| Magnetotactic bacteria(MTB)are a group of Gram-negative bacteria that synthesize magnetic crystals,enabling them to navigate in relation to magnetic field lines.Morphologies of magnetotactic bacteria include spirillum,coccoid,rod,vibrio,and multicellular morphotypes.The coccid shape is generally the most abundant morphotype among MTB magnetotactic bacteria.Here we described a species of giant rod-shaped magnetotactic bacteria(designated QR-1)collected from sediment in the low tide zone of Huiquan Bay(Yellow Sea,China).This morphotype accounted for 90% of the magnetotactic bacteria collected,and the only one taxonomic group which was detected in the sampling site.Microscopy analysis revealed that QR-1 cells averaged 6.71 ± 1.03 ?m × 1.54 ± 0.20 ?m in size,and contained in each cell 42~146 magnetosomes that are arranged in a bundle formed one to four chains along the long axis of the cell.The QR-1 cells displayed axial magnetotaxis with an average velocity of 70 ± 28 ?m/s.Transmission electron microscopy based analysis showed that QR-1 cells had two tufts of flagella at each end.Phylogenetic analysis of the 16 S rRNA genes revealed that QR-1 together with three other rod-shaped uncultivated magnetotactic bacteria is clustered into a deep branch of Alphaproteobacteria.We found three rod-shaped MTB strains shared similar morphological characteristics with QR-1 in intertidal sediments from Lake Yuehu,Rongcheng and Marseille.They were divided into two parts,had several refractive vesicles at the middle of the cell and large inclusion particles at their poles,and were able to exhibit axial magnetotactic movement.These three strains were unusually large in size;both FM-t and FM-w were longer than 10 ?m.FM-t cells had elongated prismatic magnetosome crystals and two parallel magnetsome chains arranging along the long axial of cells.In this study we used microsorting combined with single cell whole genome amplification to identify the 16 S rRNA gene of QR-1 and analyze its taxonomic affiliation.The analysis results showed that the three rod-shaped MTB were three new species belonging to three new genera and affiliate with the Alphaproteobacteria.Among all the secondary marine ecosystems,the MTB diversity in sediments of coral reef ecosystems was rarely reported.In this study,we applied ecological investigation to reveal the diversity and characteristics of MTB in sediments from Paracel Islands coral reef habitat.The results showed that the Paracel Islands coral reef habitats had a very high MTB diversity.MTB morphologies included spirillum,coccoid,rod,vibrio,and multicellular morphotypes,and morphologies of magnetosomes included bullet-shaped magnetosomes which were approximately 90% of total magnetosomes,prismatic magnetosomes,and irregular-shaped magnetosomes.Some MTB cells contained both bullet-shaped and irregular-shaped magnetosomes.Phylogenetic analysis revealed that 9 MTB species belonging to Alphaproteobacteria,Deltaproteobacteria and Nitrospirae were identified from coral reef sediments in Paracel Islands,including 4 new species belonging to the 2 new genera.Magnetospira sp.QH-2 is a marine magnetotactic spirillum,isolated from the intertidal zone of Yellow Sea,China.It was predicted that the trait that its magnetosomes in a chain display a relatively large size distribution is related to the function of mamK-encoded protein,namely Mam K.We found that mamK gene codes for 1086 bp,and MamK which belonged to the NBD_sugar-kinase_HSP70_actin superfamily was composed of 361 amino acids and did not contain any trans-membrane domain.Based on the differences of the phylogenetic trees,we determined that the acquisition of magnetosome island and bacteria evolution were possibly two independent processes.Whereas the morphology feature of magnetotactic spirillum both in fresh water and marine were similar,their phylogenetic statuses were different to some extent,and that may indicated the adaptive evolutions of this magnetotactic spirillum. |
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