SOUTH-SEEKING MAGNETOTACTIC BACTERIA IN THE SOUTHERN-HEMISPHERE
SOUTH-SEEKING MAGNETOTACTIC BACTERIA IN THE SOUTHERN-HEMISPHERE
复制标题
DOI：
10.1038/286384a0
复制
发表时间：
1980-01-01
期刊：
影响因子：
64.8
通讯作者：
KALMIJN, AJ
中科院分区：
文献类型：
--
作者：
BLAKEMORE, RP;FRANKEL, RB;KALMIJN, AJ
在北方半球的海洋和淡水沉积物中观察到几种水生细菌，它们在地球磁场中定向，并沿沿着磁场线以优选方向（趋磁性）游泳1，2。它们的取向是由于一个或多个单域磁铁矿颗粒的胞质内链3。这些线性排列的颗粒赋予细菌一个净磁偶极矩，平行于运动轴。北方半球的趋磁细菌与单向运动游泳一致的方向磁场，即地磁北1，2，4。这意味着它们的磁偶极子是系统地定向的，寻北磁极向前。磁极性可以通过高场强（1-2 µs，300-600 G）的单个磁脉冲逆转，然后这些细菌沿着磁场线向南游动5。由于地球磁场的倾斜，在北方半球向北游动的趋磁细菌以随纬度增加的角度向下定向。有人认为，这种向下的运动通过引导细菌在被驱逐时返回沉积物而赋予生物优势1。根据这一假设，南半球的趋磁细菌将有望向南游到底部。我们在这里报告几种形态类型的趋磁细菌存在于南半球的沉积物。这些细菌确实一直向南游，因此如假设的那样，沿着地球倾斜的磁场线沿着。正如电子显微镜所揭示的那样，它们含有类似于在北方半球的趋磁细菌中观察到的电子不透明颗粒的内部链。像它们的北方对应物一样，它们的磁极性可以永久逆转，并且不能被消磁。我们还报告了北方半球的趋磁细菌在南半球的磁场条件下培养，确认向下定向运动的生物相关性。
Several species of aquatic bacteria which orient in the Earth's magnetic field and swim along magnetic field lines in a preferred direction (magnetotaxis) have been observed in marine and freshwater sediments of the Northern Hemisphere1,2. Their orientation is due to one or more intracytoplasmic chains of single-domain magnetite particles3. These linearly arranged particles impart a net magnetic dipole moment to the bacterium, parallel to the axis of motility. Northern Hemisphere magnetotactic bacteria with unidirectional motility swim consistently in the direction of the magnetic field, that is, to the geomagnetic North1,2,4. This implies that their magnetic dipole is systematically orientated with the North-seeking pole forward. The magnetic polarity can be reversed by single, magnetic pulses of high field strength (1–2 µs, 300–600 G), and these bacteria then swim along magnetic field lines to the South5. Due to the inclination of the Earth's magnetic field, magnetotactic bacteria which swim to the North in the Northern Hemisphere are directed downward at an angle increasing with latitude. It has been suggested that this downward-directed motion confers a biological advantage by guiding the bacteria, when dislodged, back to the sediments1. On the basis of this hypothesis, magnetotactic bacteria of the Southern Hemisphere would be expected to swim to the South to reach the bottom. We report here several morphological types of magnetotactic bacteria present in sediments of the Southern Hemisphere. These bacteria indeed swim consistently to the South, hence downward along the Earth's inclined magnetic field lines, as hypothesized. As revealed by electron microscopy, they contain internal chains of electron-opaque particles similar to those observed in magnetotactic bacteria from the Northern Hemisphere. Like their Northern Hemisphere counterparts, their magnetic polarity can be permanently reversed and they cannot be demagnetized. We also report on Northern Hemisphere magnetotactic bacteria incubated in Southern Hemisphere magnetic conditions, confirming the biological relevance of downward directed motility.