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
Cryptochromes （CRYs） are blue and UV light photoreceptors, known to play key roles in circadian rhythms and in the light-dependent magnetosensitivity of insects. Two novel cryptochrome genes were cloned from the brown planthopper, and were given the designations of Nlcryl and Nlcry2, with the accession numbers KM108578 and KM108579 in GenBank. The complementary DNA sequences ofNlcryl andNlcry2 are 1935 bp and 2463 bp in length, and they contain an open reading frame of 1629 bp and 1872 bp, encoding amino acids of 542 and 623, with a predicted molecular weight of 62.53 kDa and 70.60 kDa, respectively. Well-conserved motifs such as DNA-photolyase and FAD-binding-7 domains were observed in Nlcry1 and Nlcry2. Phylogenetic analysis demonstrated the proteins of Nlcry1 and Nlcry2 to be clustered into the insect＇s cryptochrome 1 and cryptochrome 2, respectively. Quantitative polymerase chain reaction showed that the daily oscillations of messenger RNA （mRNA） expression in the head of the brown planthopper were mild for Nlcryl, and modest for Nlcry2. Throughout all developmental stages, Nlcryl and Nlcry2 exhibited extreme fluctuations and distinctive expression profiles. Cryptochrome mRNA expression peaked immediately after adult emergence and then decreased subsequently. The tissue expression profiles of newly emerged brown planthopper adults showed higher expression levels of CRYs in the head than in the thorax or abdomen, as well as significantly higher levels of CRYs in the heads of the macropterous strain than in the heads of the brachypterous strain. Taken together, the results of our study suggest that the two cryptochrome genes characterized in the brown planthopper might be associated with developmental physiology and migration.
Jing-Jing XuGui-Jun WanDing-Bang HuJuan HeFa-Jun ChenXian-Hui WangHong-Xia HuaWei-Dong Pan
