Biosorption Equilibrium and Kinetics of Au（Ⅲ） and Cu（Ⅱ） on Magnetotactic Bacteria

Magnetotactic bacteria （MTB） as biosorbents for the adsorption of Au（Ⅲ） and Cu（Ⅱ） ions from aqueous solution have been investigated. The optimum adsorption conditions for both metal ions were the initial pH scope of 1-5.5 for Au（Ⅲ） and 2.0-4.5 for Cu（Ⅱ）, room temperature, biomass concentration of 10.0g.L^-1 and sorotion du-ration more than 10 min. When the initial metal concentration were within 500mg.L^-1, the maximum biosorption capacity of 1.0g of MTB （dry mass basis） for Au（Ⅲ） and Cu（Ⅱ） were calculated as 505.2mg of Au（Ⅲ） and 493.1mg of.Cu（Ⅱ） by Langmuir model in single system, respectively. The isotherm equilibrium of Au（Ⅲ） and Cu（Ⅱ） ions in the Au-Cu binary system reflected a unique phenomenon that the adsorption of Au（Ⅲ） was rein-forced and that of Cu（Ⅱ） prohibited, compared respectively-with their performances in the single metal system.When the,concentration of-Au（Ⅲ） and Cu（Ⅱ）. were below 80mg.L^-1, the waste waterafter MTB treating, wasbelow 1.0mg.L^-1, which is in conformity with Environmental Performance Standards （EPS） of Canada. Besides, all the kinetic data were fitted well to the pseudo second-order kinetic model with a high correlation coefficient （R^2〉0.999）.

Characterization of Mediterranean Magnetotactic Bacteria

Magnetotactic bacteria are a diverse group of motile prokaryotes that are ubiquitous in aquatic habitats and cosmopolitan in distribution. In this study, we collected magnetotactic bacteria from the Mediterranean Sea. A remarkable diversity of morphotypes was observed, including multicellular types that seemed to differ from those previously found in North and South America. Another interesting organism was one with magnetosomes arranged in a six-stranded bundle which occupied one third of the cell width. The magnetosome bundle was evident even under optic microscopy. These cells were connected together and swam as a linear entire unit. Magnetosomes did not always align up to form a straight linear chain. A chain composed of rectangle magnetosomes bent at a posi- tion with an oval crystal. High resolution transmission electron microscopy analysis of the crystal at the pivotal position suggested uncompleted formation of the crystal. This is the first report of Mediterranean magnetotactic bacteria, which should be useful for studies of biogeochemical cycling and geohistory of the Mediterranean Sea.

Observations on a magnetotactic bacteria-grazing ciliate in sediment from the intertidal zone of Huiquan Bay,China

Magnetotactic bacteria(MTB)are a group of prokaryotes having the ability to orient and swim along geomagnetic field lines because they contain intracellular magnetosomes that are synthesized through a biomineralization process.Magnetosomes have recently also been found in unicellular eukaryotes,which are referred to as magnetically responsive protists(MRPs).The magnetosomes have three origins in MRPs.In this study,we characterized a MTB-grazing ciliated MRP that was magnetically collected from intertidal sediment of Huiquan Bay,Qingdao,China.Based on 18S rRNA gene sequence analysis,the ciliated MRP was tentatively identified as Uronemella parafi lificum HQ.Using transmission electron microscopy,we observed that magnetosomes having 2-3 shapes were randomly distributed within this ciliate.Energydispersive X-ray spectroscopy and high-resolution transmission electron microscopy images of the magnetosomes were consistent with them being composed of magnetite.Magnetosomes having the same shape and mineral composition were also detected in MTB that occurred in the same environment as the ciliated MRP.Statistical analysis showed that the size and shape of the magnetosomes in the ciliated MRP were similar to those in MTB.The results suggest that this ciliated MRP can graze,ingest,and digest various types of MTB.It is certainly worth noting that this is the first record of MRPs in Asian aquatic sediment and suggesting they might be widely distributed.These results also support the assertion that MRPs probably contribute to the ecological cycles of iron,and expand possibilities for research into the mechanism of magnetoreception in eukaryotes.

