown on a tray type solid-state fermentation (SSF) bioreactor, was performed using stereoscopy, focus Z-stacking stereoscopic images, field emission scanning electron microscopy (FE-SEM) and environmental scanning electron microscopy (ESEM) to better characterize the morphology of filamentous fungi in SSF and their distribution over the solid matrix. The imaging of live fungal samples using a stereomicroscope with focus Z-stacking showed differences in colonization between a static SSF and an intermittent agitated SSF. A comparison of the stereomicroscopy, hi-vacuum and environmental scanning electron microscopy results obtained using different protocols for sample processing showed that fixation with osmium tetroxide vapor and subsequent hydrated imaging is the best combination of sample preparation and imaging conditions for keeping the arrangement of the aerial hyphae and conidia morphology closer to the natural state. These combined methodologies can be applied in the SSF of fungal growth to characterize the formation of conidiophores over time, the conidia morphology and the spatial organization after their release from conidiophores. Mycelium colonization over the matrix, which is an important characteristic related to the production of different biotechnological products, could be observed and provide more knowledge about fungal physiology behavior during SSF.

Broadcast Spawning Coral Mussismilia hispida Can Vertically Transfer its Associated Bacterial Core.

The hologenome theory of evolution (HTE), which is under fierce debate, presupposes that parts of the microbiome are transmitted from one generation to the next [vertical transmission (VT)], which may also influence the evolution of the holobiont. Even though bacteria have previously been described in early life stages of corals, these early life stages (larvae) could have been inoculated in the water and not inside the parental colony (through gametes) carrying the parental microbiome. How Symbiodinium is transmitted to offspring is also not clear, as only one study has described this mechanism in spawners. All other studies refer to incubators. To explore the VT hypothesis and the key components being transferred, colonies of the broadcast spawner species Mussismilia hispida were kept in nurseries until spawning. Gamete bundles, larvae and adult corals were analyzed to identify their associated microbiota with respect to composition and location. Symbiodinium and bacteria were detected by sequencing in gametes and coral planula larvae. However, no cells were detected using microscopy at the gamete stage, which could be related to the absence of those cells inside the oocytes/dispersed in the mucus or to a low resolution of our approach. A preliminary survey of Symbiodinium diversity indicated that parental colonies harbored Symbiodinium clades B, C and G, whereas only clade B was found in oocytes and planula larvae [5 days after fertilization (a.f.)]. The core bacterial populations found in the bundles, planula larvae and parental colonies were identified as members of the genera Burkholderia, Pseudomonas, Acinetobacter, Ralstonia, Inquilinus and Bacillus, suggesting that these populations could be vertically transferred through the mucus. The collective data suggest that spawner corals, such as M. hispida, can transmit Symbiodinium cells and the bacterial core to their offspring by a coral gamete (and that this gamete, with its bacterial load, is released into the water), supporting the HTE. However, more data are required to indicate the stability of the transmitted populations to indicate whether the holobiont can be considered a unit of natural selection or a symbiotic assemblage of independently evolving organisms.

Ultrastructure of ellipsoidal magnetotactic multicellular prokaryotes depicts their complex assemblage and cellular polarity in the context of magnetotaxis.

Magnetotactic multicellular prokaryotes (MMPs) consist of unique microorganisms formed by genetically identical Gram-negative bacterial that live as a single individual capable of producing magnetic nano-particles called magnetosomes. Two distinct morphotypes of MMPs are known: spherical MMPs (sMMPs) and ellipsoidal MMPs (eMMPs). sMMPs have been extensively characterized, but less information exists for eMMPs. Here, we report the ultrastructure and organization as well as gene clusters responsible for magnetosome and flagella biosynthesis in the magnetite magnetosome producer eMMP Candidatus Magnetananas rongchenensis. Transmission electron microscopy and focused ion beam scanning electron microscopy (FIB-SEM) 3D reconstruction reveal that cells with a conspicuous core-periphery polarity were organized around a central space. Magnetosomes were organized in multiple chains aligned along the periphery of each cell. In the partially sequenced genome, magnetite-related mamAB gene and mad gene clusters were identified. Two cell morphologies were detected: irregular elliptical conical 'frustum-like' (IECF) cells and H-shaped cells. IECF cells merge to form H-shaped cells indicating a more complex structure and possibly a distinct evolutionary position of eMMPs when compared with sMMPs considering multicellularity.

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.

Draft Genome Sequence of Magnetovibrio blakemorei Strain MV-1, a Marine Vibrioid Magnetotactic Bacterium.

