Effect Of Static Magnetic Field On Magnetotactic Bacteria Community In Freshwater Sediment Samples From Different Sources

Magnetic field,a physical phenomenon,ubiquitous in the Universe.It is very well known that the earth's magnetic field paly a substantial role in the origin and development of life.Magnetotactic bacteria(MTB),one of the ancient microorganisms on the earth,can absorb iron and/or sulfur elements in the external environment to form magnetic nanoparticles(Fe3O4 or Fe3S4)in the body.They distribute widely in fresh water,salt water and humid soil environments.MTB are an ideal organism to study the adaptation mechanism of microbes to magnetic field because of the presence of magnetic materials in the body,which enables MTB to move in a direction along the earth's magnetic field and the applied magnetic field.At present,the studies on the effect of magnetic field on MTB focus on single strain,and there is a lack of systematic investigation on the influence of MTB community.Here,we select MTB in freshwater sediments from three different sources(Chagan lake,Zhalong wetland,and the Yangtze river)as the research objects.The freshwater sediments were incubated under the applied static magnetic field strength(geomagnetic field 0.5 Gs,50 Gs and 100 Gs)and the exposure times in 50 Gs(1 weeks,5 weeks,8 weeks,and 11 weeks),respectively.The MTB samples were obtained using magnetic purification technology.The Hiseq2500 high-throughput sequencing technology,q PCR technology and PICRUSt were used to analyze the phylogenetic diversity of MTB,to investigate the change in the absolute abundance of MTB community,and to reveal the effect of magnetic field on the function of MTB community.Results indicated that the diversity of freshwater MTB showed a single-peak trend and reached a peak at 50 Gs with increasing magnetic field.The change in magnetic field strength showed no significant effect on the main MTB groups in Chagan lake samples,while the main genera of MTB in Zhalong wetland and Yangtze river samples significantly changed under the magnetic field strength of 100 Gs.Planctomycetes,Proteobacteria and Actinobacteria were the main phyla of MTB in Chagan lake samples under different magnetic field intensity,and the main genera were hgc I_clade and Gemmataceae.The main MTB in Zhalong Wetland and Yangtze river samples were Platescibacteria and Proteobacteria.The dominant genera were Pseudomonas and Candidatus Moranbacteria in Zhalong wetland and Yangtze river sample,respectively,under low intensity of magnetic field(0.5 Gs and 50 Gs),However,the dominant genera changed to Acinetobacter and hgc I_clade,respectively under 100 Gs magnetic field.The MTB diversity of Chagan lake and Yangtze river samples under different exposure time in a 50 Gs magnetic field reached the highest in the 5th week,and appeared in the 8th week for the Zhalong wetland samples.The freshwater MTB was exposed to 50 Gs for 1 week,and its dominant MTB genus differed significantly from 0.5 Gs.The Chagan lake samples changed from hgc I_clade to Gemmataceae,while the relative abundance of Acinetobacter in Zhalong wetland and Yangtze river samples increased significantly.Additionally,increasing the magnetic field can promote the synergy between the dominant bacteria and Herbaspirillum magnetovibio.The results also showed that the peak of the absolute abundance of freshwater MTB appeared at 50 Gs with the increase of the magnetic field intensity.The MTB absolute abundance range were 3.02×102 to 3.46×102 copies/g for the Chagan lake samples,3.91×102 to 4.87×102 copies/g for the Zhalong wetland samples,and 2.29×102 to 3.20×102 copies/g for the Yangtze River samples.The relative abundances of freshwater MTB from the three sources increase first and then decrease with the increase of the duration of the exposure of 50 Gs magnetic field.The absolute abundances of MTB in all samples under 50 Gs were significantly higher than those under the 0.5 Gs magnetic field.In addition,the analysis of the correlation between the exposure time and the absolute abundance of fresh water MTB shows that the magnetic field treatment can promote the growth peak of MTB ahead of time.Additionally,the analysis of the function of freshwater MTB community under different magnetic field intensities showed that the higher relative abundance of Carbohydrate metabolism,Amino acid metabolism and Global and overview maps appeared in all samples and showed less effected by magnetic field strength.It can be found that 22 metabolic pathways of the MTB community in Chagan lake samples changed significantly with increasing magnetic field.There are 42 significant metabolic pathways in Zhalong wetland samples,while only 5 in Yangtze river samples(P <0.05).The relative abundance of Membrane transport and Energy metabolism functions were highest for all samples under 50 Gs static magnetic field.It also can be observed that the 50 Gs magnetic field can promote Bacterial chemotaxis in Zhalong wetland.The exposure times have a strong effect on the Two-component system and Carbon metabolism of Chagan lake samples and the Yangtze river MTB flora,respectively,while it can weaken the Membrane transport and Nucleotide metabolism of MTB community in the Zhalong wetland samples.From the perspective of the metabolic function of C,N,S,and Fe,the relative abundance of Carbon metabolism of freshwater MTB community in all samples were increased by the exposure under 50 Gs magnetic field,and showed significant changes with increasing exposure time(P <0.05).Nitrogen metabolism and Sulfur metabolism showed significant changes and their abundances in Chagan lake and Yangtze river samples increased,respectively.The functions related to Fe metabolism of MTB community in Chagan lake and Yangtze river samples also changed significantly with increasing exposure time(P <0.05).In summary,the variation of magnetic field intensity has a greater impact on the diversity of freshwater MTB than the exposure time.The absolute abundance of freshwater MTB community from different sources reached the highest when increasing the static magnetic field of 50 Gs,while the absolute abundance decreased significantly when the magnetic field strength was 100 Gs.The time of magnetic exposure has a greater effect on the function of freshwater MTB community,and the increase of the magnetic field has a greater contribution to the iron cycle of the Yangtze River sample sediments.This study provides basic materials for further research on the mechanism of the influence of magnetic fields on microorganisms.