Characterization and diversity of magnetotactic bacteria from sediments of Caroline Seamount in the Western Pacific Ocean

Magnetotactic bacteria(MTB)are a group of microorganisms capable of orientating and swimming along magnetic fields because they contain intracellular biomineralized magnetosomes composed of magnetite(Fe 3 O 4)or/and greigite(Fe_(3)S_(4)).They are ubiquitous in freshwater,brackish,and marine habitats,and are cosmopolitan in distribution.However,knowledge of their occurrence and distribution in seamount ecosystems is limited.We investigated the diversity and distribution of MTB in the Caroline Seamount(CM4).The abundance of living MTB in 12 stations in depth varying from 90 to 1545 m was 1.1×10^(3)-43.7×10^(3) inds./dm 3.Despite diverse shapes of MTB observed,magnetotactic cocci were the dominant morphotype and could be categorized into two types:1)typical cocci that appeared to have peritrichous fl agella;and 2)those characterized by having a drop-shaped form and one bundle of fl agella located at the thin/narrow end of the cell.Transmission electron microscopy(TEM)analysis revealed that the magnetosomes formed by those magnetotactic cocci are magnetite(Fe 3 O 4)with octahedral crystal habit.A total of 41 operational taxonomic units(OTUs)of putative MTB(2702 reads)were acquired from nine stations,based on high-throughput sequencing.Of these,40 OTUs belonged to the Proteobacteria phylum and one belonged to the Nitrospirae phylum.We found apparent connectivity between the MTB populations on the Caroline and Kexue(Science in Chinese)seamounts,although the diversity of MTB on Caroline was much richer than on the Kexue Seamount.Our results imply that the unique topography of seamounts and other as-yet unclear environmental factors could lead to evolution of different fl agella arrangements in magnetotactic cocci,and the occurrence of octahedral magnetite magnetosomes.

Morphological and phylogenetic diversity of magnetotactic bacteria and multicellular magnetotactic prokaryotes from a mangrove ecosystem in the Sanya River,South China

Magnetotactic bacteria(MTB)are morphologically and phylogenetically diverse prokaryotes commonly able to produce magnetic nanocrystals within intracellular membrane-bound organelles(i.e.,magnetosomes)and to swim along geomagnetic field lines.We studied the diversity of MTB in the samples collected from a mangrove area in the Sanya River,Hainan,South China,using microscopic and microbial phylogenetic methods.Results of microanalysis and observation in microscopy and energy dispersive X-ray spectroscopy(EDXS)reveal a highly morphological diversity of MTB including unicellular cocci,vibrios,rod-shaped bacteria,and three morphotypes of multicellular magnetotactic prokaryotes(MMPs).In addition,analysis of the 16S rRNA gene showed that these MTB were clustered into 16 operational taxonomic units affi liated to the Alpha-,Delta-,and Gamma-proteobacteria classes within the Proteobacteria phylum.Meanwhile,by using the coupled fluorescence and transmission electron microscopy analysis,rodshaped bacteria,vibrio,and cocci were phylogenetically and structurally identified at the single-cell level.This study demonstrated highly diverse MTB communities in the mangrove ecosystem and provide a new insight into the overall diversity of MTB.

Release the iron: does the infection of magnetotactic bacteria by phages play a role in making iron available in aquatic environments?

Magnetotactic bacteria(MTB)are ubiquitous prokaryotes that orient along magnetic field lines due to magnetosomes’biomineralization within the cell.These structures are ferrimagnetic organelles that impart a magnetic moment to the cell.To succeed in producing magnetosomes,MTB accumulate iron in(i)cytoplasm;(ⅱ)magnetosomes;and(ⅲ)nearby the organelle.It has already been estimated that a single MTB has an iron content of 10 to 100-fold higher than Escherichia coli.Phages are the most abundant entity in oceans and are known for controlling nutrient flow such as carbon and nitrogen by viral shunt and pump.The current work addresses the putative role of phages that infect MTB on the iron biogeochemical cycle.Can phage infection in MTB hosts cause a biogenic iron fertilization-like event in localized microenvironments?Are phages critical players in driving magnetosome biomineralization genes(BGs)horizontal transfer?Further investigation of those events,including frequency of occurrence,is necessary to fully comprehend MTB’s effect on iron cycling in aqueous environments.

