Study On Diversity Of Magnetogenic Bacteria In Daqing Urban Area

Magnetotactic bacteria(MTB)are microorganisms that have magnetotactic ability to move along the direction of the earth's magnetic lines.The nanoscale(35-120 nm)magnetosomes are synthesized by intracellular mineralization and its component is magnetite(Fe3O4)or pyrrhotite(Fe3S4).The research on the MTB diversity was carried out later in our country.Previous studies found that the MTB were distributed in lakes and oceans in southern and northern China,but the distribution of MTB in extreme environments was rarely reported.The wide distribution of slight saline-alkaline lakes in Daqing is an ideal environment for studying the physiological ecology and population distribution of the MTB.Therefore,this study selected 9 representative wetland lakes in Daqing area,and analyzed the diversity of the MTB in Daqing area.Moreover,the environmental factors of their habitat were also analyzed.Combined 16 S rRNA gene sequence,the diversity of the MTB was analysised in two aspects of morphological diversity and phylogenetic diversity using optical microscope and transmission electron microscopy(TEM).Besides,the major environmental factors in their habitat were futher examined.Firstly,the MTB in the environmental samples were observed by optical microscope.After,the amount of bacteria was suitable,magnetic separation and purification of the the MTB were conducted to prepare TEM samples using capillary tube.After purification,the 16 S rRNA gene sequences were amplified by PCR and clone libraries were constructed for sequencing.The data was analyzed to construct phylogenetic trees.Finally the phylogenetic classification of the obtained sequences was determined.The differences in pH,total nitrogen,total carbon and salinity at every sampling point were analysised.Canoco 5.0 software was used to perform RDA analysis on the environmental factors at each sampling point,and the relationship between environmental factors and the distribution of the MTB was inferred.At last,the representative bacteria were identified by combining fluorescence microscopy and electron microscopy.Optical microscope observation results showed that the single-cell morphologies of the MTBin the sample were spherical,curved,and spiral.Observed under electron microscope,shapes of the magnetosomes mainly were prismatic and octahedral,and its components are all iron oxides.The magnetosome chains have single-stranded,double-stranded,four-stranded and irregularly distributed chains.Environmental factor analysis showed that there were significant differences in total carbon,salinity,nitrogen content in the soil and water respectively,p H among the nine wetlands and lakes.From the principal component analysis of environmental factors,we can conclued that Dongjiapao,Chengfenghu and Minghu have similar environments;Hongqipao Reservoir and Binzhou Lake have similar environments;Heiyu Lake and other lakes have certain differences in environmental similarities.The sequence analysis results showed that the phylogenetic classification belongs to the Alphaproteobacteria class;the Magnetospirillum and the Magnetococcus are dominant;the similarity of sequence is less than 98% and 93%,respectively,which proves that the the MTB in our study exist new species and new genus.The results of RDA analysis showed that both the Magnetococcus and the Magnetospirillum were positively correlated with total carbon,nitrogen content in the soil,salinity and negatively correlated with pH and nitrogen content in the water.Meanwhile,total carbon and soil total nitrogen have the greatest impact on the MTB.Through the method of combining fluorescence microscopy and electron microscopy,the sequence of a new strain LFSD-4 has 92% similarity with the database of Longfeng wetland was successfully identified.The morphological characteristics of the corresponding strains were obtained.The morphology of the MTB and the number,size,shape,as well as arrangement of magnetosome was diverse in the slight saline-alkaline lakes at Daqing area.The the MTB with two main dominant forms were found in the Daqing area,and in saline-alkaline lakes,the magnetospirillum was dominant in the number,which was a new discovery.Most of the the MTB in the Daqing area belonged to Alphaproteobacteria class.It was speculated that the the MTB in the saline-alkaline lake area were dominated by Alphaproteobacteria class.There was difference in the diversity of the MTB in 9 wetland lakes.So,it was speculated that the cause of this difference was the environmental factors or the type of water body.RDA data analysis showed that environmental factors had an important influence on the distribution of the MTB.In this study,the method of combining fluorescence microscopy and electron microscopy was used to achieve accurate observation of the MTB in the single-cell level,and to promote the understanding of the MTB resources and microbial mineralization,then provide a basis for the relationship between the types of the MTB and environmental factors in the future.