We report here the genome sequence of Magnetovibrio blakemorei MV-1, a marine vibrioid magnetotactic bacterium with a single polar flagellum. The current assembly consists of 91 contigs with a combined size of 3,638,804 bp (54.3% G+C content). This genome allows for further investigations of the molecular biomineralization mechanisms of magnetosome formation.

Combined genomic and structural analyses of a cultured magnetotactic bacterium reveals its niche adaptation to a dynamic environment.

BACKGROUND: Magnetotactic bacteria (MTB) are a unique group of prokaryotes that have a potentially high impact on global geochemical cycling of significant primary elements because of their metabolic plasticity and the ability to biomineralize iron-rich magnetic particles called magnetosomes. Understanding the genetic composition of the few cultivated MTB along with the unique morphological features of this group of bacteria may provide an important framework for discerning their potential biogeochemical roles in natural environments. RESULTS: Genomic and ultrastructural analyses were combined to characterize the cultivated magnetotactic coccus Magnetofaba australis strain IT-1. Cells of this species synthesize a single chain of elongated, cuboctahedral magnetite (Fe3O4) magnetosomes that cause them to align along magnetic field lines while they swim being propelled by two bundles of flagella at velocities up to 300 µm s-1. High-speed microscopy imaging showed the cells move in a straight line rather than in the helical trajectory described for other magnetotactic cocci. Specific genes within the genome of Mf. australis strain IT-1 suggest the strain is capable of nitrogen fixation, sulfur reduction and oxidation, synthesis of intracellular polyphosphate granules and transporting iron with low and high affinity. Mf. australis strain IT-1 and Magnetococcus marinus strain MC-1 are closely related phylogenetically although similarity values between their homologous proteins are not very high. CONCLUSION: Mf. australis strain IT-1 inhabits a constantly changing environment and its complete genome sequence reveals a great metabolic plasticity to deal with these changes. Aside from its chemoautotrophic and chemoheterotrophic metabolism, genomic data indicate the cells are capable of nitrogen fixation, possess high and low affinity iron transporters, and might be capable of reducing and oxidizing a number of sulfur compounds. The relatively large number of genes encoding transporters as well as chemotaxis receptors in the genome of Mf. australis strain IT-1 combined with its rapid swimming velocities, indicate that cells respond rapidly to environmental changes.

North-Seeking Magnetotactic Gammaproteobacteria in the Southern Hemisphere.

UNLABELLED: Magnetotactic bacteria (MTB) comprise a phylogenetically diverse group of prokaryotes capable of orienting and navigating along magnetic field lines. Under oxic conditions, MTB in natural environments in the Northern Hemisphere generally display north-seeking (NS) polarity, swimming parallel to the Earth's magnetic field lines, while those in the Southern Hemisphere generally swim antiparallel to magnetic field lines (south-seeking [SS] polarity). Here, we report a population of an uncultured, monotrichously flagellated, and vibrioid MTB collected from a brackish lagoon in Brazil in the Southern Hemisphere that consistently exhibits NS polarity. Cells of this organism were mainly located below the oxic-anoxic interface (OAI), suggesting it is capable of some type of anaerobic metabolism. Magnetosome crystalline habit and composition were consistent with elongated prismatic magnetite (Fe3O4) particles. Phylogenetic analysis based on 16S rRNA gene sequencing indicated that this organism belongs to a distinct clade of the Gammaproteobacteria class. The presence of NS MTB in the Southern Hemisphere and the previously reported finding of SS MTB in the Northern Hemisphere reinforce the idea that magnetotaxis is more complex than we currently understand and may be modulated by factors other than O2 concentration and redox gradients in sediments and water columns. IMPORTANCE: Magnetotaxis is a navigational mechanism used by magnetotactic bacteria to move along geomagnetic field lines and find an optimal position in chemically stratified sediments. For that, magnetotactic bacteria swim parallel to the geomagnetic field lines under oxic conditions in the Northern Hemisphere, whereas those in the Southern Hemisphere swim antiparallel to magnetic field lines. A population of uncultured vibrioid magnetotactic bacteria was discovered in a brackish lagoon in the Southern Hemisphere that consistently swim northward, i.e., the opposite of the overwhelming majority of other Southern Hemisphere magnetotactic bacteria. This finding supports the idea that magnetotaxis is more complex than previously thought.

Culture-independent characterization of novel psychrophilic magnetotactic cocci from Antarctic marine sediments.