Characterization of uncultivated magnetotactic bacteria from the sediments of Yuehu Lake, China

Marine magnetotactic bacteria were collected from the intertidal sediments of Yuehu Lake（China）, where their abundance reached 103–104 ind./cm3. Diverse morphotypes of magnetotactic bacteria were observed, including cocci and oval, vibrio-, spirillum-, rod-, elliptical-, handle- and bar-shaped forms. The magnetococci were the most abundant, and had flagella arranged in parallel within a bundle. The majority of magnetosomes were arranged in one, two or multiple chains, although irregular arrangements were also evident. All the results of high-resolution transmission electron microscopy（HRTEM） analysis show that magnetosome crystals were composed of Fe3O4, and their morphology was specific to particular cell morphotypes. By the 16 S r RNA gene sequence analysis, we found fourteen operational taxonomic units（OTUs） which were related to magnetotactic bacteria. Among these, thirteen belonged to the Alphaproteobacteria and one to the Gammaproteobacteria.Compared with known axenic and uncultured marine magnetotactic bacteria, the 16 S r RNA gene sequences of most magnetotactic bacteria collected from the Yuehu Lake exhibited sequence identities ranging from 90.1% to96.2%（〈97%）. The results indicate that microbial communities containing previously unidentified magnetotactic bacteria occur in the Yuehu Lake.

Magnetotactic bacteria from the human gut microbiome associated with orientation and navigation regions of the brain

Magnetotactic bacteria(MTB),ubiquitous in soil and fresh and saltwater sources have been identified in the microbiome of humans and many animals.MTB endogenously produce magnetic nanocrystals enabling them to orient and navigate along geomagnetic fields.Similar magnetite deposits have been found throughout the tissues of the human brain,including brain regions associated with orientation such as the cerebellum and hippocampus,the origins of which remain unknown.Speculation over the role and source of MTB in humans,as well as any association with the brain,remain unanswered.We performed a metagenomic analysis of the gut microbiome of 34 healthy females as well as grey matter volume analysis in magnetite-rich brain regions associated with orientation and navigation with the goal of identifying specific MTB that could be associated with brain structure in orientation and navigation regions.We identified seven MTB in the human gut microbiome:Magnetococcus marinus,Magnetospira sp.QH-2,Magnetospirillum magneticum,Magnetospirillum sp.ME-1,Magnetospirillum sp.XM-1,Magnetospirillum gryphiswaldense,and Desulfovibrio magneticus.Our preliminary results show significant negative associations between multiple MTB with bilateral flocculonodular lobes of the cerebellum and hippocampus(adjusted for total intracranial volume,uncorrected P<0.05).These findings indicate that MTB in the gut are associated with grey matter volume in magnetite-rich brain regions related to orientation and navigation.These preliminary findings support MTB as a potential biogenic source for brain magnetite in humans.Further studies will be necessary to validate and elucidate the relationship between these bacteria,magnetite concentrations,and brain function.

Determination of the heating efficiency of magnetotactic bacteria in alternating magnetic field

