Correlative Fluorescence And Electron Microscopic Study The Diversity And Biomineralization Of Uncultured Magnetotactic Bacteria

Magnetotactic bacteria(MTB)synthesis biofilm-coated,nano-sized,single domain magnetite or pyrite crystal particles in the cell,also known as magnetosomes.It is the only currently found prokaryotic microorganisms that exploit geomagnetic field to oriented mineralize nanocrystalline magnetite and pyrite in the cell,which is a model for studying microbial control of mineralization and microbial-mineral interactions.The results show that MTB have worldwide.distribution and rich diversities.From the morphology of the bacteria,there are cocci,vibrio,spirochetes and multicellular morphological bacterias.From the system of evolution,the magnetotactic bacterias found so far belong to five major specific groups of bacterial domain: Alphaproteobacteria,Gammaproteobacteria,Deltaproteobacteria and Nitrospira classes and the candidate phyla Latescibacteria(also known as candidate division WS3)and Omnitrophica(also known as candidate division OP3)of the Planctomycetes–Verrucomicrobia–Chlamydiae(PVC)bacterial superphylum.Transmission electron microscopy(TEM)showed that the morphologies,sizes and chain assembly patterns of different magnetotactic bacteria were different,which suggested that the biomineralization of magnetotactic bacteria could be diversified.In order to observe the specific bacteria that can interact with mineral and come from complex naturel environment under electron microscope,this paper established a method of combining fluorescence microscopy and electron microscopy to realize that the method of fluorescence microscopy observation and then corresponding electron microscope observation for more accurate study.One culture-specific strain AMB-1 and E.coli were used as experimental materials.A specific oligonucleotide probe was designed according to the magnetotactic bacteria AMB-1.A series of experimental operations and modifications were carried out on the bacterias containing E.coli and AMB-1 by fluorescence in situ hybridization.The E.coli and AMB-1 were located firstly under fluorescence microscope then the morphology of the same specific AMB-1 bacteria can be found under SEM or TEM,realising species identification(phylogenetic)and fine mineralization at the nanoscale(cell and mineral morphology,etc.)at the single cell level.Using this method,we identified one Gammaproteobacteria magnetotactic rod-shaped bacteria and one Alphaproteobacteria magnetotactic cocci-bacteria from the brackish sediments collected at the mouth of the Shihe River in Qinhuangdao,eastern China.Named SHHR-1 and SHHC-1.The morphological characteristics,crystal type and element distribution of the two kinds of bacteria were characterized by transmission electron microscopy(TEM).In order to test the ability of the coupled FISH-SEM approach to identify taxonomic groups and magnetosome types of uncultured MTB,we applied our methods to uncultured MTB cells from a more complex and diverse environment in sediments collected from Lake Miyun in north Beijing,China.Miyun MTB are phylogenetically and morphologically diverse The probe matching analysis and our combination study show that the popuLation coverage and specificity of the available popuLations were relatively limited for the magnetotactic bacteria,and more relevant fluorescence and electron microscopy were needed for the magnetotactic bacteria.Since the above method is simple and effective,it is expected to be used for biomineralization recognition research in other unicellular organisms rather than limited in magnetotactic bacteria.