中文摘要：

光学显微镜下直观显示水体环境中趋磁细菌滑磁场方向定向排列和游动，人们对其认识主要来自这些镜下观察的总结。但实际上趋磁细菌主要生活在沉积物环境中，很难对它们进行直接规察。因此，趋磁细菌在沉积物环境中的趋磁性、趋化性、以及在记录古地磁过程中可能起到的作用等方面均尚未得到足够实际观测数据的支持。本研究利用脉冲磁场反转趋磁细菌（Candidatus Magnetobacterium bavaricum ）极性的特性，将趋北趋磁细菌（NS）转变为趋南趋磁细菌（SS），并在只含有Ns的沉积物中以脉冲磁场反转的SS为“示踪体”，分析趋磁细菌在沉积物环境中的趋磁性和趋化性。使沉积物所处的外界磁场与脉冲磁场方向保持一系列角度Ф（0°～180°），利用施加脉冲磁场后出现的SS％与Ф关系估算趋磁细菌在沉积物中沿外界磁场的排列程度，证实了趋磁细菌在沉积物中沿地磁场排列程度非常低（〈1％）。将脉冲SS分别置于4种不同的磁场条件（磁场方向指向上、指向下和水平）和生存环境（上部适宜环境和下部不宜环境），一定时间ss的垂直分布权相对直观地证实了：趋磁细菌游动方向受趋化性决定，趋磁性的优势在于使趋磁细菌更有效地到达其最最佳生存环境。脉冲磁场方法在理解和研究沉积物中趋磁细菌趋磁性、趋化性和古地磁应用方面有可观的应用用前景。

英文摘要：

Magnetotactic bacteria （MTB） in water drop assays can be conveniently observed under optical microscope, i.e. MTB are aligned by magnetic field and migrate along field lines. The current knowledge about MTB and magnetotaxis are basically attributed to the observations in water under optical microscope. However, MTB mainly live in sediment, which differs a lot from water environment in physical and chemical conditions. Lacking knowledge of MTB in sediment hinders one＇s profound understanding of magnetotactic advantages, chemotaxis and paleomagnetic implication. The challenge of studying MTB in sediment is that MTB are impossible to be directly observed. Herein we proposed the application of pulsed magnetic field in studying MTB magnetotaxis and chemotaxis in sediment environments. MTB, more specifically rod-shaped Candidatus Magnetobacterium bavaricum （MB） collected from lake Chimsee in south of Germany, are north-seeking （NS） cells by swimming parallel to external magnetic field B （0.86mT）. The NS ceils aligned with B were imposed by a strong （maximum 110mT） and short （50ms） pulsed magnetic field P in opposite direction to B. Consequently NS were converted to SS （termed pulsed SS） , swimming in opposite direction with NS. These pulsed SS cells were treated as tracers in initially SS-exclusive sediment for the purpose to investigate magnetotaxis （i. e. MB alignment） and chemotaxis （i.e. MB migration） in sediment. In the first experiment, water drop assays and sediment cube with NS MB were respectively imposed by P at the angle Ф （0°- 180°） with B. After each pulse, SS% defined as 100% xSS/（NS＋SS） was obtained by respectively counting NS and SS numbers in two sides of the water drop assay. The variations of SS% versus Ф were modeled with Von-Mises Fisher distribution, which gave a best-fit alignment degree 3.2% for MB in sediment. Provided MB obeyed Langevin law, MB alignment in present geomagnetic field （e.g. 50μT） was expected as low as 〈1%, much lower t