Magnetosymbiosis discovery:new perspectives in magnetotaxis research

Magnetotactic bacteria have been the only known magnetoreceptive microorganisms for decades.Even if the existence of magnetotactic protists was suggested in 1986,this is only 30 years later that magnetotaxis was extended to the domain of Eukaryota,thanks to the characterization of magnetotactic symbiotic assemblies composed of a flagellated protist and bacteria biomineralizing magnetic crystals.Their mutualistic ectosymbiosis relies on a collective magnetotaxis coupled to a hydrogen-based syntrophy.This new form of cooperation challenges our view of magnetic biomineralization in prokaryotes and magnetoreception in eukaryotes.In this review,we present how magnetosymbiosis was discovered and how cooperation functions.Finally,we discuss the future research and the new perspectives such discovery brought to the field of magnetotaxis.

The discovery of magnetotactic/magnetosensitive bacteria

Magnetotactic bacteria orient and migrate along magnetic field lines in aquatic habitats. The first paper on this phenomenon was written by Richard P. Blakemore （Blakemore, 1975; 1982）.

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.

Extraction and purification of magnetic nanoparticles from strain of Leptospirillum ferriphilum

The magnetic nanoparticles were extracted from Leptospirillum ferriphilum,strain YSK,isolated from acid mine drainages by treatment with sodium dodecyl sulfate(SDS)and centrifugation through a sucrose density gradient.Transmission electron microscopy(TEM)indicates that the nanoparticles are approximately spherical with a mean diameter of 44 nm,and magnetite crystals in this size range are single magnetic domains.Energy-dispersive X-ray analysis shows that the nanoparticles primarily contain two kinds of elements,iron and oxygen.Thus it can be concluded that the magnetic particles are magnetosomes.Generally,it is thought that cellular magnetotaxis is a direct consequence of the cell possessing magnetosomes.The discovery of magnetosomes in strain YSK can provide the theoretical basis for screening efficient bioleaching bacteria which are specific to different magnetic minerals under an outer magnetic field.

Characterization of Deciliation-Regeneration Process of Tetrahymena Pyriformis for Cellular Robot Fabrication

magnetotactic Tetrahymena pyriformis GL （T. pyriformis） cells were created by the internalization of iron oxide nano particles and became controllable with a time-varying external magnetic field. Thus, T. pyriformis can be utilized as a cellular robot to conduct micro-scale tasks such as transportation and manipulation. To complete these tasks, loading inorganic or organic materials onto the cell body is essential, but functionalization of the cell membrane is obstructed by their motile organelles, cilia. Dibucaine HC1, a local anesthetic, removes the cilia from the cell body, and the functional group would be absorbed more efficiently during cilia regeneration. In this paper, we characterize the recovery of artificial magnetotactic T. pyriformis after the deciliation process to optimize a cellular robot fabrication process. After sufficient time to recover, the motility rate and the average velocity of the deciliated cells were six and ten percent lower than that of non-deciliated cells, respectively. We showed that the motile cells after recovery can still be controlled using magnetotaxis, making T. pyrfformis a good candidate to be used as a celIular robot.

Characterizing the Effect of Static Magnetic Fields on <i>C. elegans</i>Using Microfluidics

In nature, several organisms possess a magnetic compass to navigate or migrate them to desired locations. It is thought that these organisms may use biogenic magnetic matter or light-sensitive photoreceptors to sense and orient themselves in magnetic fields. To unravel the underlying principles of magnetosensitivity and magnetoreception, previous experiments have been conducted on bacteria, vertebrates, crustaceans, and insects. In this study, the model organism, C. elegans, is used to test their response and sensitivity to static magnetic fields in the range of 5 milli Tesla to 120 milli Tesla. Single wild-type C. elegans are put in microfluidic channels and exposed to permanent magnets for five cycles of thirty-second time intervals. The worm movement is recorded and analyzed with custom software to calculate the average velocity and the percentage of turning and curling. Contrary to some published studies, our results did not show a significant difference compared to control experiments. This suggests that C. elegans may not sense static magnetic fields in the range of field strengths that we tested.

Enhancement on the ammonia oxidation capacity of ammonia-oxidizing archaeon originated from wastewater:Utilizing low-density static magnetic field

Ammonia-oxidizing archaeon(AOA)could play important roles for nitrogen removal in the bioreactors under conditions such as low pH and low dissolved oxygen.Therefore,enhancing ammonia oxidation capability of AOA has great significance for water and wastewater treatment,especially under conditions like low dissolved oxygen concentration.Utilizing a novel AOA strain SAT1,which was enriched from a wastewater treatment plant by our group,the effect of magnetic field on AOA’s ammonia oxidation capability,its magnetotaxis and heredity were investigated in this study.Compared with control experiment,AOA’s maximum nitrite-N formation rate during the cultivation increased by 56.8%(0.65 mgN/(L·d))with 20 mT magnetic field.Also,it was testified that AOA possessed a certain magnetotaxis.However,results manifested that the enhancement of AOA’s ammonia oxidation capability was not heritable,that is,lost once the magnetic field was removed.Additionally,the possible mechanism of improving AOA’s ammonia oxidation capability by magnetic field was owing to the promotion of AOA single cells’growth and fission,rather than the enhancement of their ammonia oxidation rates.The results shed light on the application of AOA and methods to enhance AOA’s ammonia oxidation capability,especially in wastewater treatment processes under certain conditions.