Magnetotactic bacteria(MTB)intact cells have been applied in magnetic hyperthermia therapy of tumor,showing great efficiency in heating for tumor cell inhibition.However,the detailed magnetic hyperthermia properties and optimum heat production conditions of MTB cells are still poorly understood due to lack of standard measuring equipment.The specific absorption rate(SAR)of MTB cells is often measured by home-made equipment at a limited frequency and magnetic field amplitude.In this study,we have used a commercial standard system to implement a comprehensive study of the hyperthermic response of Magnetospirillum gryphiswaldense MSR-1 strain under 7 frequencies of 144-764 kHz,and 8 field amplitudes between 10 and 45 kA/m.The measurement results prove that the SAR of MTB cells increases with magnetic field frequency and amplitude within a certain range.In combination with the magnetic measurements,it is determined that the magnetic hyperthermia mechanism of MTB mainly follows the principle of hysteresis loss,and the heat efficiency of MTB cells in alternating magnetic field are mainly aff ected by three parameters of hysteresis loop,saturation magnetisation,saturation remanent magnetisation,and coercivity.Thus when we culture MTB in LA-2 medium containing sodium nitrate as source of nitrogen,the SAR of MTB LA-2 cells with magnetosomes arranged in chains can be as high as 4925.6 W/g(in this work,all SARs are calculated with iron mass)under 764 kHz and 30 kA/m,which is 7.5 times than current commercial magnetic particles within similar size range.

Statistical approach for the culture conditions optimization of magnetotactic bacteria for magnetic cells production

The culture of Magnetospirillum magneticum WM-1 depends on several control factors that have great effect on the magnetic cells concentration. Investigation into the optimal culture conditions needs a large number of experiments So it is desirable to minimize the number of experiments and maximize the information gained from them. The orthogonal design of experiments and mathematical statistical method are considered as effective methods to optimize the culture condition of magnetotactic bacteria WMol for high magnetic cells concentration. The effects of the four factors, such as pH value of medium, oxygen concentration of gas phase in the serum bottle, C：C （mtartaric acid： m=succinic acid） ratio and NaNO3 concentration, are simultaneously investigated by only sixteen experiments through the orthogonal design L16（44） method. The optimal culture condition is obtained. At the optimal culture condition （ pH 7.0, an oxygen concentration 4.0%, C：C （mtartaric acid： m=succinic acid） ratio 1：2 and NaNO3 100 mg 1^-1）, the magnetic cells concentration is promoted tO 6.5×10^7 cells ml^-1, approximately 8.3% higher than that under the initial conditions. The pH value of medium is a very important factor for magnetic cells concentration. It can be Proved that the orthogonal design of experiment is of 90% confidence. Ferric iron uptake follows MichaelisoMenten kinetics with a Km of 2.5 pM and a Vmax of 0.83 min^-1.

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.

Electroactivity of the magnetotactic bacteria Magnetospirillum magneticum AMB-1 and Magnetospirillum gryphiswaldense MSR-1

Magnetotactic bacteria reside in sediments and stratified water columns.They are named after their ability to synthesize internal magnetic particles that allow them to align and swim along the Earth’s magnetic field lines.Here,we show that two magnetotactic species,Magnetospirillum magneticum strain AMB-1 and Magnetospirillum gryphiswaldense strain MSR-1,are electroactive.Both M.magneticum and M.gryphiswaldense were able to generate current in microbial fuel cells with maximum power densities of 27 and 11μW/m^(2),respectively.In the presence of the electron shuttle resazurin both species were able to reduce the crystalline iron oxide hematite(Fe_(2)O_(3)).In addition,M.magneticum could reduce poorly crystalline iron oxide(FeOOH).Our study adds M.magneticum and M.gryphiswaldense to the growing list of known electroactive bacteria,and implies that electroactivity might be common for bacteria within the Magnetospirillum genus.

Application of magnetotactic bacteria as engineering microrobots:Higher delivery efficiency of antitumor medicine

For a significant duration,enhancing the efficacy of cancer therapy has remained a critical concern.Magnetotactic bacteria(MTB),often likened to micro-robots,hold substantial promise as a drug delivery system.MTB,classified as anaerobic,aquatic,and gram-negative microorganisms,exhibit remarkable motility and precise control over their internal biomineralization processes.This unique ability results in the formation of magnetic nanoparticles arranged along filamentous structures in a catenary fashion,enclosed within a membrane.These bacteria possess distinctive biochemical properties that facilitate their precise positioning within complex environments.By harnessing these biochemical attributes,MTB could potentially offer substantial advantages in the realm of cancer therapy.This article reviews the drug delivery capabilities of MTB in tumor treatment and explores various applications based on their inherent properties.The objective is to provide a comprehensive understanding of MTB-driven drug delivery and stimulate innovative insights in this field.

