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.

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.

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.

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.

How light affect the magnetotactic behavior and reproduction of ellipsoidal multicellular magnetoglobules?

Magnetotactic bacteria(MTB)synthesize intracellular magnetic organelles,magnetosomes,which consist of magnetic crystals that are enveloped in a membrane.Magnetosomes are organized into a chain(s)and confer on cells a magnetic dipolar moment.This magnetic property allows MTB cells to align and swim along geomagnetic field lines,a movement referred to as magnetotaxis.Some MTB species change their swim direction in response to illumination by UV,violet and blue light.Here we analyzed the polarity of morphology,magnetism,and motion in Mediterranean multicellular magnetotactic prokaryotes,also called,magnetoglobules or MMP.The magnetoglobules were assembled from 60-80 cells into an asymmetric ellipsoidal morphology with a relative narrow and large end.They swam dominantly northward,parallel to the direction of the magnetic field,with the narrow-end as the leading side.In response to a reversal in the direction of the magnetic field,they aligned quickly along the magnetic field lines and kept swimming northward.Interestingly,under constant illumination,385-nm UV light,magnetoglobules changed their swimming direction southward anti-parallel to the direction of the magnetic field,with the large-end as the leading side.The change from a northward to southward direction occurred along with an increase of swimming speed.A minimum of 35-mW/cm^(2) irradiance of UV light was sufficient to trigger the swimming re-orientation.UV radiation also triggered the unidirectional division of magnetoglobules.Together these results revealed a coordination of the polarity of magnetoglobule morphology,magnetic moment,and swimming orientation,in response to magnetic and optical stimuli.The UV triggered the reversal of magnetotaxis and magnetoglobule division indicating the ecological significance of light for multicellular magnetotactic prokaryotes.

Resazurin as an indicator of reducing capacity for analyzing the physiologic status of deep-sea bacterium Photobacterium phosphoreum ANT-2200

Resazurin(RZ)is a weakly fl uorescent blue dye and can be reduced irreversibly to highly fl uorescent pink resorufi n(RF)that is reduced reversibly to colorless dihydroresorufi n(hRF)by photodeoxygenation,chemical reaction and reductive organic compounds produced through cell metabolism.Because of the reliable and sensitive fl uorescence-color change and noninvasive features,RZ has been used widely as a redox indicator in cell viability/proliferation assays for bacteria,yeast,and mammalian cells.However,RZ is used rarely for physiological characterization of marine microorganisms.Here,we developed a custom-made irradiation and absorption-analysis device to assess the reducing capacity and physiologic status of marine bacterial cultures.We measured the absorption spectra of RZ,RF,and hRF in the presence of the reducing compound Na 2 S and under visible-light irradiation.After establishing appropriate parameters,we monitored the color changes of RZ and its reduced derivatives to evaluate the coherence between reducing capacity,bioluminescence and growth of the deep-sea bacterium Photobacterium phosphoreum strain ANT-2200 under various conditions.Emission of bioluminescence is an oxidation process dependent upon cellular reducing capacity.Growth and bioluminescence of ANT-2200 cell cultures were impeded progressively with increasing concentrations of RZ,which suggested competition for reducing molecules between RZ at high concentration with reductive metabolism.Therefore,caution should be applied upon direct addition of RZ to growth media to monitor redox reactions in cell cultures.Analyses of the instantaneous reduction velocity of RZ in ANT-2200 cell cultures showed a detrimental eff ect of high hydrostatic pressure and high coherence between the reducing capacity and bioluminescence of cultures.These data clearly demonstrate the potential of using RZ to characterize the microbial metabolism and physiology of marine bacteria.

