Experimental observation of magnetosome chain collapse in magnetotactic bacteria: Sedimentological, paleomagnetic, and evolutionary implications
Experimental observation of magnetosome chain collapse in magnetotactic bacteria: Sedimentological, paleomagnetic, and evolutionary implications
复制标题
DOI：
10.1016/j.epsl.2006.03.041
复制
发表时间：
2006-05-30
影响因子：
5.3
通讯作者：
Taguchi, Takahisa
中科院分区：
文献类型：
--
作者：
Kobayashi, Atsuko;Kirschvink, Joseph L.;Taguchi, Takahisa
趋磁细菌沉淀单畴磁铁矿（Fe 3 O 4）和/或硫铁矿（Fe 3S 4）的胞内晶体，其通常与淡水和海洋沉积物的天然还原磁化（NRM）有关。在体内，磁性晶体通常排列成链，使得它们的力矩加在一起，产生足够高的净细胞力矩，使细胞被动地旋转以与地磁场对齐。静磁/生物物理分析表明，这种安排是动态平衡，将自发崩溃没有支持机制。过去对浅海碳酸盐岩的岩石磁性分析表明，在成岩和石化过程中确实发生了部分塌陷，为了校正这种效应，我们通过连续超声和洗涤剂处理诱导了Magnetotacellum magnetotacticum菌株MS-1的磁小体链塌陷，并通过岩石磁性分析和TEM监测了这种变化。虽然已经推测细胞壁和相关的膜结构起到防止磁小体链崩溃的作用，但我们的数据表明，磁小体线性在细胞被破坏后很长时间内仍然存在。这是一致的，在一些magnetotcocci磁小体链通过细胞内部，排除连续接触细胞壁，并暗示额外的支持结构存在于某些species.Using TEM断层重建与磁技术，防止链崩溃准备，我们研究了三维超微结构的磁小体没有死后磁小体运动的问题。这种方法揭示了细胞内的有机鞘的存在下，肌动蛋白样丝最近报道的磁小体，我们假设进化到保持晶体在适当的位置，并提高他们的能力，以保持沉积物中的NRM链。由于两种趋磁细菌的基因组含有几种已知真核细胞骨架蛋白的明显同源物，趋磁性的自然选择可能在真核细胞骨架前体的进化中发挥了作用。这个鞘的存在也与ALH 84001中与推定的磁化石链相关的电子半透明材料的观察一致。(c)2006 Elsevier B. V.保留所有权利。
Magnetotactic bacteria precipitate intracellular crystals of single-domain magnetite (Fe3O4) and/or greigite (Fe3S4), which have often been implicated in carrying the natural remanent magnetization (NRM) of freshwater and marine sediments. In vivo, the magnetic crystals are usually aligned in chains such that their moments add together, generating net cellular moments high enough to rotate the cells passively to align with the geomagnetic field. A magnetostatic/biophysical analysis demonstrates that this arrangement is out of dynamic equilibrium and would collapse spontaneously without a support mechanism. Past rock magnetic analyses of shallow water marine carbonates suggest that partial collapse does occur during diagenesis and dolomitization.To calibrate this effect we induced magnetosome chain collapse in Magnetospirillum magnetotacticum strain MS-I by progressive sonification and treatment with detergents and monitored the changes with rock magnetic analysis and TEM. Although it has been speculated that the cell wall and associated membrane structures act to prevent magnetosome chain collapse, our data indicate that magnetosome linearity persists long after cells are disrupted. This is consistent with prior observations that in some magnetotcocci the magnetosome chains pass through the cell interior, precluding continuous contact with the cell wall and implying additional support structures exist in some species.Using TEM tomographic reconstructions prepared with a magnetic technique that prevents chain collapse, we examined the three dimensional ultrastructure of magnetosomes without the problem of post-mortem magnetosome motion. This method revealed the presence of an intracellular organic sheath beyond that of actin-like filaments reported recently that follows the chain of magnetosomes, which we postulate evolved to hold the crystals in place and enhances their ability to preserve NRM in sediments. As the genomes of two magnetotactic bacteria contain several apparent homologues of known eukaryotic cytoskeletal proteins, natural selection for magnetotaxis may have played a role in the evolution of precursors to the eukaryotic cytoskeleton. The presence of this sheath is also consistent with the observation of electron translucent material associated with putative magnetofossil chains in ALH84001. (c) 2006 Elsevier B.V. All rights reserved.