Production,Modifi cation and Bio-Applications of Magnetic Nanoparticles Gestated by Magnetotactic Bacteria

Magnetotactic bacteria(MTB)were first discovered by Richard P.Blakemore in 1975,and this led to the discovery of a wide collection of microorganisms with similar features i.e.,the ability to internalize Fe and convert it into magnetic nanoparticles,in the form of either magnetite(Fe_(3)O_(4))or greigite(Fe_(3)S_(4)).Studies showed that these particles are highly crystalline,monodisperse,bioengineerable and have high magnetism that is comparable to those made by advanced synthetic methods,making them candidate materials for a broad range of bio-applications.In this review article,the history of the discovery of MTB and subsequent efforts to elucidate the mechanisms behind the magnetosome formation are briefly covered.The focus is on how to utilize the knowledge gained from fundamental studies to fabricate functional MTB nanoparticles(MTB-NPs)that are capable of tackling real biomedical problems.

Magnetotactic bacteria:Characteristics and environmental applications

Magnetotactic bacteria(MTB)are a group of Gram-negative prokaryotes that respond to the geomagnetic field.This unique property is attributed to the intracellular magnetosomes,which contains membrane-bound nanocrystals of magnetic iron minerals.This review summarizes the most recent advances in MTB,magnetosomes,and their potential applications especially the environmental pollutant control or remediation.The morphologic and phylogenetic diversity of MTB were first introduced,followed by a critical review of isolation and cultivation methods.Researchers have devoted to optimize the factors,such as oxygen,carbon source,nitrogen source,nutrient broth,iron source,and mineral elements for the growth of MTB.Besides the applications of MTB in modem biological and medical fields,little attention was made on the environmental applications of MTB for wastewater treatment,which has been summarized in this review.For example,applications of MTB as adsorbents have resulted in a novel magnetic separation technology for removal of heavy metals or organic pollutants in wastewater.In addition,we summarized the current advance on pathogen removal and detection of endocrine disruptor which can inspire new insights toward sustainable engineering and practices.Finally,the new perspectives and possible directions for future studies are recommended,such as isolation of MTB.genetic modification of MTB for mass production and new environmental applications.The ultimate objective of this review is to promote the applications of MTB and magnetosomes in the environmental fields.

Dynamic Model and Motion Mechanism of Magnetotactic Bacteria with Two Lateral Flagellar Bundles

Magnetotactic Bacteria （MTB） propel themselves by rotating their flagella and swim along the magnetic field lines. To analyze the motion of MTB, MTB magneto-ovoid strain MO-1 cells, each with two bundles of flagella, were taken as research object. The six-degrees-of-freedom （6-DoF） dynamic model of MO-1 was established based on the Newton-Euler dynamic equations. In particular, the interaction between the flagellum and fluid was considered by the resistive force theory. The simulated motion trajectory of MTB was found to consist of two kinds of helices： small helices restilting from the imbalance of force due to flagellar rotation, and large helices arising from the different directions of the rotation axis of the cell body and the propulsion axis of the flagellum. The motion behaviours of MTB in various magnetic fields were studied, and the simulation results agree well with the experiment results. In addition, the rotation frequency of the flagella was estimated at 1100 Hz, which is consistent with the average rotation rate for Na^＋-driven flagellar motors. The included angle of the magnetosome chain was predicted at 40° that is located within 20° to 60° range of the observed results. The results indicate the correctness of the dynamic model, which may aid research on the operation and control of MTB-propelled micro-actuators. Meanwhile, the motion behaviours of MTB may inspire the development of micro-robots with new driving mechanisms.

