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.

Uncovering the hidden complexity of multicellular magnetotactic bacteria.

Multicellular magnetotactic bacteria (MMB) have a surprisingly complex multicellular lifestyle. A new study in PLOS Biology combines genomics, microscopy, and isotopic labeling to show that MMB form obligately multicellular consortia of genetically diverse cells with rudimentary division of labor.

Primordial magnetotaxis in putative giant paleoproterozoic magnetofossils.

Magnetotactic bacteria produce chains of nanoscopic iron minerals used for navigation, which can be preserved over geological timescales in the form of magnetofossils. Micrometer-sized magnetite crystals with unusual shapes suggesting a biologically controlled mineralization have been found in the geological record and termed giant magnetofossils. The biological origin and function of giant magnetofossils remains unclear, due to the lack of modern analogues to giant magnetofossils. Using distinctive Ptychographic nanotomography data of Precambrian (1.88 Ga) rocks, we recovered the morphology of micrometric cuboid grains of iron oxides embedded in an organic filamentous fossil to construct synthetic magnetosomes. Their morphology is different from that of previously found giant magnetofossils, but their occurrence in filamentous microfossils and micromagnetic simulations support the hypothesis that they could have functioned as a navigation aid, akin to modern magnetosomes.

Discovery of antibacterial biogenic magnetosome nanoparticles from Providencia sp. MTBPRB-1: Screening, purification and characterization.

Bacterial species referred to as magnetotactic bacteria (MTB) biomineralize iron oxides and iron sulphides inside the cell. Bacteria can arrange themselves passively along geomagnetic field lines with the aid of these iron components known as magnetosomes. In this study, magnetosome nanoparticles, which were obtained from the taxonomically identified MTB isolate Providencia sp. PRB-1, were characterized and their antibacterial activity was evaluated. An in vitro test showed that magnetosome nanoparticles significantly inhibited the growth of Staphylococcus sp., Pseudomonas aeruginosa, and Klebsiella pneumoniae. Magnetosomes were found to contain cuboidal iron crystals with an average size of 42 nm measured by particle size analysis and scanning electron microscope analysis. The energy dispersive X-ray examination revealed that Fe and O were present in the extracted magnetosomes. The extracted magnetosome nanoparticles displayed maximum absorption at 260 nm in the UV-Vis spectrum. The distinct magnetite peak in the Fourier transform infrared (FTIR) spectroscopy spectra was observed at 574.75 cm-1. More research is needed into the intriguing prospect of biogenic magnetosome nanoparticles for antibacterial applications.

Intrinsic and extrinsic determinants of conditional localization of Mms6 to magnetosome organelles in Magnetospirillum magneticum AMB-1.

Magnetotactic bacteria are a diverse group of microbes that use magnetic particles housed within intracellular lipid-bounded magnetosome organelles to guide navigation along geomagnetic fields. The development of magnetosomes and their magnetic crystals in Magnetospirillum magneticum AMB-1 requires the coordinated action of numerous proteins. Most proteins are thought to localize to magnetosomes during the initial stages of organelle biogenesis, regardless of environmental conditions. However, the magnetite-shaping protein Mms6 is only found in magnetosomes that contain magnetic particles, suggesting that it might conditionally localize after the formation of magnetosome membranes. The mechanisms for this unusual mode of localization to magnetosomes are unclear. Here, using pulse-chase labeling, we show that Mms6 translated under non-biomineralization conditions translocates to pre-formed magnetosomes when cells are shifted to biomineralizing conditions. Genes essential for magnetite production, namely mamE, mamM, and mamO, are necessary for Mms6 localization, whereas mamN inhibits Mms6 localization. MamD localization was also investigated and found to be controlled by similar cellular factors. The membrane localization of Mms6 is dependent on a glycine-leucine repeat region, while the N-terminal domain of Mms6 is necessary for retention in the cytosol and impacts conditional localization to magnetosomes. The N-terminal domain is also sufficient to impart conditional magnetosome localization to MmsF, altering its native constitutive magnetosome localization. Our work illuminates an alternative mode of protein localization to magnetosomes in which Mms6 and MamD are excluded from magnetosomes by MamN until biomineralization initiates, whereupon they translocate into magnetosome membranes to control the development of growing magnetite crystals.IMPORTANCEMagnetotactic bacteria (MTB) are a diverse group of bacteria that form magnetic nanoparticles surrounded by membranous organelles. MTB are widespread and serve as a model for bacterial organelle formation and biomineralization. Magnetosomes require a specific cohort of proteins to enable magnetite formation, but how those proteins are localized to magnetosome membranes is unclear. Here, we investigate protein localization using pulse-chase microscopy and find a system of protein coordination dependent on biomineralization-permissible conditions. In addition, our findings highlight a protein domain that alters the localization behavior of magnetosome proteins. Utilization of this protein domain may provide a synthetic route for conditional functionalization of magnetosomes for biotechnological applications.

