Assessing the movement of magnetotactic bacteria(MTB)under magnetic fields is a key to exploring the function of the magnetotaxis.In this study,a simple method was used to analyze the behavior of MTB,which was based on the accumulation of cells on the walls of a test tube when two permanent magnet blocks were applied on the tube.Experimental results showed a significant difference among the movements of the polar MTB,axial MTB,and ferrofluid.The polar magnetotactic cells aggregated as spots above or below the two magnet blocks besides the aggregated spots underneath the magnet blocks.By contrast,the axial magnetotactic cells aggregated only as two round spots underneath the magnet blocks,and more cells aggregated in the center than all around of the spot.For the ferrofluid,two spots were also formed underneath the magnet blocks,and the aggregated particles formed a ring shape.Magnetic calculation by finite element method was used to analyze the phenomenon,and the findings were reasonably explained by the MTB features and magnetic field theory.A scheme that differentiates polar MTB,axial MTB,and magnetic impurity could be developed,which would be beneficial to fieldworks involving MTB in the future.
Tao SongHong-Miao PanZheng WangTian XiaoLong-Fei Wu
Magnetotactic bacteria 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 magnetotactic bacteria. Here we describe 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 taxonomic group which was detected in the sampling site. Microscopy analysis revealed that QR-1 cells averaged(6.71±1.03)×(1.54±0.20) m 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 mm/s. Transmission electron microscopy based analysis showed that QR-1 cells had two tufts of fl agella at each end. Phylogenetic analysis of the 16 S r RNA genes revealed that QR-1 together with three other rod-shaped uncultivated magnetotactic bacteria are clustered into a deep branch of A lphaproteobacteria.