Magnetotactic bacteria (MTB) are a heterogeneous group of ubiquitous aquatic microorganisms capable of biomineralizing nano-sized, membrane-bound, magnetic iron-rich mineral particles called magnetosomes. MTB are found in chemically-stratified aquatic sediments and/or water columns with a wide range of salinities, moderate to high temperatures, and pH varying from neutral to strongly alkaline. MTB from very cold environments have not been investigated to any great degree and here we characterize MTB from the low temperature Antarctic maritime region. Sediment samples were collected at nine sampling sites within Admiralty Bay, King George Island (62°23'S 58°27'W) from 2009 to 2013. Samples from five sites contained MTB and those from two of these sites contained large number of magnetotactic cocci that were studied using electron microscopy and molecular techniques. The magnetotactic cocci contained magnetosomes either arranged as two or four chains or as a disorganized cluster. The crystalline habit and composition of all magnetosomes analyzed with high-resolution transmission electron microscopy and energy dispersive X-ray microanalysis were consistent with elongated prismatic crystals of magnetite (Fe3 O4 ). The retrieved 16S rRNA gene sequences from magnetically-enriched magnetotactic cocci clustered into three distinct groups affiliated with the Alphaproteobacteria class of the Proteobacteria. Novel sequences of each phylogenetic cluster were confirmed using fluorescent in situ hybridization. Metagenomic data analysis of magnetically-enriched magnetotactic cocci revealed the presence of mam genes and MTB-specific hypothetical protein coding genes. Sequence homology and phylogenetic analysis indicated that predicted proteins are related to those of cultivated alphaproteobacterial MTB. The consistent and continuous low temperature of the sediment where the magnetotactic cocci are present (always below 1°C) suggests that these MTB from maritime Antarctica are psychrophiles. Moreover, similar morphotypes and 16S gene sequences were retrieved from samples collected from different sites from maritime Antarctica for several years suggesting that these new strains of MTB are indigenous members of Antarctic microbiota.

Magnetotactic bacteria as potential sources of bioproducts.

Magnetotactic bacteria (MTB) produce intracellular organelles called magnetosomes which are magnetic nanoparticles composed of magnetite (Fe3O4) or greigite (Fe3S4) enveloped by a lipid bilayer. The synthesis of a magnetosome is through a genetically controlled process in which the bacterium has control over the composition, direction of crystal growth, and the size and shape of the mineral crystal. As a result of this control, magnetosomes have narrow and uniform size ranges, relatively specific magnetic and crystalline properties, and an enveloping biological membrane. These features are not observed in magnetic particles produced abiotically and thus magnetosomes are of great interest in biotechnology. Most currently described MTB have been isolated from saline or brackish environments and the availability of their genomes has contributed to a better understanding and culturing of these fastidious microorganisms. Moreover, genome sequences have allowed researchers to study genes related to magnetosome production for the synthesis of magnetic particles for use in future commercial and medical applications. Here, we review the current information on the biology of MTB and apply, for the first time, a genome mining strategy on these microorganisms to search for secondary metabolite synthesis genes. More specifically, we discovered that the genome of the cultured MTB Magnetovibrio blakemorei, among other MTB, contains several metabolic pathways for the synthesis of secondary metabolites and other compounds, thereby raising the possibility of the co-production of new bioactive molecules along with magnetosomes by this species.

Ferromagnetic resonance of intact cells and isolated crystals from cultured and uncultured magnetite-producing magnetotactic bacteria.

Most magnetotactic bacteria (MB) produce stable, single-domain magnetite nanocrystals with species-specific size, shape and chain arrangement. In addition, most crystals are elongated along the [111] direction, which is the easy axis of magnetization in magnetite, chemically pure and structurally perfect. These special characteristics allow magnetite crystal chains from MB to be recognized in environmental samples including old sedimentary rocks. Ferromagnetic resonance (FMR) has been proposed as a powerful and practical tool for screening large numbers of samples possibly containing magnetofossils. Indeed, several studies were recently published on FMR of cultured MB, mainly Magnetospirillum gryphiswaldense. In this work, we examined both uncultured magnetotactic cocci and the cultured MB M. gryphiswaldense using transmission electron microscopy (TEM) and FMR from 10 K to room temperature (RT). The TEM data supported the FMR spectral characteristics of our samples. The FMR spectra of both bacteria showed the intrinsic characteristics of magnetite produced by MB, such as extended absorption at the low field region of the spectra and a Verwey transition around 100 K. As previously observed, the spectra of M. gryphiswaldense isolated crystals were more symmetrical than the spectra obtained from whole cells, reflecting the loss of chain arrangement due to the small size and symmetrical shape of the crystals. However, the FMR spectra of magnetic crystals isolated from magnetotactic cocci were very similar to the FMR spectra of whole cells, because the chain arrangement was maintained due to the large size and prismatic shape of the crystals. Our data support the use of FMR spectra to detect magnetotactic bacteria and magnetofossils in samples of present and past environments. Furthermore, the spectra suggest the use of the temperature transition of spectral peak-to-peak intensity to obtain the Verwey temperature for these systems.