Pleiotropic Effect of tatC Mutation on Metabolism of Pathogen Yersinia enterocolitica

Objective To analyze the impact of depletion of the twin arginine translocation （TAT） system on virulence and physiology of Yersinia enterocolitica for a better understanding of its pathogenicity. Methods We constructed a △tatC：：Sp^R mutant of Yersinia enterocolitica by P1 phage mediated transduction using Escherichia coli K-12 △tatC：：Sp^R strain as a donor. Results A Pl-mediated genetic material transfer was found between the two species of enterobacteria, indicating a great potential of acquisition of antibiotic resistance in emergency of a new threatening pathogen by genetic material exchanges. Periplasmic trimethylamine N-oxidase reductase activity was detected in the wild type E enterocolitica strain and translocation of this enzyme was completely abolished by the △tatC：：Sp^R mutation. In addition, the △tatC：：Sp^R mutation showed a pleiotropic effect on the metabolism of E enterocolitica. However, the tat mutation did not seem to affect the mobility and virulence of Y. enterocolitica under the conditions used. Conclusion Unlike other pathogenic bacteria studied, the TAT system of E enterocolitica might play an important role in the pathogenic process, which is distinct from other pathogens, such as Pseudomonas aeruginosa and enterohemorrhagic E. coli O 157：H7.

Magnetotactic bacteria and magnetoreception

A broad range of organisms have evolved abilities to exploit the Earth’s magnetic field for orientation and navigation-a behavior known as magnetoreception(Nordmann et al.,2017).Magnetotactic bacteria(MTB),diverse microbes with a patchy distribution across the bacterial tree of life,are the best known and most extensively studied magnetosensitive microorganisms.In order to efficiently achieve magnetotactic behavior,MTB biomineralize intracellular chain-arranged magnetic single-domain crystals of magnetite(Fe_(3)O_(4))and/or greigite(Fe_(3)S_(4))called magnetosomes,which are unique prokaryotic organelles that confer a magnetic moment to the cell and act as an internal compass needle(Bazylinski and Frankel,2004).

Assessing bacterial magnetotactic behavior by using permanent magnet blocks

Assessing the movement of magnetotactic bacteria(MTB)under magnetic fields is a key to exploring the function of the magnetotaxis.In this study,a simple method was used to analyze the behavior of MTB,which was based on the accumulation of cells on the walls of a test tube when two permanent magnet blocks were applied on the tube.Experimental results showed a significant difference among the movements of the polar MTB,axial MTB,and ferrofluid.The polar magnetotactic cells aggregated as spots above or below the two magnet blocks besides the aggregated spots underneath the magnet blocks.By contrast,the axial magnetotactic cells aggregated only as two round spots underneath the magnet blocks,and more cells aggregated in the center than all around of the spot.For the ferrofluid,two spots were also formed underneath the magnet blocks,and the aggregated particles formed a ring shape.Magnetic calculation by finite element method was used to analyze the phenomenon,and the findings were reasonably explained by the MTB features and magnetic field theory.A scheme that differentiates polar MTB,axial MTB,and magnetic impurity could be developed,which would be beneficial to fieldworks involving MTB in the future.

Metagenomic analysis reveals wide distribution of phototrophic bacteria in hydrothermal vents on the ultraslow-spreading Southwest Indian Ridge

Deep-sea hydrothermal vents are known as chemosynthetic ecosystems.However,high temperature vents emit light that hypothetically can drive photosynthesis in this habitat.Metagenomic studies have sporadically reported the occurrence of phototrophic populations such as cyanobacteria in hydrothermal vents.To determine how geographically and taxonomically widespread phototrophs are in deep-sea hydrothermal vents,we collected samples from three niches in a hydrothermal vent on the Southwest Indian Ridge and carried out an integrated metagenomic analysis.We determined the typical community structures of microorganisms found in active venting fields and identified populations of known potential chlorophototrophs and retinalophototrophs.Complete chlorophyll biosynthetic pathways were identified in all samples.By contrast,proteorhodopsins were only found in active beehive smoker diffusers.Taxonomic groups possessing potential phototrophy dependent on semiconductors present in hydrothermal vents were also found in these samples.This systematic comparative metagenomic study reveals the widespread distribution of phototrophic bacteria in hydrothermal vent fields.Our results support the hypothesis that the ocean is a seed bank of diverse microorganisms.Geothermal vent light may provide energy and confer a competitive advantage on phototrophs to proliferate in hydrothermal vent ecosystems.