Biocompatibility of marine magnetotactic ovoid strain MO-1 for in vivo application

Magnetotactic bacteria are capable of biosynthesizing magnetic nanoparticles,also called magnetosomes,and swimming along magnetic field lines.The abilities endow the whole cells of magnetotactic bacteria with such applications as targeted therapy and manipulation of microrobots.We have shown that the intact marine magnetotactic bacteria MO-1 kill efficiently antibiotic-resistant pathogen Staphylococcus aureus in vivo,but the biocompatibility of this marine bacterium is unknown.In this study,the strain MO-1 was chosen to analyze its biocompatibility and potential for biomedicine applications.Results showed that MO-1 cells could be guided at 37℃ under an external magnetic field and swim in the blood plasma and urine.They could keep active locomotivity within 40 min in the plasma and urine,although their velocity slowed down.When incubated with human cells,magnetotactic bacteria MO-1 had no obvious effects on cellular viability at low dose,while the cell toxicity increased with the augmentation of the quantity of the MO-1 cells added.In the in-vivo experiments,the median lethal dose of magnetotactic bacteria MO-1 in rats was determined to be 7.9×10^(10) bacteria/kg.These results provided the foundation for the biocompatibility and safety evaluations of magnetotactic bacteria MO-1 and suggested that they could be basically used in clinical targeted therapy.

Genomic analysis of a pure culture of magnetotactic bacterium Terasakiella sp.SH-1

Magnetotactic bacteria(MTB)display magnetotaxis ability because of biomineralization of intracellular nanometer-sized,membrane-bound organelles termed magnetosomes.Despite having been discovered more than half a century,only a few representatives of MTB have been isolated and cultured in the laboratory.In this study,we report the genomic characterization of a novel marine magnetotactic spirillum strain SH-1 belonging to the genus Terasakiella that was recently isolated.A gene encoding haloalkane dehalogenase,which is involved in the degradation of chlorocyclohexane,chlorobenzene,chloroalkane,and chloroalkene,was identified.SH-1 genome contained cysCHI and soxBAZYX genes,thus potentially capable of assimilatory sulfate reduction to H_(2)S and using thiosulfate as electron donors and oxidizing it to sulfate.Genome of SH-1 also contained genes encoding periplasmic dissimilatory nitrate reductases(napAB),assimilatory nitrate reductase(nasA)and assimilatory nitrite reductases(nasB),suggesting that it is capable of gaining energy by converting nitrate to ammonia.The pure culture of Terasakiella sp.SH-1 together with its genomic results off ers new opportunities to examine biology,physiology,and biomineralization mechanisms of MTB.

Redox control of magnetosome biomineralization

Magnetotactic bacteria can orientate in the Earth’s magnetic field to search for their preferred microoxic environments,which is achieved by their unique organelles,the magnetosomes.Magnetosomes contain nanometer-sized crystal particles of magnetic iron minerals,which are only synthesized in lowoxygen environments.Although the mechanism of aerobic repression for magnetosome biomineralization has not yet fully understood,a series of studies have verified that redox modulation is pivotal for magnetosome formation.In this review,these advances in redox modulation for magnetosome biosynthesis are highlighted,mainly including respiration pathway enzymes,specific magnetosome-associated redox proteins,and oxygen-or nitrate-sensing regulators.Furthermore,their relationship during magnetosome biomineralization is discussed to give insight into redox control and biomineralization and inspire potential solutions for the application of respiration pathways to improve the yields of magnetosome.

Recover vigorous cells of Magnetospirillum magneticum AMB-1 by capillary magnetic separation

Cultivable magnetotactic bacteria(MTB) in laboratory can provide sufficient samples for molecular microbiological and magnetic studies.However,a cold-stored MTB strain,such as Magnetospirillum magneticum AMB-1,often loses its ability to synthesize magnetosomes and consequently fails to sense the external magnetic field.It is therefore important to quickly recover vigorous bacteria cells that highly capable of magnetosome producing.In this study,a modified capillary magnetic separation system was designed to recover a deteriorating strain of Magnetospirillum magneticum AMB-1 that long-term cold-stored in a refrigerator.The results show that all cells obtained after a 3-cycle treatment were vigorous and had the ability to produce magnetosomes.Moreover,the 3rd-cycle recovered cells were able to form more magnetosome crystals.Compared with the colony formation method,this new method is time-saving,easily operated,and more efficient for recovering vigorous MTB cells.