Nitric oxide sensor NsrR is the key direct regulator of magnetosome formation and nitrogen metabolism in Magnetospirillum.

Nitric oxide (NO) plays an essential role as signaling molecule in regulation of eukaryotic biomineralization, but its role in prokaryotic biomineralization is unknown. Magnetospirillum gryphiswaldense MSR-1, a model strain for studies of prokaryotic biomineralization, has the unique ability to form magnetosomes (magnetic organelles). We demonstrate here that magnetosome biomineralization in MSR-1 requires the presence of NsrRMg (an NO sensor) and a certain level of NO. MSR-1 synthesizes endogenous NO via nitrification-denitrification pathway to activate magnetosome formation. NsrRMg was identified as a global transcriptional regulator that acts as a direct activator of magnetosome gene cluster (MGC) and nitrification genes but as a repressor of denitrification genes. Specific levels of NO modulate DNA-binding ability of NsrRMg to various target promoters, leading to enhancing expression of MGC genes, derepressing denitrification genes, and repressing nitrification genes. These regulatory functions help maintain appropriate endogenous NO level. This study identifies for the first time the key transcriptional regulator of major MGC genes, clarifies the molecular mechanisms underlying NsrR-mediated NO signal transduction in magnetosome formation, and provides a basis for a proposed model of the role of NO in the evolutionary origin of prokaryotic biomineralization processes.

Investigation of pharmacokinetics and immunogenicity of magnetosomes.

Magnetosomes are iron oxide or iron sulphide nano-sized particles surrounded by a lipid bilayer synthesised by a group of bacteria known as magnetotactic bacteria (MTB). Magnetosomes have become a promising candidate for biomedical applications and could be potentially used as a drug-carrier. However, pharmacokinetics and immunogenicity of the magnetosomes have not been understood yet which preclude its clinical applications. Herein, we investigated the pharmacokinetics of magnetosomes including Absorption, Distribution, Metabolism, and Elimination (ADME) along with its immunogenicity in vitro and in vivo. The magnetosomes were conjugated with fluorescein isothiocyanate (Mag-FITC) and their conjugation was confirmed through fluorescence microscopy and its absorption in HeLa cell lines was evaluated using flow cytometry analysis. The results revealed a maximum cell uptake of 97% at 200 µg/mL concentration. Further, the biodistribution of Mag-FITC was investigated in vivo by a bioimaging system using BALB/c mice as a subject at different time intervals. The Mag-FITC neither induced death nor physical distress and the same was eliminated post 36 h of injection with meagre intensities left behind. The metabolism and elimination analysis were assessed to detect the iron overload which revealed that magnetosomes were entirely metabolised within 48-h interval. Furthermore, the histopathology and serum analysis reveal no histological damage with the absence of any abnormal biochemical parameters. The results support our study that magnetosomes were completely removed from the blood circulation within 48-h time interval. Moreover, the immunogenicity analysis has shown that magnetosomes do not induce any inflammation as indicated by reduced peaks of immune markers such as IL 1ß, IL 2, IL 6, IL8, IFN γ, and TNF α estimated through Indirect ELISA. The normal behaviour of animals with the absence of acute or chronic toxicities in any organs declares that magnetosomes are safe to be injected. This shows that magnetosomes are benign for biological systems enrouting towards beneficial biomedical applications. Therefore, this study will advance the understanding and application of magnetosomes for clinical purposes.